Change to 18 initiative to ensure we can allow a partner to use replication for DR solutions

Feature Overview

Adding support for Cinder's async replication for rbd backend, the feature is already implemented in upstream but was never supported in RHOSP. Replication provides a Disaster reovery (DR) solution for mission-critical workloads. It has two parts, Cinder side and driver side. This feature only focus on Cinder replication with rbd driver. 

https://docs.openstack.org/cinder/latest/contributor/replication.html

Goals

• The Cinder replication will help customer to have failover and failback across two Ceph clusters in case of failure of primary Ceph cluster. 
• This feature can also serve as building block for building DR solutions to copy volume data across two backends.
• Validate the existing feature in upstream and downstream CI.
• Add the missing automation tests to verify failover and failback.

Requirements (mandatory -_ Complete while in Refinement status):
A list of specific needs, capabilities, or objectives that a Feature must deliver to satisfy the Feature. Some requirements will be flagged as MVP. If an MVP gets shifted, the Feature shifts. If a non MVP requirement slips, it does not shift the feature.

Done - Acceptance Criteria

1. No regression in case of failover and failback
2. Add test coverage for failover and failback
3. Data should remain intact after failover and failback
4. Ability to enable and configure the replication at the time of deployment.
5. Clear list of supported and unsupported scenarios for rbd replication.
6. Upstream and downstream CI coverage for this feature.
7. Full downstream documentation covering enablement, configuration and procedure to failover and failback.

Use Cases - i.e. User Experience & Workflow: (Initial completion while in Refinement status):
Include use case diagrams, main success scenarios, alternative flow scenarios.
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Out of Scope

• Synchronous replication
• Other backends, individual vendors will certify and support their own replication drivers.

Documentation Considerations 

• Procedure to enable and configure replication
• Prrequisites like rbd-mirriong and other ceph configuration.
• Procedure for failover
• Procedure for failback
• List of operations supported/unsupported after failover

Questions to Answer

Background and Strategic Fit 

Customer Considerations

Team Sign Off (Completion while in Planning status)

• All required Epics (known at the time) are linked to the this Feature
• All required Stories, Tasks (known at the time) for the most immediate Epics have been created and estimated
• Add - Reviewers name, Team Name
• Acceptance == Feature as “Ready” - well understood and scope is clear - Acceptance Criteria (scope) is elaborated, well defined, and understood
• Note: Only set FixVersion/s: on a Feature if the delivery team agrees they have the capacity and have committed that capability for that milestone

• …

Questions 

• What is our ideal downstream test case for the DR use case and does it need to be 2 clusters?
• Review current approach 
• Is just replication v1 required (no changes to current functionality)
  • YES