vRealize Automation 7.3 Postgres Database Automatic Failover Scenarios


vRealize Automation 7.3 Postgres Database Automatic Failover Scenarios


when three appliances are deployed, and synchronous replication is configured for them in vRA 7.3, PostgreSQL database failover is automatic works.
if there is a problem with the vRealize Automation appliance Postgres database in vRA7.2.  you need to do manually fail over to a replica vRealize Automation appliance node in the cluster.
vRealize Automation uses the PostgreSQL master-replica model to support data replication. This means that all the database nodes work in a cluster with one leading node, known as the master, and several replicating nodes, known as replicas. The master node handles all database requests and the replica nodes stream and replay transactions from the master locally.

Three Node ( vRA 7.3 ) Auto Failover Scenarios

Scenario 1: Single Node Failure Scenarios

A- Master Node Fails
Normal Behavior
•The configured sync replica node becomes the master and automatically picks up appliance database functionality.
•The potential sync replica becomes the sync standby node.
•The vRealize Automation deployment functions in read only mode until the automatic failover completes.
Next Step
•When the former master is recovered, it will be reset as replica automatically by the failover agent repair logic. No manual action is required.
•If the former master cannot be recovered, manually set the appliance database to asynchronous mode.

B-The Sync Replica Fails
Normal Behavior
•The vRealize Automation deployment experiences no downtime. There will be a delay of a couple of seconds for database requests until the potential replica becomes the new sync replica. The appliance database performs this action automatically.
Next Step
•When the former synch replica comes online, it will become a potential replica automatically. No manual action is required.
•If the former sync replica cannot be repaired, manually set the appliance database to asynchronous mode.

C-Potential Replica Fails
Normal Behavior
No deployment downtime.
Next Step
•When the former potential replica comes online, it becomes a potential replica automatically. No manual action is required.
•If the former potential replica cannot be repaired, set the appliance database to asynchronous mode.

Scenario 2- Two Node Failure Scenarios
If two out of the three nodes fail same time, vRealize Automation switches to read only mode until a manual repair is performed.
A- Master Node and Potential Replica Fail
Normal Behavior
•The sync replica is not promoted to master automatically. vRealize Automation will switch to read only mode until a manual promotion is performed.
Next Step
•Manual action is required. Set the appliance database to asynchronous mode.
•When the master and potential replica are recovered, manually set them to synchronize against the new master. At that point, you can switch vRealize Automation back to synchronous mode.
•When two out of three nodes are down at the same time, vRealize Automation will switch to read-only mode until you effect a manual repair. If only one database node is available, switch your deployment to asynchronous mode.

B-  Sync and Potential Replicas Fail

Normal Behavior
•The master is unable to process read/write transactions. vRealize Automation functions in read only mode until a manual repair is performed.

Next Step
•Manual promotion is required. Set the appliance database to asynchronous mode.
•When the sync and potential replicas are recovered, they should be manually reset to synchronize against the master. At this point, you can switch vRealize Automation back to synchronous mode.
•When two out of three nodes are down simultaneously, vRealize Automation will switch to read-only mode until you effect a manual repair. If only one database node is available, switch your deployment to asynchronous mode.



Scenario 3 - Link failure happens between NODES

If a link failure occurs among nodes on a distributed deployment, the automatic failover agent attempts to repair the configuration.

A-Link Failure between SITE A and SITE B, but all 3 nodes are UP and ONLINE
Site A: Master and potential replica
Site B: Sync replica
Normal Behavior
•No downtime for the vRealize Automation deployment. The potential replica automatically becomes the sync replica
Next Step
•No manual action is required.

B-Link Failure between SITE A and SITE B, but all 3 nodes are UP and ONLINE
Site A: Master
Site B: Sync and potential replica

Normal Behavior
•Sync replica becomes the master and automatically picks up appliance database functionality. Automatic failover agent promotes the potential replica to become the new sync replica. vRealize Automation deployment operates in read only mode until this promotion completes.

Next Step
•No manual action is required. When the link is recovered, the automatic failover agent resets the former master as replica.


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