[ClusterLabs] design question to DRBD

[Klaus Wenninger]

On 06/22/2016 02:30 PM, Lentes, Bernd wrote:
> Hi,
>
> we have a two node cluster. It is running a Web-Application. Web-Application needs a MySQL Database, has static and dynamic (perlscripts) webpages.
> I will make the DB HA with MySQL replication.
> From time to time it's likely that something in the webapp is changed, so we have to edit some scripts or install a perl module.
> I would like have the changes automatically synchronized to the other side, without any manual intervention. And also without knowing which node is the active one.
> I'm thinking about putting /srv/www and /usr/lib/perl5 on a DRBD device in an active/active webapp. For that i need a cluster FS and DLM, right ?
> This should synchronize automatically in both directions ?
How are you applying your updates?
Especially under /usr/lib/perl5 the packet-management should be used.
That said you would confuse your packet-management when the files change
without the local database being updated.
> Do the services have to a ressource for this setup of DRBD or is it possible to have them as "normal" services, started by init.
> Or is it better to have them as ressources because other services will also run in this HA-system (likely some virtual machines) ?
If you are having the mentioned subtrees on DRBD mounting a filesystem,
after the drbd-device is up, will be involved and
doing that is probably not a good idea while the subtree is actively used.
So I would opt for having everything that is using the subtree under HA
control.

regards,
Klaus
>
> Thanks.
>
>
> Bernd
>