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diff --git a/Scenario/scenario_analysis_multi_site.rst b/Scenario/scenario_analysis_multi_site.rst new file mode 100644 index 0000000..016fe58 --- /dev/null +++ b/Scenario/scenario_analysis_multi_site.rst @@ -0,0 +1,70 @@ +5, Multisite Scenario +==================================================== + +The Multisite scenario refers to the cases when VNFs are deployed on multiple VIMs. +There could be two typical usecases for such scenario. + +One is in one DC, multiple openstack cloud are deployed. Taking 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 cloud will +have to be deployed in the DC to manage thousands of servers. VNFs in such DC should +be possible to be deployed accross openstack cloud. +..[MT] Do we anticipate HA VNFs that require more than 100 VMs so that they need to +be deployed across DCs? Or the goal is to provide higher availability by deploying +across DCs? +..[fq] Here I just try to explain what multisite scenario means. I don't think HA should +be discussed in this scenario since as you said, we can not have 100 more VMs deployed +to be HA. + +The other typical usecase is geographic redundancy. GR deployment is to deal with more +catastrophic failures (flood, earthquake, propagating software fault, and etc.) for one site. +In the Geographic redundancy usecase, VNFs are deployed in two sites, which are +geographically seperated and are 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 +proceed the service. +..[MT] I agree and this scenario is definitely not limited to HA VNFs. Thus there could +be different mechanisms for the state replication between the sites and from an HA +perspective in this case it is important that the replication mechanism does not degrade +the performance at normal behaviour. + +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. +https://gerrit.opnfv.org/gerrit/#/c/2123/ +https://gerrit.opnfv.org/gerrit/#/c/1438/. + + +An architecure of stateful VNF with redundancy in the multisite scenario can be as +follows. Architecture for the other cases can be worked out accordingly. +https://wiki.opnfv.org/_detail/stateful_vnf_in_multisite_scenario.png?id=scenario_analysis_of_high_availability_in_nfv +..[MT] What is the relation of the VMs of a single site e.g. on the left hand side? +Do they collaborate? Do they protect each other? What makes the two VIMs independent +if they need to support that VNF and its VNFM? Could they be logically the same +VIM and wouldn't that be a better solution for the VNF? +..[fq] This is kind of architecture captureed from the multisite project's work. +One VM on the left site is acting as the active VNFC, and the other VM at the right +site is acting as the standby. I assume the two VIM are cooperate with each other +under the control of the orchestrator. I am also thinking that if the two VMs contrled +by one VIM would be a better solution. But apparently that is not the scenario for +multisite, cause they are thinking multisite means you have multi openstack. + + +Below listed the additinal labor and extra requirements of multisite comparing with +the basic usecases. + +1, specific network support for the active/standby or active/active VNFs across VIM. + +In the multisite scenario, instances constructing the VNFs can be placed across VIM. +This will introduce extra network support requirement. For example, heartbeat between +active/standby VMs placed across VIM requires overlay L2 network. The IP address used +for VNF to connect with other VNFs should be able to be floating across VIM as well. + +2, in the multisite scenario, a logical instance of VNFM should be put on multiple +VIM to manage the instances of VNFs placed across the VIM. + +3, in the VM failure scenarios, recovery of failed VM requires interface between +VNFM and the VIM. In the multisite scenario, the VNFM should have knowledge of +which VIM it should communicate with so as to recover the failed VNF.
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