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diff --git a/Scenario_Seperate_Sections/Section_1_2_VNF UseCases.rst b/Scenario_Seperate_Sections/Section_1_2_VNF UseCases.rst new file mode 100644 index 0000000..57dfbc0 --- /dev/null +++ b/Scenario_Seperate_Sections/Section_1_2_VNF UseCases.rst @@ -0,0 +1,731 @@ +============ +HA Use Cases +============ + +************** +1 Introduction +************** + +This use case document outlines the model and failure modes for NFV systems. Its goal is along +with the requirements documents and gap analysis help set context for engagement with various +upstream projects. The OPNFV HA project team continuously evolving these documents, and in +particular this use case document starting with a set of basic use cases. + +***************** +2 Basic Use Cases +***************** + + +In this section we review some of the basic use cases related to service high availability, +that is, the availability of the service or function provided by a VNF. The goal is to +understand the different scenarios that need to be considered and the specific requirements +to provide service high availability. More complex use cases will be discussed in +other sections. + +With respect to service high availability we need to consider whether a VNF implementation is +statefull or stateless and if it includes or not an HA manager which handles redundancy. +For statefull VNFs we can also distinguish the cases when the state is maintained inside +of the VNF or it is stored in an external shared storage making the VNF itself virtually +stateless. + +Managing availability usually implies a fault detection mechanism, which triggers the +actions necessary for fault isolation followed by the recovery from the fault. +This recovery includes two parts: + +* the recovery of the service and +* the repair of the failed entity. + +Very often the recovery of the service and the repair actions are perceived to be the same, for +example, restarting a failed application repairs the application, which then provides the service again. +Such a restart may take significant time causing service outage, for which redundancy is the solution. +In cases when the service is protected by redundancy of the providing entities (e.g. application +processes), the service is "failed over" to the standby or a spare entity, which replaces the +failed entity while it is being repaired. E.g. when an application process providing the service fails, +the standby application process takes over providing the service, while the failed one is restarted. +Such a failover often allows for faster recovery of the service. + +We also need to distinguish between the failed and the faulty entities as a fault may or +may not manifest in the entity containing the fault. Faults may propagate, i.e. cause other entities +to fail or misbehave, i.e. an error, which in turn might be detected by a different failure or +error detector entity each of which has its own scope. Similarly, the managers acting on these +detected errors may have a limited scope. E.g. an HA manager contained in a VNF can only repair +entities within the VNF. It cannot repair a failed VM, in fact due to the layered architecture +in the VNF it cannot even know whether the VM failed, its hosting hypervisor, or the physical host. +But its error detection mechanism will detect the result of such failures - a failure in the VNF - +and the service can be recovered at the VNF level. +On the other hand, the failure should be detected in the NFVI and the VIM should repair the failed +entity (e.g. the VM). Accordingly a failure may be detected by different managers in different layers +of the system, each of which may react to the event. This may cause interference. +Thus, to resolve the problem in a consistent manner and completely recover from +a failure the managers may need to collaborate and coordinate their actions. + +Considering all these issues the following basic use cases can be identified (see table 1.). +These use cases assume that the failure is detected in the faulty entity (VNF component +or the VM). + + +*Table 1: VNF high availability use cases* + ++---------+-------------------+----------------+-------------------+----------+ +| | VNF Statefullness | VNF Redundancy | Failure detection | Use Case | ++=========+===================+================+===================+==========+ +| VNF | yes | yes | VNF level only | UC1 | +| | | +-------------------+----------+ +| | | | VNF & NFVI levels | UC2 | +| | +----------------+-------------------+----------+ +| | | no | VNF level only | UC3 | +| | | +-------------------+----------+ +| | | | VNF & NFVI levels | UC4 | +| +-------------------+----------------+-------------------+----------+ +| | no | yes | VNF level only | UC5 | +| | | +-------------------+----------+ +| | | | VNF & NFVI levels | UC6 | +| | +----------------+-------------------+----------+ +| | | no | VNF level only | UC7 | +| | | +-------------------+----------+ +| | | | VNF & NFVI levels | UC8 | ++---------+-------------------+----------------+-------------------+----------+ + +As discussed, there is no guarantee that a fault manifests within the faulty entity. For +example, a memory leak in one process may impact or even crash any other process running in +the same execution environment. Accordingly, the repair of a failing entity (i.e. the crashed process) +may not resolve the problem and soon the same or another process may fail within this execution +environment indicating that the fault has remained in the system. +Thus, there is a need for extrapolating the failure to a wider scope and perform the +recovery at that level to get rid of the problem (at least temporarily till a patch is available +for our leaking process). +This requires the correlation of repeated failures in a wider scope and the escalation of the +recovery action to this wider scope. In the layered architecture this means that the manager detecting the +failure may not be the one in charge of the scope at which it can be resolved, so the escalation needs to +be forwarded to the manager in charge of that scope, which brings us to an additional use case UC9. + +We need to consider for each of these use cases the events detected, their impact on other entities, +and the actions triggered to recover the service provided by the VNF, and to repair the +faulty entity. + +We are going to describe each of the listed use cases from this perspective to better +understand how the problem of service high availability can be tackled the best. + +Before getting into the details it is worth mentioning the example end-to-end service recovery +times provided in the ETSI NFV REL document [REL]_ (see table 2.). These values may change over time +including lowering these thresholds. + +*Table 2: Service availability levels (SAL)* + ++----+---------------+----------------------+------------------------------------+ +|SAL |Service |Customer Type | Recommendation | +| |Recovery | | | +| |Time | | | +| |Threshold | | | ++====+===============+======================+====================================+ +|1 |5 - 6 seconds |Network Operator |Redundant resources to be | +| | |Control Traffic |made available on-site to | +| | | |ensure fastrecovery. | +| | |Government/Regulatory | | +| | |Emergency Services | | ++----+---------------+----------------------+------------------------------------+ +|2 |10 - 15 seconds|Enterprise and/or |Redundant resources to be available | +| | |large scale customers |as a mix of on-site and off-site | +| | | |as appropriate: On-site resources to| +| | |Network Operators |be utilized for recovery of | +| | |service traffic |real-time service; Off-site | +| | | |resources to be utilized for | +| | | |recovery of data services | ++----+---------------+----------------------+------------------------------------+ +|3 |20 - 25 seconds|General Consumer |Redundant resources to be mostly | +| | |Public and ISP |available off-site. Real-time | +| | |Traffic |services should be recovered before | +| | | |data services | ++----+---------------+----------------------+------------------------------------+ + +Note that even though SAL 1 of [REL]_ allows for 5-6 seconds of service recovery, +for many services this is too long and such outage causes a service level reset or +the loss of significant amount of data. Also the end-to-end service or network service +may be served by multiple VNFs. Therefore for a single VNF the desired +service recovery time is sub-second. + +Note that failing over the service to another provider entity implies the redirection of the traffic +flow the VNF is handling. This could be achieved in different ways ranging from floating IP addresses +to load balancers. The topic deserves its own investigation, therefore in these first set of +use cases we assume that it is part of the solution without going into the details, which +we will address as a complementary set of use cases. + +.. [REL] ETSI GS NFV-REL 001 V1.1.1 (2015-01) + + +2.1 Use Case 1: VNFC failure in a statefull VNF with redundancy +============================================================== + +Use case 1 represents a statefull VNF with redundancy managed by an HA manager, +which is part of the VNF (Fig 1). The VNF consists of VNFC1, VNFC2 and the HA Manager. +The latter managing the two VNFCs, e.g. the role they play in providing the service +named "Provided NF" (Fig 2). + +The failure happens in one of the VNFCs and it is detected and handled by the HA manager. +On practice the HA manager could be part of the VNFC implementations or it could +be a separate entity in the VNF. The point is that the communication of these +entities inside the VNF is not visible to the rest of the system. The observable +events need to cross the boundary represented by the VNF box. + + +.. figure:: images/Slide4.png + :alt: VNFC failure in a statefull VNF + :figclass: align-center + + Fig 1. VNFC failure in a statefull VNF with built-in HA manager + + +.. figure:: images/StatefullVNF-VNFCfailure.png + :alt: MSC of the VNFC failure in a statefull VNF + :figclass: align-center + + Fig 2. Sequence of events for use case 1 + + +As shown in Fig 2. initially VNFC2 is active, i.e. provides the Provided NF and VNFC1 +is a standby. It is not shown, but it is expected that VNFC1 has some means to get the update +of the state of the Provided NF from the active VNFC2, so that it is prepared to continue to +provide the service in case VNFC2 fails. +The sequence of events starts with the failure of VNFC2, which also interrupts the +Provided NF. This failure is detected somehow and/or reported to the HA Manager, which +in turn may report the failure to the VNFM and simultaneously it tries to isolate the +fault by cleaning up VNFC2. + +Once the cleanup succeeds (i.e. the OK is received) it fails over the active role to +VNFC1 by setting it active. This recovers the service, the Provided NF is indeed +provided again. Thus this point marks the end of the outage caused by the failure +that need to be considered from the perspective of service availability. + +The repair of the failed VNFC2, which might have started at the same time +when VNFC1 was assigned the active state, may take longer but without further impact +on the availability of the Provided NF service. +If the HA Manager reported the interruption of the Provided NF to the VNFM, it should +clear the error condition. + +The key points in this scenario are: + +* The failure of the VNFC2 is not detectable by any other part of the system except + the consumer of the Provided NF. The VNFM only + knows about the failure because of the error report, and only the information this + report provides. I.e. it may or may not include the information on what failed. +* The Provided NF is resumed as soon as VNFC1 is assigned active regardless how long + it takes to repair VNFC2. +* The HA manager could be part of the VNFM as well. This requires an interface to + detect the failures and to manage the VNFC life-cycle and the role assignments. + +2.2 Use Case 2: VM failure in a statefull VNF with redundacy +============================================================ + +Use case 2 also represents a statefull VNF with its redundancy managed by an HA manager, +which is part of the VNF. The VNFCs of the VNF are hosted on the VMs provided by +the NFVI (Fig 3). + +The VNF consists of VNFC1, VNFC2 and the HA Manager (Fig 4). The latter managing +the role the VNFCs play in providing the service - Provided NF. +The VMs provided by the NFVI are managed by the VIM. + + +In this use case it is one of the VMs hosting the VNF fails. The failure is detected +and handled at both the NFVI and the VNF levels simultaneously. The coordination occurs +between the VIM and the VNFM. + + +.. figure:: images/Slide6.png + :alt: VM failure in a statefull VNF + :figclass: align-center + + Fig 3. VM failure in a statefull VNF with built-in HA manager + + +.. figure:: images/StatefullVNF-VMfailure.png + :alt: MSC of the VM failure in a statefull VNF + :figclass: align-center + + Fig 4. Sequence of events for use case 2 + + +Again initially VNFC2 is active and provides the Provided NF, while VNFC1 is the standby. +It is not shown in Fig 4., but it is expected that VNFC1 has some means to learn the state +of the Provided NF from the active VNFC2, so that it is able to continue providing the +service if VNFC2 fails. VNFC1 is hosted on VM1, while VNFC2 is hosted on VM2 as indicated by +the arrows between these objects in Fig 4. + +The sequence of events starts with the failure of VM2, which results in VNFC2 failing and +interrupting the Provided NF. The HA Manager detects the failure of VNFC2 somehow +and tries to handle it the same way as in use case 1. However because the VM is gone the +clean up either not initiated at all or interrupted as soon as the failure of the VM is +identified. In either case the faulty VNFC2 is considered as isolated. + +To recover the service the HA Manager fails over the active role to VNFC1 by setting it active. +This recovers the Provided NF. Thus this point marks again the end of the outage caused +by the VM failure that need to be considered from the perspective of service availability. +If the HA Manager reported the interruption of the Provided NF to the VNFM, it should +clear the error condition. + +On the other hand the failure of the VM is also detected in the NFVI and reported to the VIM. +The VIM reports the VM failure to the VNFM, which passes on this information +to the HA Manager of the VNF. This confirms for the VNF HA Manager the VM failure and that +it needs to wait with the repair of the failed VNFC2 until the VM is provided again. The +VNFM also confirms towards the VIM that it is safe to restart the VM. + +The repair of the failed VM may take some time, but since the service has been failed over +to VNFC1 in the VNF, there is no further impact on the availability of Provided NF. + +When eventually VM2 is restarted the VIM reports this to the VNFM and +the VNFC2 can be restored. + +The key points in this scenario are: + +* The failure of the VM2 is detectable at both levels VNF and NFVI, therefore both the HA + manager and the VIM reacts to it. It is essential that these reactions do not interfere, + e.g. if the VIM tries to protect the VM state at NFVI level that would conflict with the + service failover action at the VNF level. +* While the failure detection happens at both NFVI and VNF levels, the time frame within + which the VIM and the HA manager detect and react may be very different. For service + availability the VNF level detection, i.e. by the HA manager is the critical one and expected + to be faster. +* The Provided NF is resumed as soon as VNFC1 is assigned active regardless how long + it takes to repair VM2 and VNFC2. +* The HA manager could be part of the VNFM as well. + This requires an interface to detect failures in/of the VNFC and to manage its life-cycle and + role assignments. +* The VNFM may not know for sure that the VM failed until the VIM reports it, i.e. whether + the VM failure is due to host, hypervisor, host OS failure. Thus the VIM should report/alarm + and log VM, hypervisor, and physical host failures. The use cases for these failures + are similar with respect to the Provided NF. +* The VM repair also should start with the fault isolation as appropriate for the actual + failed entity, e.g. if the VM failed due to a host failure a host may be fenced first. +* The negotiation between the VNFM and the VIM may be replaced by configured repair actions. + E.g. on error restart VM in initial state, restart VM from last snapshot, or fail VM over to standby. + + +2.3 Use Case 3: VNFC failure in a statefull VNF with no redundancy +================================================================= + +Use case 3 also represents a statefull VNF, but it stores its state externally on a +virtual disk provided by the NFVI. It has a single VNFC and it is managed by the VNFM +(Fig 5). + +In this use case the VNFC fails and the failure is detected and handled by the VNFM. + + +.. figure:: images/Slide10.png + :alt: VNFC failure in a statefull VNF No-Red + :figclass: align-center + + Fig 5. VNFC failure in a statefull VNF with no redundancy + + +.. figure:: images/StatefullVNF-VNFCfailureNoRed.png + :alt: MSC of the VNFC failure in a statefull VNF No-Red + :figclass: align-center + + Fig 6. Sequence of events for use case 3 + + +The VNFC periodically checkpoints the state of the Provided NF to the external storage, +so that in case of failure the Provided NF can be resumed (Fig 6). + +When the VNFC fails the Provided NF is interrupted. The failure is detected by the VNFM +somehow, which to isolate the fault first cleans up the VNFC, then if the cleanup is +successful it restarts the VNFC. When the VNFC starts up, first it reads the last checkpoint +for the Provided NF, then resumes providing it. The service outage lasts from the VNFC failure +till this moment. + +The key points in this scenario are: + +* The service state is saved in an external storage which should be highly available too to + protect the service. +* The NFVI should provide this guarantee and also that storage and access network failures + are handled seemlessly from the VNF's perspective. +* The VNFM has means to detect VNFC failures and manage its life-cycle appropriately. This is + not required if the VNF also provides its availability management. +* The Provided NF can be resumed only after the VNFC is restarted and it has restored the + service state from the last checkpoint created before the failure. +* Having a spare VNFC can speed up the service recovery. This requires that the VNFM coordinates + the role each VNFC takes with respect to the Provided NF. I.e. the VNFCs do not act on the + stored state simultaneously potentially interfering and corrupting it. + + + +2.4 Use Case 4: VM failure in a statefull VNF with no redundancy +=============================================================== + +Use case 4 also represents a statefull VNF without redundancy, which stores its state externally on a +virtual disk provided by the NFVI. It has a single VNFC managed by the VNFM +(Fig 7) as in use case 3. + +In this use case the VM hosting the VNFC fails and the failure is detected and handled by +the VNFM and the VIM simultaneously. + + +.. figure:: images/Slide11.png + :alt: VM failure in a statefull VNF No-Red + :figclass: align-center + + Fig 7. VM failure in a statefull VNF with no redundancy + +.. figure:: images/StatefullVNF-VMfailureNoRed.png + :alt: MSC of the VM failure in a statefull VNF No-Red + :figclass: align-center + + Fig 8. Sequence of events for use case 4 + +Again, the VNFC regularly checkpoints the state of the Provided NF to the external storage, +so that it can be resumed in case of a failure (Fig 8). + +When the VM hosting the VNFC fails the Provided NF is interrupted. + +On the one hand side, the failure is detected by the VNFM somehow, which to isolate the fault tries +to clean the VNFC up which cannot be done because of the VM failure. When the absence of the VM has been +determined the VNFM has to wait with restarting the VNFC until the hosting VM is restored. The VNFM +may report the problem to the VIM, requesting a repair. + +On the other hand the failure is detected in the NFVI and reported to the VIM, which reports it +to the VNFM, if the VNFM hasn't reported it yet. +If the VNFM has requested the VM repair or if it acknowledges the repair, the VIM restarts the VM. +Once the VM is up the VIM reports it to the VNFM, which in turn can restart the VNFC. + +When the VNFC restarts first it reads the last checkpoint for the Provided NF, +to be able to resume it. +The service outage last until this is recovery completed. + +The key points in this scenario are: + + +* The service state is saved in external storage which should be highly available to + protect the service. +* The NFVI should provide such a guarantee and also that storage and access network failures + are handled seemlessly from the perspective of the VNF. +* The Provided NF can be resumed only after the VM and the VNFC are restarted and the VNFC + has restored the service state from the last checkpoint created before the failure. +* The VNFM has means to detect VNFC failures and manage its life-cycle appropriately. Alternatively + the VNF may also provide its availability management. +* The VNFM may not know for sure that the VM failed until the VIM reports this. It also cannot + distinguish host, hypervisor and host OS failures. Thus the VIM should report/alarm and log + VM, hypervisor, and physical host failures. The use cases for these failures are + similar with respect to the Provided NF. +* The VM repair also should start with the fault isolation as appropriate for the actual + failed entity, e.g. if the VM failed due to a host failure a host may be fenced first. +* The negotiation between the VNFM and the VIM may be replaced by configured repair actions. +* VM level redundancy, i.e. running a standby or spare VM in the NFVI would allow faster service + recovery for this use case, but by itself it may not protect against VNFC level failures. I.e. + VNFC level error detection is still required. + + + +2.5 Use Case 5: VNFC failure in a stateless VNF with redundancy +=============================================================== + +Use case 5 represents a stateless VNF with redundancy, i.e. it is composed of VNFC1 and VNFC2. +They are managed by an HA manager within the VNF. The HA manager assigns the active role to provide +the Provided NF to one of the VNFCs while the other remains a spare meaning that it has no state +information for the Provided NF (Fig 9) therefore it could replace any other VNFC capable of +providing the Provided NF service. + +In this use case the VNFC fails and the failure is detected and handled by the HA manager. + + +.. figure:: images/Slide13.png + :alt: VNFC failure in a stateless VNF with redundancy + :figclass: align-center + + Fig 9. VNFC failure in a stateless VNF with redundancy + + +.. figure:: images/StatelessVNF-VNFCfailure.png + :alt: MSC of the VNFC failure in a stateless VNF with redundancy + :figclass: align-center + + Fig 10. Sequence of events for use case 5 + + +Initially VNFC2 provides the Provided NF while VNFC1 is idle or might not even been instantiated +yet (Fig 10). + +When VNFC2 fails the Provided NF is interrupted. This failure is detected by the HA manager, +which as a first reaction cleans up VNFC2 (fault isolation), then it assigns the active role to +VNFC1. It may report an error to the VNFM as well. + +Since there is no state information to recover, VNFC1 can accept the active role right away +and resume providing the Provided NF service. Thus the service outage is over. If the HA manager +reported an error to the VNFM it should clear it at this point. + +The key points in this scenario are: + +* The spare VNFC may be instantiated only once the failure of active VNFC is detected. +* As a result the HA manager's role might be limited to life-cycle management, i.e. no role + assignment is needed if the VNFCs provide the service as soon as they are started up. +* Accordingly the HA management could be part of a generic VNFM provided it is capable of detecting + the VNFC failures. Besides the service users, the VNFC failure may not be detectable at any other + part of the system. +* Also there could be multiple active VNFCs sharing the load of Provided NF and the spare/standby + may protect all of them. +* Reporting the service failure to the VNFM is optional as the HA manager is in charge of recovering + the service and it is aware of the redundancy needed to do so. + + +2.6 Use Case 6: VM failure in a stateless VNF with redundancy +============================================================ + + +Similarly to use case 5, use case 6 represents a stateless VNF composed of VNFC1 and VNFC2, +which are managed by an HA manager within the VNF. The HA manager assigns the active role to +provide the Provided NF to one of the VNFCs while the other remains a spare meaning that it has +no state information for the Provided NF (Fig 11) and it could replace any other VNFC capable +of providing the Provided NF service. + +As opposed to use case 5 in this use case the VM hosting one of the VNFCs fails. This failure is +detected and handled by the HA manager as well as the VIM. + + +.. figure:: images/Slide14.png + :alt: VM failure in a stateless VNF with redundancy + :figclass: align-center + + Fig 11. VM failure in a stateless VNF with redundancy + + +.. figure:: images/StatelessVNF-VMfailure.png + :alt: MSC of the VM failure in a stateless VNF with redundancy + :figclass: align-center + + Fig 12. Sequence of events for use case 6 + + +Initially VNFC2 provides the Provided NF while VNFC1 is idle or might not have been instantiated +yet (Fig 12) as in use case 5. + +When VM2 fails VNFC2 fails with it and the Provided NF is interrupted. The failure is detected by +the HA manager and by the VIM simultaneously and independently. + +The HA manager's first reaction is trying to clean up VNFC2 to isolate the fault. This is considered to +be successful as soon as the disappearance of the VM is confirmed. +After this the HA manager assigns the active role to VNFC1. It may report the error to the VNFM as well +requesting a VM repair. + +Since there is no state information to recover, VNFC1 can accept the assignment right away +and resume the Provided NF service. Thus the service outage is over. If the HA manager reported +an error to the VNFM for the service it should clear it at this point. + +Simultaneously the VM failure is detected in the NFVI and reported to the VIM, which reports it +to the VNFM, if the VNFM hasn't requested a repair yet. If the VNFM requested the VM repair or if +it acknowledges the repair, the VIM restarts the VM. + +Once the VM is up the VIM reports it to the VNFM, which in turn may restart the VNFC if needed. + + +The key points in this scenario are: + +* The spare VNFC may be instantiated only after the detection of the failure of the active VNFC. +* As a result the HA manager's role might be limited to life-cycle management, i.e. no role + assignment is needed if the VNFC provides the service as soon as it is started up. +* Accordingly the HA management could be part of a generic VNFM provided if it is capable of detecting + failures in/of the VNFC and managing its life-cycle. +* Also there could be multiple active VNFCs sharing the load of Provided NF and the spare/standby + may protect all of them. +* The VNFM may not know for sure that the VM failed until the VIM reports this. It also cannot + distinguish host, hypervisor and host OS failures. Thus the VIM should report/alarm and log + VM, hypervisor, and physical host failures. The use cases for these failures are + similar with respect to each Provided NF. +* The VM repair also should start with the fault isolation as appropriate for the actual + failed entity, e.g. if the VM failed due to a host failure a host needs to be fenced first. +* The negotiation between the VNFM and the VIM may be replaced by configured repair actions. +* Reporting the service failure to the VNFM is optional as the HA manager is in charge recovering + the service and it is aware of the redundancy needed to do so. + + + +2.7 Use Case 7: VNFC failure in a stateless VNF with no redundancy +================================================================== + +Use case 7 represents a stateless VNF composed of a single VNFC, i.e. with no redundancy. +The VNF and in particular its VNFC is managed by the VNFM through managing its life-cycle (Fig 13). + +In this use case the VNFC fails. This failure is detected and handled by the VNFM. This use case +requires that the VNFM can detect the failures in the VNF or they are reported to the VNFM. + +The failure is only detectable at the VNFM level and it is handled by the VNFM restarting the VNFC. + + +.. figure:: images/Slide16.png + :alt: VNFC failure in a stateless VNF with no redundancy + :figclass: align-center + + Fig 13. VNFC failure in a stateless VNF with no redundancy + + +.. figure:: images/StatelessVNF-VNFCfailureNoRed.png + :alt: MSC of the VNFC failure in a stateless VNF with no redundancy + :figclass: align-center + + Fig 14. Sequence of events for use case 7 + +The VNFC is providing the Provided NF when it fails (Fig 14). This failure is detected or reported to +the VNFM, which has to clean up the VNFC to isolate the fault. After cleanup success it can proceed +with restarting the VNFC, which as soon as it is up it starts to provide the Provided NF +as there is no state to recover. + +Thus the service outage is over, but it has included the entire time needed to restart the VNFC. +Considering that the VNF is stateless this may not be significant still. + + +The key points in this scenario are: + +* The VNFM has to have the means to detect VNFC failures and manage its life-cycle appropriately. + This is not required if the VNF comes with its availability management, but this is very unlikely + for such stateless VNFs. +* The Provided NF can be resumed as soon as the VNFC is restarted, i.e. the restart time determines + the outage. +* In case multiple VNFCs are used they should not interfere with one another, they should + operate independently. + + +2.8 Use Case 8: VM failure in a stateless VNF with no redundancy +================================================================ + +Use case 8 represents the same stateless VNF composed of a single VNFC as use case 7, i.e. with +no redundancy. The VNF and in particular its VNFC is managed by the VNFM through managing its +life-cycle (Fig 15). + +In this use case the VM hosting the VNFC fails. This failure is detected and handled by the VNFM +as well as by the VIM. + + +.. figure:: images/Slide17.png + :alt: VM failure in a stateless VNF with no redundancy + :figclass: align-center + + Fig 15. VM failure in a stateless VNF with no redundancy + + +.. figure:: images/StatelessVNF-VMfailureNoRed.png + :alt: MSC of the VM failure in a stateless VNF with no redundancy + :figclass: align-center + + Fig 16. Sequence of events for use case 8 + +The VNFC is providing the Provided NF when the VM hosting the VNFC fails (Fig 16). + +This failure may be detected or reported to the VNFM as a failure of the VNFC. The VNFM may +not be aware at this point that it is a VM failure. Accordingly its first reaction as in use case 7 +is to clean up the VNFC to isolate the fault. Since the VM is gone, this cannot succeed and the VNFM +becomes aware of the VM failure through this or it is reported by the VIM. In either case it has to wait +with the repair of the VMFC until the VM becomes available again. + +Meanwhile the VIM also detects the VM failure and reports it to the VNFM unless the VNFM has already +requested the VM repair. After the VNFM confirming the VM repair the VIM restarts the VM and reports +the successful repair to the VNFM, which in turn can start the VNFC hosted on it. + + +Thus the recovery of the Provided NF includes the restart time of the VM and of the VNFC. + +The key points in this scenario are: + +* The VNFM has to have the means to detect VNFC failures and manage its life-cycle appropriately. + This is not required if the VNF comes with its availability management, but this is very unlikely + for such stateless VNFs. +* The Provided NF can be resumed only after the VNFC is restarted on the repaired VM, i.e. the + restart time of the VM and the VNFC determines the outage. +* In case multiple VNFCs are used they should not interfere with one another, they should + operate independently. +* The VNFM may not know for sure that the VM failed until the VIM reports this. It also cannot + distinguish host, hypervisor and host OS failures. Thus the VIM should report/alarm and log + VM, hypervisor, and physical host failures. The use cases for these failures are + similar with respect to each Provided NF. +* The VM repair also should start with the fault isolation as appropriate for the actual + failed entity, e.g. if the VM failed due to a host failure the host needs to be fenced first. +* The repair negotiation between the VNFM and the VIM may be replaced by configured repair actions. +* VM level redundancy, i.e. running a standby or spare VM in the NFVI would allow faster service + recovery for this use case, but by itself it may not protect against VNFC level failures. I.e. + VNFC level error detection is still required. + +2.9 Use Case 9: Repeated VNFC failure in a stateless VNF with no redundancy +=========================================================================== + +Finally use case 9 represents again a stateless VNF composed of a single VNFC as in use case 7, i.e. +with no redundancy. The VNF and in particular its VNFC is managed by the VNFM through managing its +life-cycle. + +In this use case the VNFC fails repeatedly. This failure is detected and handled by the VNFM, +but results in no resolution of the fault (Fig 17) because the VNFC is manifesting a fault, +which is not in its scope. I.e. the fault is propagating to the VNFC from a faulty VM or host, +for example. Thus the VNFM cannot resolve the problem by itself. + + +.. figure:: images/Slide19.png + :alt: Repeated VNFC failure in a stateless VNF with no redundancy + :figclass: align-center + + Fig 17. VM failure in a stateless VNF with no redundancy + + +To handle this case the failure handling needs to be escalated to the a bigger fault zone +(or fault domain), i.e. a scope within which the faults may propagate and manifest. In case of the +VNF the bigger fault zone is the VM and the facilities hosting it, all managed by the VIM. + +Thus the VNFM should request the repair from the VIM (Fig 18). + +Since the VNFM is only aware of the VM, it needs to report an error on the VM and it is the +VIM's responsibility to sort out what might be the scope of the actual fault depending on other +failures and error reports in its scope. + + +.. figure:: images/Slide20.png + :alt: Escalation of repeated VNFC failure in a stateless VNF with no redundancy + :figclass: align-center + + Fig 18. VM failure in a stateless VNF with no redundancy + + +.. figure:: images/StatelessVNF-VNFCfailureNoRed-Escalation.png + :alt: MSC of the VM failure in a stateless VNF with no redundancy + :figclass: align-center + + Fig 19. Sequence of events for use case 9 + + +This use case starts similarly to use case 7, i.e. the VNFC is providing the Provided NF when it fails +(Fig 17). +This failure is detected or reported to the VNFM, which cleans up the VNFC to isolate the fault. +After successful cleanup the VNFM proceeds with restarting the VNFC, which as soon as it is up +starts to provide the Provided NF again as in use case 7. + +However the VNFC failure occurs N times repeatedly within some Probation time for which the VNFM starts +the timer when it detects the first failure of the VNFC. When the VNFC fails once more still within the +probation time the Escalation counter maximum is exceeded and the VNFM reports an error to the VIM on +the VM hosting the VNFC as obviously cleaning up and restarting the VNFC did not solve the problem. + +When the VIM receives the error report for the VM it has to isolate the fault by cleaning up at least +the VM. After successful cleanup it can restart the VM and once it is up report the VM repair to the VNFM. +At this point the VNFM can restart the VNFC, which in turn resumes the Provided VM. + +In this scenario the VIM needs to evaluate what may be the scope of the fault to determine what entity +needs a repair. For example, if it has detected VM failures on that same host, or other VNFMs +reported errors on VMs hosted on the same host, it should consider that the entire host needs a repair. + + +The key points in this scenario are: + +* The VNFM has to have the means to detect VNFC failures and manage its life-cycle appropriately. + This is not required if the VNF comes with its availability management, but this is very unlikely + for such stateless VNFs. +* The VNFM needs to correlate VNFC failures over time to be able to detect failure of a bigger fault zone. + One way to do so is through counting the failures within a probation time. +* The VIM cannot detect all failures caused by faults in the entities under its control. It should be + able to receive error reports and correlate these error reports based on the dependencies + of the different entities. +* The VNFM does not know the source of the failure, i.e. the faulty entity. +* The VM repair should start with the fault isolation as appropriate for the actual + failed entity, e.g. if the VM failed due to a host failure the host needs to be fenced first. + +******************** +3 Concluding remarks +******************** + +This use case document outlined the model and some failure modes for NFV systems. These are an +initial list. The OPNFV HA project team is continuing to grow the list of use cases and will +issue additional documents going forward. The basic use cases and service availability considerations +help define the key considerations for each use case taking into account the impact on the end service. +The use case document along with the requirements documents and gap analysis help set context for +engagement with various upstream projects. diff --git a/Scenario_Seperate_Sections/Section_3_Communication_Interfaces.rst b/Scenario_Seperate_Sections/Section_3_Communication_Interfaces.rst new file mode 100644 index 0000000..c97776b --- /dev/null +++ b/Scenario_Seperate_Sections/Section_3_Communication_Interfaces.rst @@ -0,0 +1,80 @@ +3. Communication Interfaces for VNF HA schemes +=========================================================== + +This section will discuss some general issues about communication interfaces +in the VNF HA schemes. In sections 2, the usecases of both stateful and +stateless VNFs are discussed. While in this section, we would like to discuss +some specific issues which are quite general for all the usecases proposed +in the previous sections. + +3.1. VNF External Interfaces + +Regardless whether the VNF is stateful or stateless, all the VNFCs should act as +a union from the perspective of the outside world. That means all the VNFCs should +share a common interface where the outside modules (e.g., the other VNFs) can +access the service from. There could be multiple solutions for this share of IP +interface. However, all of this sharing and switching of IP address should be +ignorant to the outside modules. + +There are several approaches for the VNFs to share the interfaces. A few of them +are listed as follows and will be discussed in detail. + +1) IP address of VMs for active/stand-by VM. + +2) Load balancers for active/active use cases + +Note that combinition of these two approaches is also feasible. + +For active/standby VNFCs, there is a common IP address shared by the VMs hosting +the active and standby VNFCs, so that they look as one instance from outside. +The HA manager will manage the assignment of the IP address to the VMs. +(The HA manager may not be aware of this, I.e. the address may be configured +and the active/standby state management is linked to the possession of the IP +address, i.e. the active VNFC claims it as part of becoming active.) Only the +active one possesses the IP address. And when failover happens, the standby +is set to be active and can take possession of the IP address to continue traffic +process. + + +For active/active VNFCs, a LB(Load Balancer) could be used. In such scenario, there +could be two cases for the deployment and usage of LB. + +Case 1: LB used in front of a cluster of VNFCs to distribute the traffic flow. + +In such case, the LB is deployed in front of a cluster of multiple VNFCs. Such +cluster can be managed by a seperate cluster manager, or can be managed just +by the LB, which uses heartbeat to monitor each VNFC. When one of VNFCs fails, +the cluster manager should first exclude the failed VNFC from the cluster so that +the LB will re-route the traffic to the other VNFCs, and then the failed one should +be recovered. In the case when the LB is acting as the cluster manager, it is +the LB's responsibility to inform the VNFM to recover the failed VNFC if possible. + + +Case 2: LB used in front of a cluster of VMs to distribute traffic flow. + +In this case, there exists a cluster manager(e.g. Pacemaker) to monitor and manage +the VMs in the cluster. The LB sits in front of the VM cluster so as to distribute +the traffic. When one of the VM fails, the cluster manager will detect that and will +be in charge of the recovery. The cluster manager will also exclude the failed VM +out of the cluster, so that the LB won't route traffic to the failed one. + +In both two cases, the HA of the LB should also be considered. + + +3.2. Intra-VNF Communication + +For stateful VNFs, data synchronization is necessary between the active and standby VMs. +The HA manager is responsible for handling VNFC failover, and do the assignment of the +active/standby states between the VNFCs of the VNF. Data synchronization can be handled +either by the HA manager or by the VNFC itself. + +The state synchronization can happen as + +- direct communication between the active and the standby VNFCs + +- based on the information received from the HA manager on channel or messages using a common queue, + +- it could be through a shared storage assigned to the whole VNF + +- through the checkpointing of state information via underlying memory and/or +database checkpointing services to a separate VM and storage repository. diff --git a/Scenario_Seperate_Sections/Section_4_UseCases_for_Network_Nodes.rst b/Scenario_Seperate_Sections/Section_4_UseCases_for_Network_Nodes.rst new file mode 100644 index 0000000..bc9266a --- /dev/null +++ b/Scenario_Seperate_Sections/Section_4_UseCases_for_Network_Nodes.rst @@ -0,0 +1,157 @@ +4 High Availability Scenarios for Network Nodes +=============================================== + +4.1 Network nodes and HA deployment +----------------------------------- + +OpenStack network nodes contain: Neutron DHCP agent, Neutron L2 agent, Neutron L3 agent, Neutron LBaaS +agent and Neutron Metadata agent. The DHCP agent provides DHCP services for virtual networks. The +metadata agent provides configuration information such as credentials to instances. Note that the +L2 agent cannot be distributed and highly available. Instead, it must be installed on each data +forwarding node to control the virtual network drivers such as Open vSwitch or Linux Bridge. One L2 +agent runs per node and controls its virtual interfaces. + +A typical HA deployment of network nodes can be achieved in Fig 20. Here shows a two nodes cluster. +The number of the nodes is decided by the size of the cluster. It can be 2 or more. More details can be +achieved from each agent's part. + + +.. figure:: images_network_nodes/Network_nodes_deployment.png + :alt: HA deployment of network nodes + :figclass: align-center + + Fig 20. A typical HA deployment of network nodes + + +4.2 DHCP agent +-------------- + +The DHCP agent can be natively highly available. Neutron has a scheduler which lets you run multiple +agents across nodes. You can configure the dhcp_agents_per_network parameter in the neutron.conf file +and set it to X (X >=2 for HA, default is 1). + +If the X is set to 2, as depicted in Fig 21 three tenant networks (there can be multiple tenant networks) +are used as an example, six DHCP agents are deployed in two nodes for three networks, they are +all active. Two dhcp1s serve one network, dhcp2s and dhcp3s serve other two different networks. In a +network, all DHCP traffic is broadcast, DHCP servers race to offer IP. All the servers will update the +lease tables. In Fig 22, when the agent(s) in Node1 doesn't work which can be caused by software +failure or hardware failure, the dhcp agent(s) on Node2 will continue to offer IP for the network. + + +.. figure:: images_network_nodes/DHCP_deployment.png + :alt: HA deployment of DHCP agents + :figclass: align-center + + Fig 21. Natively HA deployment of DHCP agents + + +.. figure:: images_network_nodes/DHCP_failure.png + :alt: Failure of DHCP agents + :figclass: align-center + + Fig 22. Failure of DHCP agents + + +4.3 L3 agent +------------ + +The L3 agent is also natively highly available. To achieve HA, it can be configured in the neutron.conf +file. + +.. code-block:: bash + + l3_ha = True # All routers are highly available by default + + allow_automatic_l3agent_failover = True # Set automatic L3 agent failover for routers + + max_l3_agents_per_router = 2 # Maximum number of network nodes to use for the HA router + + min_l3_agents_per_router = 2 # Minimum number of network nodes to use for the HA router. A new router + can be created only if this number of network nodes are available. + +According to the neutron.conf file, the L3 agent scheduler supports Virtual Router Redundancy +Protocol (VRRP) to distribute virtual routers across multiple nodes (e.g. 2). The scheduler will choose +a number between the maximum and the minimum number according scheduling algorithm. VRRP is implemented +by Keepalived. + +As depicted in Fig 23, both L3 agents in Node1 and Node2 host vRouter 1 and vRouter 2. In Node 1, +vRouter 1 is active and vRouter 2 is standby (hot standby). In Node2, vRouter 1 is standby and +vRouter 2 is active. For the purpose of reducing the load, two actives are deployed in two Nodes +alternatively. In Fig 24, Keepalived will be used to manage the VIP interfaces. One instance of +keepalived per virtual router, then one per namespace. 169.254.192.0/18 is a dedicated HA network +which is created in order to isolate the administrative traffic from the tenant traffic, each vRouter +will be connected to this dedicated network via an HA port. More details can be achieved from the +Reference at the bottom. + + +.. figure:: images_network_nodes/L3_deployment.png + :alt: HA deployment of L3 agents + :figclass: align-center + + Fig 23. Natively HA deployment of L3 agents + + +.. figure:: images_network_nodes/L3_ha_principle.png + :alt: HA principle of L3 agents + :figclass: align-center + + Fig 24. Natively HA principle of L3 agents + + +In Fig 25, when vRouter 1 in Node1 is down which can be caused by software failure or hardware failure, +the Keepalived will detect the failure and the standby will take over to be active. In order to keep the +TCP connection, Conntrackd is used to maintain the TCP sessions going through the router. One instance +of conntrackd per virtual router, then one per namespace. After then, a rescheduling procedure will be +triggered to respawn the failed virtual router to another l3 agent as standby. All the workflows is +depicted in Fig 26. + + +.. figure:: images_network_nodes/L3_failure.png + :alt: Failure of L3 agents + :figclass: align-center + + Fig 25. Failure of L3 agents + + +.. figure:: images_network_nodes/L3_ha_workflow.png + :alt: HA workflow of L3 agents + :figclass: align-center + + Fig 26. HA workflow of L3 agents + + +4.4 LBaaS agent and Metadata agent +---------------------------------- + +Currently, no native feature is provided to make the LBaaS agent highly available using the defaul +plug-in HAProxy. A common way to make HAProxy highly available is to use Pacemaker. + + +.. figure:: images_network_nodes/LBaaS_deployment.png + :alt: HA deployment of LBaaS agents + :figclass: align-center + + Fig 27. HA deployment of LBaaS agents using Pacemaker + + +As shown in Fig 27 HAProxy and pacemaker are deployed in both of the network nodes. The number of network +nodes can be 2 or more. It depends on your cluster. HAProxy in Node 1 is the master and the VIP is in +Node 1. Pacemaker monitors the liveness of HAProxy. + + +.. figure:: images_network_nodes/LBaaS_failure.png + :alt: Failure of LBaaS agents + :figclass: align-center + + Fig 28. Failure of LBaaS agents + + +As shown in Fig 28 when HAProxy in Node1 falls down which can be caused by software failure or hardware +failure, Pacemaker will fail over HAProxy and the VIP to Node 2. + +Note that the default plug-in HAProxy only supports TCP and HTTP. + +No native feature is available to make Metadata agent highly available. At this time, the Active/Passive +solution exists to run the neutron metadata agent in failover mode with Pacemaker. The deployment and +failover procedure can be the same as the case of LBaaS. + diff --git a/Scenario_Seperate_Sections/Section_5_Storage-HA-Scenarios.rst b/Scenario_Seperate_Sections/Section_5_Storage-HA-Scenarios.rst new file mode 100644 index 0000000..b8b37a3 --- /dev/null +++ b/Scenario_Seperate_Sections/Section_5_Storage-HA-Scenarios.rst @@ -0,0 +1,442 @@ +Storage and High Availability Scenarios +======================================= + +5.1 Elements of HA Storage Management and Delivery +-------------------------------------------------- + +Storage infrastructure, in any environment, can be broken down into two +domains: Data Path and Control Path. Generally, High Availability of the +storage infrastructure is measured by the occurence of Data +Unavailability and Data Loss (DU/DL) events. While that meaning is +obvious as it relates to the Data Path, it is also applicable to Control +Path as well. The inability to attach a volume that has data to a host, +for example, can be considered a Data Unavailability event. Likewise, +the inability to create a volume to store data could be considered Data +Loss since it may result in the inability to store critical data. + +Storage HA mechanisms are an integral part of most High Availability +solutions today. In the first two sections below, we define the +mechanisms of redundancy and protection required in the infrastructure +for storage delivery in both the Data and Control Paths. Storage +services that have these mechanisms can be used in HA environments that +are based on a highly available storage infrastructure. + +In the third section below, we examine HA implementations that rely on +highly available storage infrastructure. Note that the scope throughout this +section is focused on local HA solutions. This does not address rapid remote +Disaster Recovery scenarios that may be provided by storage, nor +does it address metro active/active environments that implement stretched +clusters of hosts across multiple sites for workload migration and availability. + + +5.2 Storage Failure & Recovery Scenarios: Storage Data Path +----------------------------------------------------------- + +In the failure and recovery scenarios described below, a redundant +network infrastructure provides HA through network-related device +failures, while a variety of strategies are used to reduce or minimize +DU/DL events based on storage system failures. This starts with redundant +storage network paths, as shown in Figure 29. + +.. figure:: StorageImages/RedundantStoragePaths.png + :alt: HA Storage Infrastructure + :figclass: align-center + + Figure 29: Typical Highly Available Storage Infrastructure + +Storage implementations vary tremendously, and the recovery mechanisms +for each implementation will vary. These scenarios described below are +limited to 1) high level descriptions of the most common implementations +since it is unpredictable as to +which storage implementations may be used for NFVI; 2) HW- and +SW-related failures (and recovery) of the storage data path, and not +anything associated with user configuration and operational issues which +typically create the most common storage failure scenarios; 3) +non-LVM/DAS based storage implementations(managing failure and recovery +in LVM-based storage for OpenStack is a very different scenario with +less of a reliable track record); and 4) I will assume block storage +only, and not object storage, which is often used for stateless +applications (at a high level, object stores may include a +subset of the block scenarios under the covers). + +To define the requirements for the data path, I will start at the +compute node and work my way down the storage IO stack and touch on both +HW and SW failure/recovery scenarios for HA along the way. I will use Figure 1 as a reference. + +1. Compute IO driver: Assuming iSCSI for connectivity between the +compute and storage, an iSCSI initiator on the compute node maintains +redundant connections to multiple iSCSI targets for the same storage +service. These redundant connections may be aggregated for greater +throughput, or run independently. This redundancy allows the iSCSI +Initiator to handle failures in network connectivity from compute to +storage infrastructure. (Fibre Channel works largely the same way, as do +proprietary drivers that connect a host's IO stack to storage systems). + +2. Compute node network interface controller (NIC): This device may +fail, and said failure reported via whatever means is in place for such +reporting from the host.The redundant paths between iSCSI initiators and +targets will allow connectivity from compute to storage to remain up, +though operating at reduced capacity. + +3. Network Switch failure for storage network: Assuming there are +redundant switches in place, and everything is properly configured so +that two compute NICs go to two separate switches, which in turn go to +two different storage controllers, then a switch may fail and the +redundant paths between iSCSI initiators and targets allows connectivity +from compute to storage to operational, though operating at reduced +capacity. + +4. Storage system network interface failure: Assuming there are +redundant storage system network interfaces (on separate storage +controllers), then one may fail and the redundant paths between iSCSI +initiators and targets allows connectivity from compute to storage to +remain operational, though operating at reduced performance. The extent +of the reduced performance is dependent upon the storage architecture. +See 3.5 for more. + +5. Storage controller failure: A storage system can, at a very high +level, be described as composed of network interfaces, one or more +storage controllers that manage access to data, and a shared Data Path +access to the HDD/SSD subsystem. The network interface failure is +described in #4, and the HDD/SSD subsystem is described in #6. All +modern storage architectures have either redundant or distributed +storage controller architectures. In **dual storage controller +architectures**, high availability is maintained through the ALUA +protocol maintaining access to primary and secondary paths to iSCSI +targets. Once a storage controller fails, the array operates in +(potentially) degraded performance mode until the failed storage controller is +replaced. The degree of reduced performance is dependent on the overall +original load on the array. Dual storage controller arrays also remain at risk +of a Data Unavailability event if the second storage controller should fail. +This is rare, but should be accounted for in planning support and +maintenance contracts. + +**Distributed storage controller architectures** are generally server-based, +which may or may not operate on the compute servers in Converged +Infrastructure environments. Hence the concept of “storage controller” +is abstract in that it may involve a distribution of software components +across multiple servers. Examples: Ceph and ScaleIO. In these environments, +the data may be stored +redundantly, and metadata for accessing the data in these redundant +locations is available for whichever compute node needs the data (with +authorization, of course). Data may also be stored using erasure coding +(EC) for greater efficiency. The loss of a storage controller in this +context leads to a discussion of impact caused by loss of a server in +this distributed storage controller architecture. In the event of such a loss, +if data is held in duplicate or triplicate on other servers, then access +is simply redirected to maintain data availability. In the case of +EC-based protection, then the data is simply re-built on the fly. The +performance and increased risk impact in this case is dependent on the +time required to rebalance storage distribution across other servers in +the environment. Depending on configuration and implementation, it could +impact storage access performance to VNFs as well. + +6. HDD/SSD subsystem: This subsystem contains any RAID controllers, +spinning hard disk drives, and Solid State Drives. The failure of a RAID +controller is equivalent to failure of a storage controller, as +described in 5 above. The failure of one or more storage devices is +protected by either RAID parity-based protection, Erasure Coding +protection, or duplicate/triplicate storage of the data. RAID and +Erasure Coding are typically more efficient in terms of space +efficiency, but duplicate/triplicate provides better performance. This +tradeoff is a common point of contention among implementations, and this +will not go into greater detail than to assume that failed devices do +not cause Data Loss events due to these protection algorithms. Multiple +device failures can potentially cause Data Loss events, and the risk of +each method must be taken into consideration for the HA requirements of +the desired deployment. + +5.3 Storage Failure & Recovery Scenarios: Storage Control Path +-------------------------------------------------------------- + +As it relates to an NFVI environment, as proposed by OPNFV, there are +two parts to the storage control path. + +* The storage system-specific control path to the storage controller + +* The OpenStack-specific cloud management framework for managing different +storage elements + + +5.3.1 Storage System Control Paths +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +High Availability of a storage controller is storage +system-specific. Breaking it down to implementation variants is the best +approach. However, both variants assume an IP-based management API in +order to leverage network redundancy mechanisms for ubiquitous +management access. + +An appliance style storage array with dual storage controllers must implement IP +address failover for the management API's IP endpoint in either an +active/active or active/passive configuration. Likewise, a storage array +with >2 storage controllers would bring up a management endpoint on +another storage controller in such an event. Cluster-style IP address load +balancing is also a viable implementation in these scenarios. + +In the case of distributed storage controller architectures, the storage system +provides redundant storage controller interfaces. E.g., Ceph's RADOS provides +redundant paths to access an OSD for volume creation or access. In EMC's +ScaleIO, there are redundant MetaData Managers for managing volume +creation and access. In the case of the former, the access is via +proprietary protocol, in the case of the latter, it is via HTTP-based +REST API. Other storage implementations may also provide alternative +methods, but any enterprise-class storage system will have built-in HA +for management API access. + +Finally, note that single server-based storage solutions, such as LVM, +do not have HA solutions for control paths. If the server is failed, the +management of that server's storage is not available. + +5.3.2 OpenStack Controller Management +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +OpenStack cloud management is comprised of a number of different +function-specific management modules such as Keystone for Identity and +Access management (IAM), Nova for compute management, Cinder for block +storage management, Swift for Object Storage delivery, Neutron for +Network management, and Glance as an image repository. In smaller +single-cloud environments, these management systems are managed in +concert for High Availability; in larger multi-cloud environments, the +Keystone IAM may logically stand alone in its own HA delivery across the +multiple clouds, as might Swift as a common Object Store. Nova, Cinder, +and Glance may have separate scopes of management, but they are more +typically managed together as a logical cloud deployment. + +It is the OpenStack deployment mechanisms that are responsible for HA +deployment of these HA management infrastructures. These tools, such as +Fuel, RDO, and others, have matured to include highly available +implementations for the database, the API, and each of the manager +modules associated with the scope of cloud management domains. + +There are many interdependencies among these modules that impact Cinder high availability. +For example: + +* Cinder is implemented as an Active/Standby failover implementation since it +requires a single point of control at one time for the Cinder manager/driver implementation. +The Cinder manager/driver is deployed on two of the three OpenStack controller nodes, and +one is made active while the other is passive. This may be improved to active/active +in a future release. + +* A highly available database implementation must be delivered +using something like MySQL/Galera replication across the 3 OpenStack controller +nodes. Cinder requires an HA database in order for it to be HA. + +* A redundant RabbitMQ messaging implementation across the same +three OpenStack controller nodes. Likewise, Cinder requires an HA messaging system. + +* A redundant OpenStack API to ensure Cinder requests can be delivered. + +* An HA Cluster Manager, like PaceMaker for monitoring each of the +deployed manager elements on the OpenStack controllers, with restart capability. +Keepalived is an alternative implementation for monitoring processes and restarting on +alternate OpenStack controller nodes. While statistics are lacking, it is generally +believed that the PaceMaker implementation is more frequently implemented +in HA environments. + + +For more information on OpenStack and Cinder HA, see http://docs.openstack.org/ha-guide +for current thinking. + +While the specific combinations of management functions in these +redundant OpenStack controllers may vary with the specific small/large environment +deployment requirements, the basic implementation of three OpenStack controller +redundancy remains relatively common. In these implementations, the +highly available OpenStack controller environment provides HA access to +the highly available storage controllers via the highly available IP +network. + + +5.4 The Role of Storage in HA +----------------------------- + +In the sections above, we describe data and control path requirements +and example implementations for delivery of highly available storage +infrastructure. In summary: + +* Most modern storage infrastructure implementations are inherently +highly available. Exceptions certainly apply; e.g., simply using LVM for +storage presentation at each server does not satisfy HA requirements. +However, modern storage systems such as Ceph, ScaleIO, XIV, VNX, and +many others with OpenStack integrations, certainly do have such HA +capabilities. + +* This is predominantly through network-accessible shared storage +systems in tightly coupled configurations such as clustered hosts, or in +loosely coupled configurations such as with global object stores. + + +Storage is an integral part of HA delivery today for applications, +including VNFs. This is examined below in terms of using storage as a +key part of HA delivery, the possible scope and limitations of that +delivery, and example implementations for delivery of such service. We +will examine this for both block and object storage infrastructures below. + +5.4.1 VNF, VNFC, and VM HA in a Block Storage HA Context +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Several scenarios were described in another section with regard to +managing HA at the VNFC level, with variants of recovery based on either +VIM- or VNFM-based reporting/detection/recovery mechanisms. In a block +storage environment, these differentiations are abstract and +meaningless, regardless of whether it is or is not intended to be HA. + +In a block storage context, HA is delivered via a logical block device +(sometimes called a Logical Unit, or LUN), or in some cases, to a VM. +VM and logical block devices are the units of currency. + +.. figure:: StorageImages/HostStorageCluster.png + :alt: Host Storage Cluster + :figclass: align-center + + Figure 30: Typical HA Cluster With Shared Storage + +In Figure 30, several hosts all share access, via an IP network +or via Fibre Channel, to a common set of logical storage devices. In an +ESX cluster implementation, these hosts all access all devices with +coordination provided with the SCSI Reservation mechanism. In the +particular ESX case, the logical storage devices provided by the storage +service actually aggregate volumes (VMDKs) utilized by VMs. As a result, +multiple host access to the same storage service logical device is +dynamic. The vSphere management layer provides for host cluster +management. + +In other cases, such as for KVM, cluster management is not formally +required, per se, because each logical block device presented by the +storage service is uniquely allocated for one particular VM which can +only execute on a single host at a time. In this case, any host that can +access the same storage service is potentially a part of the "cluster". +While *potential* access from another host to the same logical block +device is necessary, the actual connectivity is restricted to one host +at a time. This is more of a loosely coupled cluster implementation, +rather than the tightly coupled cluster implementation of ESX. + +So, if a single VNF is implemented as a single VM, then HA is provided +by allowing that VM to execute on a different host, with access to the +same logical block device and persistent data for that VM, located on +the storage service. This also applies to multiple VNFs implemented +within a single VM, though it impacts all VNFs together. + +If a single VNF is implemented across multiple VMs as multiple VNFCs, +then all of the VMs that comprise the VNF may need to be protected in a consistent +fashion. The storage service is not aware of the +distinction from the previous example. However, a higher level +implementation, such as an HA Manager (perhaps implemented in a VNFM) +may monitor and restart a collection of VMs on alternate hosts. In an ESX environment, +VM restarts are most expeditiously handled by using vSphere-level HA +mechanisms within an HA cluster for individual or collections of VMs. +In KVM environments, a separate HA +monitoring service, such as Pacemaker, can be used to monitor individual +VMs, or entire multi-VM applications, and provide restart capabilities +on separately configured hosts that also have access to the same logical +storage devices. + +VM restart times, however, are measured in 10's of seconds. This may +sometimes meet the SAL-3 recovery requirements for General Consumer, +Public, and ISP Traffic, but will never meet the 5-6 seconds required +for SAL-1 Network Operator Control and Emergency Services. For this, +additional capabilities are necessary. + +In order to meet SAL-1 restart times, it is necessary to have: 1. A hot +spare VM already up and running in an active/passive configuration 2. +Little-to-no-state update requirements for the passive VM to takeover. + +Having a spare VM up and running is easy enough, but putting that VM in +an appropriate state to take over execution is the difficult part. In shared storage +implementations for Fault Tolerance, which can achieve SAL-1 requirements, +the VMs share access to the same storage device, and another wrapper function +is used to update internal memory state for every interaction to the active +VM. + +This may be done in one of two ways, as illustrated in Figure 31. In the first way, +the hypervisor sends all interface interactions to the passive as well +as the active VM. The interaction is handled completely by +hypervisor-to-hypervisor wrappers, as represented by the purple box encapsulating +the VM in Figure 31, and is completely transparent to the VM. +This is available with the vSphere Fault Tolerant option, but not with +KVM at this time. + +.. figure:: StorageImages/FTCluster.png + :alt: FT host and storage cluster + :figclass: align-center + + Figure 31: A Fault Tolerant Host/Storage Configuration + +In the second way, a VM-level wrapper is used to capture checkpoints of +state from the active VM and transfers these to the passive VM, similarly represented +as the purple box encapsulating the VM in Figure 3. There +are various levels of application-specific integration required for this +wrapper to capture and transfer checkpoints of state, depending on the +level of state consistency required. OpenSAF is an example of an +application wrapper that can be used for this purpose. Both techniques +have significant network bandwidth requirements and may have certain +limitations and requirements for implementation. + +In both cases, the active and passive VMs share the same storage infrastructure. +Although the OpenSAF implementation may also utilize separate storage infrastructure +as well (not shown in Figure 3). + +Looking forward to the long term, both of these may be made obsolete. As soon as 2016, +PCIe fabrics will start to be available that enable shared NVMe-based +storage systems. While these storage systems may be used with +traditional protocols like SCSI, they will also be usable with true +NVMe-oriented applications whose memory state are persisted, and can be +shared, in an active/passive mode across hosts. The HA mechanisms here +are yet to be defined, but will be far superior to either of the +mechanisms described above. This is still a future. + + +5.4.2 HA and Object stores in loosely coupled compute environments +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Whereas block storage services require tight coupling of hosts to +storage services via SCSI protocols, the interaction of applications +with HTTP-based object stores utilizes a very loosely coupled +relationship. This means that VMs can come and go, or be organized as an +N+1 redundant deployment of VMs for a given VNF. Each individual object +transaction constitutes the duration of the coupling, whereas with +SCSI-based logical block devices, the coupling is active for the +duration of the VM's mounting of the device. + +However, the requirement for implementation here is that the state of a +transaction being performed is made persistent to the object store by +the VM, as the restartable checkpoint for high availability. Multiple +VMs may access the object store somewhat simultaneously, and it is +required that each object transaction is made idempotent by the +application. + +HA restart of a transaction in this environment is dependent on failure +detection and transaction timeout values for applications calling the +VNFs. These may be rather high and even unachievable for the SAL +requirements. For example, while the General Consumer, Public, and ISP +Traffic recovery time for SAL-3 is 20-25 seconds, default browser +timeouts are upwards of 120 seconds. Common default timeouts for +applications using HTTP are typically around 10 seconds or higher +(browsers are upward of 120 seconds), so this puts a requirement on the +load balancers to manage and restart transactions in a timeframe that +may be a challenge to meeting even SAL-3 requirements. + +Despite these issues of performance, the use of object storage for highly +available solutions in native cloud applications is very powerful. Object +storage services are generally globally distributed and replicated using +eventual consistency techniques, though transaction-level consistency can +also be achieved in some cases (at the cost of performance). (For an interesting +discussion of this, lookup the CAP Theorem.) + + +5.5 Summary +----------- + +This section addressed several points: + +* Modern storage systems are inherently Highly Available based on modern and reasonable +implementations and deployments. + +* Storage is typically a central component in offering highly available infrastructures, +whether for block storage services for traditional applications, or through object +storage services that may be shared globally with eventual consistency. + +* Cinder HA management capabilities are defined and available through the use of +OpenStack deployment tools, making the entire storage control and data paths +highly available. + diff --git a/Scenario_Seperate_Sections/Section_6_multi_site.rst b/Scenario_Seperate_Sections/Section_6_multi_site.rst new file mode 100644 index 0000000..2e43471 --- /dev/null +++ b/Scenario_Seperate_Sections/Section_6_multi_site.rst @@ -0,0 +1,45 @@ +6, Multisite Scenario +==================================================== + +The Multisite scenario refers to the cases when VNFs are deployed on multiple VIMs. +There could be three typical usecases for such scenario. + +One is in one DC, multiple openstack clouds are deployed. Taking into consideration that the +number of compute nodes in one openstack cloud are quite limited (nearly 100) for +both opensource and commercial product of openstack, multiple openstack clouds will +have to be deployed in the DC to manage thousands of servers. In such a DC, it should +be possible to deploy VNFs accross openstack clouds. + + +Another typical usecase is Geographic Redundancy (GR). GR deployment is to deal with more +catastrophic failures (flood, earthquake, propagating software fault, and etc.) of a single site. +In the Geographic redundancy usecase, VNFs are deployed in two sites, which are +geographically seperated and are deployed on NFVI managed by seperate VIM. When +such a catastrophic failure happens, the VNFs at the failed site can failover to +the redundant one so as to continue the service. Different VNFs may have specified +requirement of such failover. Some VNFs may need stateful failover, while others +may just need their VMs restarted on the redundant site in their initial state. +The first would create the overhead of state replication. The latter may still +have state replication through the storage. Accordingly for storage we don't want +to loose any data, and for networking the NFs should be connected the same way as +they were in the original site. We probably want also to have the same number of +VMs on the redundant site coming up for the VNFs. + + +The other usecase is the maintainance. When one site is planning for a maintaining, +it should first replicate the service to another site before it stops them. Such +replication should not disturb the service, nor should it cause any data loss. The +service at the second site should be excuted, before the first site is stopped and +began maintenance. In such case, the multisite schemes may be used. + +The multisite scenario is also captured by the Multisite project, in which specific +requirements of openstack are also proposed for different usecases. However, +the multisite project mainly focuses on the requirement of these multisite +usecases on openstack. HA requirements are not necessarily the requirement +for the approaches discussed in multisite. While the HA project tries to +capture the HA requirements in these usecases. The following links are the scenarios +and Usecases discussed in the Multisite project. +https://gerrit.opnfv.org/gerrit/#/c/2123/ +https://gerrit.opnfv.org/gerrit/#/c/1438/. + + diff --git a/Scenario_Seperate_Sections/StorageImages/FTCluster.png b/Scenario_Seperate_Sections/StorageImages/FTCluster.png Binary files differnew file mode 100644 index 0000000..c42f4a0 --- /dev/null +++ b/Scenario_Seperate_Sections/StorageImages/FTCluster.png diff --git a/Scenario_Seperate_Sections/StorageImages/HostStorageCluster.png b/Scenario_Seperate_Sections/StorageImages/HostStorageCluster.png Binary files differnew file mode 100644 index 0000000..baca591 --- /dev/null +++ b/Scenario_Seperate_Sections/StorageImages/HostStorageCluster.png diff --git a/Scenario_Seperate_Sections/StorageImages/RedundantStoragePaths.png b/Scenario_Seperate_Sections/StorageImages/RedundantStoragePaths.png Binary files differnew file mode 100644 index 0000000..1850ca9 --- /dev/null +++ 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