[ClusterLabs] question about dc-deadtime

[Ken Gaillot]

On 12/15/2016 02:00 PM, Chris Walker wrote:
> Hello,
> 
> I have a quick question about dc-deadtime.  I believe that Digimer and
> others on this list might have already addressed this, but I want to
> make sure I'm not missing something.
> 
> If my understanding is correct, dc-deadtime sets the amount of time that
> must elapse before a cluster is formed (DC is elected, etc), regardless
> of which nodes have joined the cluster.  In other words, even if all
> nodes that are explicitly enumerated in the nodelist section have
> started Pacemaker, they will still wait dc-deadtime before forming a
> cluster.  
> 
> In my case, I have a two-node cluster on which I'd like to allow a
> pretty long time (~5 minutes) for both nodes to join before giving up on
> them.  However, if they both join quickly, I'd like to proceed to form a
> cluster immediately; I don't want to wait for the full five minutes to
> elapse before forming a cluster.  Further, if a node doesn't respond
> within five minutes, I want to fence it and start resources on the node
> that is up.

Pacemaker+corosync behaves as you describe by default.

dc-deadtime is how long to wait for an election to finish, but if the
election finishes sooner than that (i.e. a DC is elected), it stops
waiting. It doesn't even wait for all nodes, just a quorum.

Also, with startup-fencing=true (the default), any unseen nodes will be
fenced, and the remaining nodes will proceed to host resources. Of
course, it needs quorum for this, too.

With two nodes, quorum is handled specially, but that's a different topic.

> With Pacemaker/Heartbeat, the initdead parameter did exactly what I
> want, but I don't see any way to do this with Pacemaker/Corosync.  From
> reading other posts, it looks like people use an external agent to start
> HA daemons once nodes are up ... is this a correct understanding?
> 
> Thanks very much,
> Chris