On Fri, Jan 5, 2018 at 12:07 PM, Azimuddin Mohammed <azimeiu@gmail.com> wrote:
>
> Hello,
> I am little confused with how HA works in postgres. Reading the article which state as below "If the primary server
failsand the standby server becomes the new primary, and then the old primary restarts, you must have a mechanism for
informingthe old primary that it is no longer the primary. This is sometimes known as STONITH (Shoot The Other Node In
TheHead), which is necessary to avoid situations where both systems think they are the primary, which will lead to
confusionand ultimately data loss.
>
> Many failover systems use just two systems, the primary and the standby, connected by some kind of heartbeat
mechanismto continually verify the connectivity between the two and the viability of the primary. It is also possible
touse a third system (called a witness server) to prevent some cases of inappropriate failover, but the additional
complexitymight 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
databaseserver. Many such tools exist and are well integrated with the operating system facilities required for
successfulfailover, 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
primaryserver which failed over to slave will mark itself as slave.
>
There are LOTS of ways to implement HA.
Here's a book on the subject that's 537 pages long, and is only $4.99 right now:
https://www.packtpub.com/big-data-and-business-intelligence/postgresql-high-availability-cookbook-second-edition
I've been reading it a bit, seems to be a good resource.
--
To understand recursion, one must first understand recursion.