BDR/HAProxy server pool management v23

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The tpaexec pool-disable-server and pool-enable-server commands allow a PGD instance in a BDR-Always-ON cluster to be temporarily removed from the HAProxy active server pool for maintenance, and then added back afterwards.

These commands follow the same process as rolling updates by default, so pool-disable-server will wait for active transactions against a PGD instance to complete and for pgbouncer to direct new connections to another instance before completing. Use the --nowait option if you don't want to wait for active sessions to end.

Running pool-disable-server immediately followed by pool-enable-server on an instance will have the effect of moving all active traffic to a different instance (in essence, a switchover). This allows you to run online maintenace tasks such as long-running VACUUM commands, while maintaining instance availability.

If there are multiple HAProxy servers configured with the same set of haproxy_backend_servers, this command will remove or add the given server to the pool of every relevant proxy in parallel.

Example

$ tpaexec pool-disable-server ~/clusters/clockwork orange # --nowait

# HAProxy will no longer direct any traffic to the PGD instance named
# 'orange', so you can perform maintenance on it (e.g., run `tpaexec
# rehydrate`).

$ tpaexec pool-enable-server ~/clusters/clockwork orange

When you remove an instance from the server pool, HAProxy will not direct any traffic to it, even if the other instance(s) in the pool fail. You must remember to add the server back to the active pool once the maintenance activity is concluded.