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diff --git a/Scenario_1/scenario_analysis_VNF_external_interface.rst b/Scenario_1/scenario_analysis_VNF_external_interface.rst new file mode 100644 index 0000000..c634c20 --- /dev/null +++ b/Scenario_1/scenario_analysis_VNF_external_interface.rst @@ -0,0 +1,99 @@ +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 Interfacece + +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. + +..[MT] In general I would rather say that the IP address is managed by the HA +manager and not provided. But as a concrete use case "provide" works fine. +So it depends how you want to use this text. +..[fq] Agree, Thank you! + +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 recover the failed one, and should also exclude the +failed VNFC from the cluster so that the LB will re-route the traffic to +to the other VNFCs. 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. + +..[MT] I think this use case needs to show also how the LB learns about the new VNFC. +Also we should distinguish VNFC and VM failures as VNFC failure wouldn't be detected +in the NFVI e.g. LB, so we need a resolution, an applicability comment at least. +..[fq] I think I have made a mistake here by saying the VNFC. Actually if the failure +only happens in VNFC, the VNFC should reboot itself rather than have a new VNFC taking +its place. So in this case, I think I should modify VNFC into VMs. And as you mentioned, +the NFVI level can hardly detect VNFC level failure. + +..[MT] There could also be a combined case for the N+M redundancy, when there are N +actives but also M standbys at the VNF level. +..[fq] It could be. But I actually haven't see such a deployed case. So I am not sure +if I can discribe the schemes correctly:) + +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, + +..[MT] I don't understand the yellow inserted text +..[fq] Neither do I, actually. I think it is added by some one else and I can't make +out what it means as well:) + +- it could be through a shared storage assigned to the whole VNF + +- through in-memory database (checkpointing), when the database (checkpoint service) takes care of the data replication. |