[ClusterLabs] design question to DRBD

Lentes, Bernd bernd.lentes at helmholtz-muenchen.de
Wed Jun 22 12:28:09 EDT 2016

----- On Jun 22, 2016, at 3:59 PM, Klaus Wenninger kwenning at redhat.com wrote:

> 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.

Hi Klaus,

yes, that's a good hint. I will not synchronize /usr/lib/perl with DRBD.
But for /srv/www it should be fine ?

>> 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.

And that's a more consistent setup.



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