Postgres HA

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 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.

Appreciate your response in advance.

--

Regards,
Azim

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