[Pacemaker] Quorum in pacemaker

[Vijay B]

Hi Andrew,

Thanks for the responses! I set the cman quorum timeout to 0, and the first
node came up.

However, I'm seeing newer issues now that I hadn't seen before, when
creating a resource of an LSB compliant service. I will send another mail
to the ML to keep that discussion separate.

Regards,
Vijay


On Thu, Jun 26, 2014 at 5:45 PM, Andrew Beekhof <andrew at beekhof.net> wrote:

>
> On 27 Jun 2014, at 10:22 am, Vijay B <os.vbvs at gmail.com> wrote:
>
> > Hi,
> >
> > I'm trying to set up a three node cluster using pacemaker+corosync, and
> I installed the required packages on each node, checked for their network
> connectivity so they can see each other, added the required startup scripts
> and edited the cluster.conf file as well so it includes all three nodes.
> >
> > Now, when on the first node, I attempt to start up cman using service
> cman start, it times out thus:
> >
> > vagrant at precise64-pmk1:~$ sudo service cman start
> > Starting cluster:
> >    Checking if cluster has been disabled at boot... [  OK  ]
> >    Checking Network Manager... [  OK  ]
> >    Global setup... [  OK  ]
> >    Loading kernel modules... [  OK  ]
> >    Mounting configfs... [  OK  ]
> >    Starting cman... [  OK  ]
> >    Waiting for quorum... Timed-out waiting for cluster
> > [FAILED]
> > vagrant at precise64-pmk1:~$
> >
> > Why is this? Is it because I have three nodes to begin with in my
> /etc/cluster/cluster.conf, and so this node expects that the cluster quorum
> is 2, and so it should be able to talk to at least one other node?
>
> Yes. CMAN refuses to start unless it can see enough other nodes to form
> quorum.
> Pacemaker doesn't need quorum to behave sanely though, so try:
>
> echo "CMAN_QUORUM_TIMEOUT=0" >> /etc/sysconfig/cman
>
> > At this point, I haven't started the cman or pacemaker services on the
> other nodes.
> >
> > If this is the case, what will happen when two nodes of the three die?
>
> Unrelated. This only affects startup.
> What happens in this case depends on how you configured no-quorum-policy.
>
> > In case cluster.conf changes accordingly to reflect the new cluster
> membership, what if all three nodes are simply powered off and one
> rebooted? The cluster will be down, won't it?
> >
> > What is the best way to get around this? I don't want to set
> CMAN_QUORUM_TIMEOUT=0, since as I understand it, the node would then go
> ahead and start itself as a cluster without waiting for the other nodes,
> and if this causes my service to start up
>
> Pacemaker won't start things without quorum - unless you specifically tell
> it to.
>
> > and it is already started/running on another node, it could cause issues.
> >
> > Now, I don't know how to configure quorum disks for pacemaker - is it
> possible to do this with pacemaker?
>
> Pacemaker doesn't care. Thats a cman/quorum detail.  Pacemaker only cares
> "do we have quorum".
>
> > How does it work? What are the recommended ways to address the above
> problem? I infer that if this disk is configured, the node that grabs the
> disk first becomes the president of the pacemaker cluster. In this context,
> I have another question - does corosync have its own cluster membership
> state distributed across all cluster nodes? If so, I guess quorum is
> configured at the corosync level rather than at the pacemaker level?
> >
> > Apologies in advance if my queries above are addressed in the
> documentation already - I felt it would be quicker and more accurate to ask
> the community for reliable info.
> >
> > Thanks!
> > Regards,
> > Vijay
> >
> >
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