[Pacemaker] RHEL/CentOS 6.4: corosync -> CMAN migration

[Stefan Förster]

Hello Andrew,

* Andrew Beekhof <andrew at beekhof.net>:
> On Sun, Mar 10, 2013 at 8:35 PM, Stefan Förster
> > 1. In step (2), will pacemaker stop resources when it's brought down,
> >    despite being in maintenance mode?
> 
> No.
> _However_, you will want to stop any cluster filesystems as they're
> going die anyway.
> Both OCFS2 and GFS2 require the dlm which requires corosync/cman.
> Without those running, the filesystems can't function and will panic.

Since we don't use anything that needs global locking we will be fine.

> > 2. In step (5), will the pacemaker resource configuration be
> >    preserved throughout this migration?
> 
> Absolutely.  The only thing that changes is corosync.conf
> All the resource related configuration stays in cib.xml and is unchanged.

This is something I totally forgot - I should probably take not only
backups of "crm configure show" and the cluster's XML config
("cibadmin -Q" or something like that, I alway forget), but also
backup cib.xml - thanks for reminding me.

If anyone else has to migrate from the corosync plugin to CMAN on
RHEL/CentOS 6.4: According to the extensive testing I performed this
week, it's basically very painfree. The important things to remember,
IMHO:

1. Migrate _all_ of your corosync networking configuration, i.e:
    - secondary communication rings, DLM protocol SCTP, if used
    - port and multicast address settings (_especially_ if your
      network guys are good and give higher priority to your cluster
      communication)
    - encryption key
    - stuff that I forgot and that will bite me
2. Check startup configuration of "cman" _and_ "pacemaker". Some
   people like to start their clusters at reboot, in this case, both
   services need to be enabled using "chkconfig" (I don't really
   recommend this, but whatever).
3. Make sure to redirect CMAN fencing to pacemaker!
4. If you had non-default vote settings, migrate them!
5. If you onle have two nodes, set two_node="1" and
   expected_votes="1".
6. Migrate the logging section.

Thanks for your input on this, guys.


Cheers
Stefan