What he said, and you also may want to look at pgpool-II. I’ve had fairly good luck with that and Tatsuo (the author) hangs out here occasionally too. — Jay Sent from my iPad > On Jan 5, 2018, at 4:00 PM, Jehan-Guillaume (ioguix) de Rorthais <ioguix@xxxxxxx> wrote: > > On Fri, 5 Jan 2018 13:07:10 -0600 > Azimuddin Mohammed <azimeiu@xxxxxxxxx> wrote: > >> Hello, >> I am little confused with how HA works in postgres. Reading the article >> which state as below "*If the primary server fails and the standby server >> becomes the new primary, and then the old primary restarts, you must have a >> mechanism for informing the old primary that it is no longer the primary. >> This is sometimes known as STONITH (Shoot The Other Node In The Head), >> which is necessary to avoid situations where both systems think they are >> the primary, which will lead to confusion and ultimately data loss.* >> >> *Many failover systems use just two systems, the primary and the standby, >> connected by some kind of heartbeat mechanism to continually verify the >> connectivity between the two and the viability of the primary. It is also >> possible to use a third system (called a witness server) to prevent some >> cases of inappropriate failover, but the additional complexity might not be >> worthwhile unless it is set up with sufficient care and rigorous testing.* >> *PostgreSQL does not provide the system software required to identify a >> failure on the primary and notify the standby database server. Many such >> tools exist and are well integrated with the operating system facilities >> required for successful failover, such as IP address migration."* >> >> Can someone explain how the HA failback will take place > > The failback need either to rebuild the old master as a standby (rsync, > pg_basebackup, restore PITR, ...) or to use pg_rewind to rewind the old master > to a point where it can catch up with the new master. > > Some tools tries to automate failback using pg_rewind (patroni, repmgr), but I > have no experience with them. > >> and what open source tools we can use to make sure once the primary server >> which failed over to slave will mark itself as slave. > > There's a lot of open source tools to build some HA around PgSQL: Repmgr, > Patroni (based on etcd or zookeeper), PAF (based on Pacemaker), etc. You will > have to spend a lot of time to make extensive tests, understand them, pick one > and document your cluster. > > Regards, >
