[pgpool-general: 6163] Re: Fwd: repeat the check of the trusted servers

Tue Jul 24 21:05:07 JST 2018

Hi Piotr,

The purpose of trusted_servers is to make sure the Pgpool-II node which
gets isolated from
network because of some network partitioning remove itself from the
Pgpool-II cluster.
Suppose in some hypothetical environment one wants that every Pgpool-II
node should remain
connected or can access the internet or public network, so that users from
other networks can access the service,
while at the same time watchdog use the internal private network
(delegate-ip would be public IP in this case).
So the way to verify the connectivity of Pgpool-II node with external
network or internet is to use trusted_servers config.
for example you can use 'pgpool.net' in trusted server list to ensure that
Pgpool-II node is not isolated from
internet and able to ping the public website on internet. and as soon as
the node fail to ping the pgpool.net it will
declare itself dead even if it can reach the other pgpool nodes on local
network.

trusted_servers config could be used to mitigate the split-brain syndrome
in older versions of Pgpool-II but
if you are on 3.6.7 which has the quorum aware watchdog system you don't
require to use trusted_servers config
and leave it empty, of course if you don't have some other specific
requirements as the one I described in above example.

Please let me know if you need further clarification or explanation.

Thanks
Best Regards
Muhammad Usama

On Mon, Jul 23, 2018 at 7:55 PM Piotr Gbyliczek <P.Gbyliczek at node4.co.uk>
wrote:

> Hi,
>
> Sorry for reviving old thread, but I've recently gone up to 3.6.7 and
> observed
> same behavior.
>
> As I understand it, trusted_servers is a mechanism that should prevent
> standby
> pgpool service to bring up the delegated IP, and cause split brain where
> there
> is a network partition between pgpool servers.
>

> But struggling to see why standby that is able to communicate with it's
> master
> over watchdog channel would declare itself dead upon failing to contact
> trusted_servers.
>
> In fact I've had two scenarios :
> - standby pgpool declared itself dead on failing to contact trusted
> server,
> which was discovered when master pgpool was manually stopped and there was
> no
> standby to fall back to.
> - master declared itself dead on failing to contact trusted server, which
> initiated failover procedure and standby picked up the master role,
> bringing
> up the delegated IP. this is correct behavior in general, but have been
> noticed by customers and monitoring, hence some question have been raised.
>
> I would say both could be avoided, and were unnecessary downtime for the
> delegated IP.
>
> Was there any conclusion to this issue, or design explanation to the
> behavior
> ?
>
> Thanks,
> Piotr
> --
>
>
>   Piotr Gbyliczek
> ------------------------------
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