High level architecture and general features ============================================ Functional overview ------------------- The Doctor project circles around two distinct use cases: 1) management of failures of virtualized resources and 2) planned maintenance, e.g. migration, of virtualized resources. Both of them may affect a VNF/application and the network service it provides, but there is a difference in frequency and how they can be handled. Failures are spontaneous events that may or may not have an impact on the virtual resources. The Consumer should as soon as possible react to the failure, e.g., by switching to the STBY node. The Consumer will then instruct the VIM on how to clean up or repair the lost virtual resources, i.e. restore the VM, VLAN or virtualized storage. How much the applications are affected varies. Applications with built-in HA support might experience a short decrease in retainability (e.g. an ongoing session might be lost) while keeping availability (establishment or re-establishment of sessions are not affected), whereas the impact on applications without built-in HA may be more serious. How much the network service is impacted depends on how the service is implemented. With sufficient network redundancy the service may be unaffected even when a specific resource fails. On the other hand, planned maintenance impacting virtualized resources are events that are known in advance. This group includes e.g. migration due to software upgrades of OS and hypervisor on a compute host. Some of these might have been requested by the application or its management solution, but there is also a need for coordination on the actual operations on the virtual resources. There may be an impact on the applications and the service, but since they are not spontaneous events there is room for planning and coordination between the application management organization and the infrastructure management organization, including performing whatever actions that would be required to minimize the problems. Failure prediction is the process of pro-actively identifying situations that may lead to a failure in the future unless acted on by means of maintenance activities. From applications' point of view, failure prediction may impact them in two ways: either the warning time is so short that the application or its management solution does not have time to react, in which case it is equal to the failure scenario, or there is sufficient time to avoid the consequences by means of maintenance activities, in which case it is similar to planned maintenance. Architecture Overview --------------------- NFV and the Cloud platform provide virtual resources and related control functionality to users and administrators. :num:`Figure #figure3` shows the high level architecture of NFV focusing on the NFVI, i.e., the virtualized infrastructure. The NFVI provides virtual resources, such as virtual machines (VM) and virtual networks. Those virtual resources are used to run applications, i.e. VNFs, which could be components of a network service which is managed by the consumer of the NFVI. The VIM provides functionalities of controlling and viewing virtual resources on hardware (physical) resources to the consumers, i.e., users and administrators. OpenStack is a prominent candidate for this VIM. The administrator may also directly control the NFVI without using the VIM. Although OpenStack is the target upstream project where the new functional elements (Controller, Notifier, Monitor, and Inspector) are expected to be implemented, a particular implementation method is not assumed. Some of these elements may sit outside of OpenStack and offer a northbound interface to OpenStack. General Features and Requirements --------------------------------- The following features are required for the VIM to achieve high availability of applications (e.g., MME, S/P-GW) and the Network Services: * Monitoring: Monitor physical and virtual resources. * Detection: Detect unavailability of physical resources. * Correlation and Cognition: Correlate faults and identify affected virtual resources. * Notification: Notify unavailable virtual resources to their Consumer(s). * Recovery action: Execute actions to process fault recovery and maintenance. The time interval between the instant that an event is detected by the monitoring system and the Consumer notification of unavailable resources shall be < 1 second (e.g., Step 1 to Step 4 in :num:`Figure #figure4` and :num:`Figure #figure5`). .. _figure3: .. figure:: images/figure3.png :width: 100% High level architecture Monitoring ^^^^^^^^^^ The VIM shall monitor physical and virtual resources for unavailability and suspicious behavior. Detection ^^^^^^^^^ The VIM shall detect unavailability and failures of physical resources that might cause errors/faults in virtual resources running on top of them. Unavailability of physical resource is detected by various monitoring and managing tools for hardware and software components. This may include also predicting upcoming faults. Note, fault prediction is out of scope of this project and is investigated in the OPNFV "Data Collection for Failure Prediction" project [PRED]_. The fault items/events to be detected shall be configurable. The configuration shall enable Failure Selection and Aggregation. Failure aggregation means the VIM determines unavailability of physical resource from more than two non-critical failures related to the same resource. There are two types of unavailability - immediate and future: * Immediate unavailability can be detected by setting traps of raw failures on hardware monitoring tools. * Future unavailability can be found by receiving maintenance instructions issued by the administrator of the NFVI or by failure prediction mechanisms. Correlation and Cognition ^^^^^^^^^^^^^^^^^^^^^^^^^ The VIM shall correlate each fault to the impacted virtual resource, i.e., the VIM shall identify unavailability of virtualized resources that are or will be affected by failures on the physical resources under them. Unavailability of a virtualized resource is determined by referring to the mapping of physical and virtualized resources. The relation from physical resources to virtualized resources shall be configurable, as the cause of unavailability of virtualized resources can be different in technologies and policies of deployment. Failure aggregation is also required in this feature, e.g., a user may request to be only notified if failures on more than two standby VMs in an (N+M) deployment model occurred. Notification ^^^^^^^^^^^^ The VIM shall notify the alarm, i.e., unavailability of virtual resource(s), to the Consumer owning it over the northbound interface, such that the Consumers impacted by the failure can take appropriate actions to recover from the failure. The VIM shall also notify the unavailability of physical resources to its Administrator. All notifications shall be transferred immediately in order to minimize the stalling time of the network service and to avoid over assignment caused by delay of capability updates. There may be multiple consumers, so the VIM has to find out the owner of a faulty resource. Moreover, there may be a large number of virtual and physical resources in a real deployment, so polling the state of all resources to the VIM would lead to heavy signaling traffic. Thus, a publication/subscription messaging model is better suited for these notifications, as notifications are only sent to subscribed consumers. Note: the VIM should only accept individual notification URLs for each resource by its owner or administrator. Notifications to the Consumer about the unavailability of virtualized resources will include a description of the fault, preferably with sufficient abstraction rather than detailed physical fault information. Flexibility in notifications is important. For example, the receiver function in the consumer-side implementation could have different schema, location, and policies (e.g. receive or not, aggregate events with the same cause, etc.). Recovery Action ^^^^^^^^^^^^^^^ In the basic "Fault management using ACT-STBY configuration" use case, no automatic actions will be taken by the VIM, but all recovery actions executed by the VIM and the NFVI will be instructed and coordinated by the Consumer. In a more advanced use case, the VIM shall be able to recover the failed virtual resources according to a pre-defined behavior for that resource. In principle this means that the owner of the resource (i.e., its consumer or administrator) can define which recovery actions shall be taken by the VIM. Examples are a restart of the VM, migration/evacuation of the VM, or no action. High level northbound interface specification --------------------------------------------- Fault management ^^^^^^^^^^^^^^^^ This interface allows the Consumer to subscribe to fault notification from the VIM. Using a filter, the Consumer can narrow down which faults should be notified. A fault notification may trigger the Consumer to switch from ACT to STBY configuration and initiate fault recovery actions. A fault query request/response message exchange allows the Consumer to find out about active alarms at the VIM. A filter can be used to narrow down the alarms returned in the response message. .. _figure4: .. figure:: images/figure4.png :width: 100% High-level message flow for fault management The high level message flow for the fault management use case is shown in :num:`Figure #figure4`. It consists of the following steps: 1. The VIM monitors the physical and virtual resources and the fault management workflow is triggered by a monitored fault event. 2. Event correlation, fault detection and aggregation in VIM. Note: this may also happen after Step 3. 3. Database lookup to find the virtual resources affected by the detected fault. 4. Fault notification to Consumer. 5. The Consumer switches to standby configuration (STBY) 6. Instructions to VIM requesting certain actions to be performed on the affected resources, for example migrate/update/terminate specific resource(s). After reception of such instructions, the VIM is executing the requested action, e.g., it will migrate or terminate a virtual resource. NFVI Maintenance ^^^^^^^^^^^^^^^^ The NFVI maintenance interface allows the Administrator to notify the VIM about a planned maintenance operation on the NFVI. A maintenance operation may for example be an update of the server firmware or the hypervisor. The MaintenanceRequest message contains instructions to change the state of the resource from 'normal' to 'maintenance'. After receiving the MaintenanceRequest, the VIM will notify the Consumer about the planned maintenance operation, whereupon the Consumer will switch to standby (STBY) configuration to allow the maintenance action to be executed. After the request was executed successfully (i.e., the physical resources have been emptied) or the operation resulted in an error state, the VIM sends a MaintenanceResponse message back to the Administrator. .. _figure5: .. figure:: images/figure5.png :width: 100% High-level message flow for NFVI maintenance The high level message flow for the NFVI maintenance use case is shown in :num:`Figure #figure5`. It consists of the following steps: 1. Maintenance trigger received from administrator. 2. VIM switches the affected NFVI resources to "maintenance" state, i.e., the NFVI resources are prepared for the maintenance operation. For example, the virtual resources should not be used for further allocation/migration requests and the VIM will coordinate with the Consumer on how to best empty the physical resources. 3. Database lookup to find the virtual resources affected by the detected maintenance operation. 4. StateChange notification to inform Consumer about planned maintenance operation. 5. The Consumer switches to standby configuration (STBY) 6. Instructions from Consumer to VIM requesting certain actions to be performed (step 6a). After receiving such instructions, the VIM executes the requested action in order to empty the physical resources (step 6b) and informs the Consumer is about the result of the actions. Note: this step is out of scope of Doctor. 7. Maintenance response from VIM to inform the Administrator that the physical machines have been emptied (or the operation resulted in an error state). 8. The Administrator is coordinating and executing the maintenance operation/work on the NFVI. Note: this step is out of scope of Doctor. Faults ------ Faults in the listed elements need to be immediately notified to the Consumer in order to perform an immediate action like live migration or switch to a hot standby entity. In addition, the Administrator of the host should trigger a maintenance action to, e.g., reboot the server or replace a defective hardware element. Faults can be of different severity, i.e., critical, warning, or info. Critical faults require immediate action as a severe degradation of the system has happened or is expected. Warnings indicate that the system performance is going down: related actions include closer (e.g. more frequent) monitoring of that part of the system or preparation for a cold migration to a backup VM. Info messages do not require any action. We also consider a type "maintenance", which is no real fault, but may trigger maintenance actions like a re-boot of the server or replacement of a faulty, but redundant HW. Faults can be gathered by, e.g., enabling SNMP and installing some open source tools to catch and poll SNMP. When using for example Zabbix one can also put an agent running on the hosts to catch any other fault. In any case of failure, the Administrator should be notified. Table 1 provides a list of high level faults that are considered within the scope of the Doctor project requiring immediate action by the Consumer. +------------------+---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | Service | Fault | Severity | How to detect? | Comment | Action to recover | +------------------+---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | Compute Hardware | Processor/CPU failure, CPU condition not ok | Critical | Zabbix | | Switch to hot standby | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | Memory failure/Memory condition not ok | Critical | Zabbix (IPMI) | | Switch to hot standby | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | Network card failure, e.g. network adapter connectivity lost | Critical | Zabbix/Ceilometer | | Switch to hot standby | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | Disk crash | Info | RAID monitoring | Network storage is very redundant (e.g. RAID system) and can guarantee high availability | Inform OAM | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | Storage controller | Critical | Zabbix (IPMI) | | Live migration if storage is still accessible; otherwise hot standby | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | PDU/power failure, power off, server reset | Critical | Zabbix/Ceilometer | | Switch to hot standby | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | Power degradation, power redundancy lost, power threshold exceeded | Warning | SNMP | | Live migration | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | Chassis problem (.e.g fan degraded/failed, chassis power degraded), CPU fan problem, temperature/thermal condition not ok | Warning | SNMP | | Live migration | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | Mainboard failure | Critical | Zabbix (IPMI) | | Switch to hot standby | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | OS crash (e.g. kernel panic) | Critical | Zabbix | | Switch to hot standby | +------------------+---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | Hypervisor | System has restarted | Critical | Zabbix | | Switch to hot standby | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | Hypervisor failure | Warning/Critical | Zabbix/Ceilometer | | Evacuation/switch to hot standby | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | Zabbix/Ceilometer is unreachable | Warning | ? | | Live migration | +------------------+---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | Network | SDN/OpenFlow switch, controller degraded/failed | Critical | ? | | Switch to hot standby or reconfigure virtual network topology | + +---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ | | Hardware failure of physical switch/router | Warning | SNMP | Redundancy of physical infrastructure is reduced or no longer available | Live migration if possible, otherwise evacuation | +------------------+---------------------------------------------------------------------------------------------------------------------------+------------------+-------------------+------------------------------------------------------------------------------------------+----------------------------------------------------------------------+ .. vim: set tabstop=4 expandtab textwidth=80: