On Wed, Jan 08, 2020 at 11:06:28PM -0500, Rita wrote: > I run a master and standby setup with Postgresql 11. The systems are > identical from a hardware and software setup. If the master goes down I > can do a pg_ctl promote on the standby and point my applications to use the > standby (new master). > > Once the original master is online, when is an appropriate time to fail > back over? And are there any other things besides promote after the > failover is done? Make sure that you still have an HA configuration able to handle multiple degrees of failures with always standbys available after a promotion. The options available to rebuild your HA configuration after a failover depend on the version of PostgreSQL you are using. After a failover the most simple solution would be to always recreate a new standby from a base backup taken from the freshly-promoted primary, though it can be costly depending on your instance. You could also use pg_rewind (available in core since 9.5) to recycle the previous primary and reuse it as a standby of the new promoted custer. Note that there are community-based solutions for such things, like pg_auto_failover or pacemaker-based stuff just to name two. These rely on more complex architectures, where a third node is present to monitor the others (any sane HA infra ought to do at least that to be honest). -- Michael
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