[pgpool-general: 2865] Re: How to deploy pgpool with no single point of failure and without virtual IP address failover?

[Tatsuo Ishii]

> 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?

Sorry for confusion. The tutorial is for the case virtual IP is
mandate.  You can safely make "delegate_IP" empty (thus no virtual IP
address is given) for such a configuration you want.

> 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?

Yes you can. Each pgpool instance synchronize each other through a
communication path provided by watchdog.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp