[ClusterLabs] questions about startup fencing

Adam Spiers aspiers at suse.com
Wed Nov 29 12:51:41 EST 2017

Kristoffer Gronlund <kgronlund at suse.com> wrote:
>Adam Spiers <aspiers at suse.com> writes:
>> - The whole cluster is shut down cleanly.
>> - The whole cluster is then started up again.  (Side question: what
>>   happens if the last node to shut down is not the first to start up?
>>   How will the cluster ensure it has the most recent version of the
>>   CIB?  Without that, how would it know whether the last man standing
>>   was shut down cleanly or not?)
>This is my opinion, I don't really know what the "official" pacemaker
>stance is: There is no such thing as shutting down a cluster cleanly. A
>cluster is a process stretching over multiple nodes - if they all shut
>down, the process is gone. When you start up again, you effectively have
>a completely new cluster.

Sorry, I don't follow you at all here.  When you start the cluster up
again, the cluster config from before the shutdown is still there.
That's very far from being a completely new cluster :-)

>When starting up, how is the cluster, at any point, to know if the
>cluster it has knowledge of is the "latest" cluster?

That was exactly my question.

>The next node could have a newer version of the CIB which adds yet
>more nodes to the cluster.

Yes, exactly.  If the first node to start up was not the last man
standing, the CIB history is effectively being forked.  So how is this
issue avoided?

>The only way to bring up a cluster from being completely stopped is to
>treat it as creating a completely new cluster. The first node to start
>"creates" the cluster and later nodes join that cluster.

That's ignoring the cluster config, which persists even when the
cluster's down.

But to be clear, you picked a small side question from my original
post and answered that.  The main questions I had were about startup
fencing :-)

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