[ClusterLabs] Minimum configuration for dynamically adding a node to a cluster

[Nikhil Utane]

Thank you for all the information.

Yes, I am using multicast. Actually i had tried without nodelist but was
hasty in reading the error message.
Saw the "'corosync_quorum' failed to load for reason configuration error:
nodelist " and didn't read the second part properly about expected_votes.
My bad.

I don't want to configure quorum since keeping the service up is of utmost
importance and the split-brain problem is indirectly getting handled
through other means.
In this case, should I be configuring expected_votes as 1?

Currently my two-nodes in the cluster discovered each other without any
nodelist and expected_votes as 1. Which is what I always wanted.

-Thanks
Nikhil

On Wed, Jun 8, 2016 at 9:53 PM, Ferenc Wágner <wferi at niif.hu> wrote:

> Nikhil Utane <nikhil.subscribed at gmail.com> writes:
>
> > Would like to know the best and easiest way to add a new node to an
> already
> > running cluster.
> >
> > Our limitation:
> > 1) pcsd cannot be used since (as per my understanding) it communicates
> over
> > ssh which is prevented.
> > 2) No manual editing of corosync.conf
>
> If you use IPv4 multicast for Corosync 2 communication, then you needn't
> have a nodelist in corosync.conf.  However, if you want a quorum
> provider, then expected_votes must be set correctly, otherwise a small
> partition booting up could mistakenly assume it has quorum.  In a live
> system all corosync daemons will recognize new nodes and increase their
> "live" expected_votes accordingly.  But they won't write this back to
> the config file, leading to lack of information on reboot if they can't
> learn better from their peers.
>
> > So what I am thinking is, the first node will add nodelist with nodeid: 1
> > into its corosync.conf file.
> >
> > nodelist {
> >     node {
> >       ring0_addr: node1
> >       nodeid: 1
> >     }
> > }
> >
> > The second node to be added will get this information through some other
> > means and add itself with nodeid: 2 into it's corosync file.
> > Now the question I have is, does node1 also need to be updated with
> > information about node 2?
>
> It'd better, at least to exclude any possibility of clashing nodeids.
>
> > When i tested it locally, the cluster was up even without node1 having
> > node2 in its corosync.conf. Node2's corosync had both. If node1 doesn't
> > need to be told about node2, is there a way where we don't configure the
> > nodes but let them discover each other through the multicast IP (best
> > option).
>
> If you use IPv4 multicast and don't specify otherwise, the node IDs are
> assigned according to the ring0 addresses (IPv4 addresses are 32 bit
> integers after all).  But you still have to update expected_votes.
>
> > Assuming we should add it to keep the files in sync, what's the best way
> to
> > add the node information (either itself or other) preferably through some
> > CLI command?
>
> There's no corosync tool to update the config file.  An Augeas lense is
> provided for corosync.conf though, which should help with the task (I
> myself never tried it).  Then corosync-cfgtool -R makes all daemons in
> the cluster reload their config files.
> --
> Feri
>
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