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diff --git a/Scenario_2/scenario_analysis_multi_site.rst b/Scenario_2/scenario_analysis_multi_site.rst new file mode 100644 index 0000000..b9df8d0 --- /dev/null +++ b/Scenario_2/scenario_analysis_multi_site.rst @@ -0,0 +1,51 @@ +5, 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. +..(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. + +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. +..(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 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. 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. +https://gerrit.opnfv.org/gerrit/#/c/2123/ +https://gerrit.opnfv.org/gerrit/#/c/1438/. + + |