[pgpool-general: 2864] Re: How to deploy pgpool with no single point of failure and without virtual IP address failover?

[Juergen Brendel]

Hello!

Thank you for your reply.


On Wed, 2014-05-21 at 06:28 +0900, Tatsuo Ishii wrote:
> > As far as I understand, this problem can normally be solved by having
> > pgpool-HA with virtual IP address failover, so that (as far as the app
> > servers are concerned) there really only is one pgpool instance and only
> > one pgpool instance at any time will really be used. However, I'm in a
> > hosted VPC environment (something like EC2 or DigitalOcean) and I can't
> > just quickly failover any IP addresses.
> 
> I don't understand this. You could have two pgpool-II instances at a
> same time if you enable "watchdog" functionality of pgpool-II. What
> kind of problems do yo see in this configuration?

Ok, so maybe my understanding of the 'watchdog' in pgpool is not
sufficient. I've looked here:

http://www.pgpool.net/docs/pgpool-II-3.2.0/tutorial-watchdog-en.html

It looks like the use of a virtual IP address is somehow implied.
However, that won't be possible for me. So, are you saying that
pgpool-watchdog is useful even if no virtual IP addresses are used?

Will it be possible to have multiple pgpool instances active (and used
by different clients) at the same time? And that the watchdog mechanism
can be used to synchronize the pgpool-instances' picture of who is
currently DB master and who is slave?

Juergen