[ClusterLabs] design question to DRBD

Digimer lists at alteeve.ca
Wed Jun 22 10:54:13 EDT 2016

On 22/06/16 08:30 AM, 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 ?
> 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) ?
> Thanks.
> Bernd

Our approach to this problem is a 2-node cluster using DRBD to back
virtual machines, and then we make he VMs the HA service. This way, to
you and whomever works on the system, you can ignore the HA stuff and
treat it like a regular server. If anything happens to the current host,
the server reboots on the good node. Being a VM, reboots are generally
quite quick.

We've detailed how we build our system in detail here:


However, you may want to use pacemaker instead of cman+rgmanager. In
that case, the tutorial above is still useful as it explains the
approach. You can just mentally switch "cman+rgmanager" for "pacemaker",
adjust the actual commands and the rest of the guide works fine.

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