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Hi, Andrew

Let me answer your questions.

This agent is active/active which actually marks one of the node as
'pseudo'-master which is used as a target for other nodes to join to. We
also check which node is a master and use it in monitor action to check
whether this node is clustered with this 'master' node. When we do cluster
bootstrap, we need to decide which node to mark as a master node. Then,
when it starts (actually, promotes), we can finally pick its name through
notification mechanism and ask other nodes to join this cluster.

Regarding disconnect_node+forget_cluster_node this is quite simple - we
need to eject node from the cluster. Otherwise it is mentioned in the list
of cluster nodes and a lot of cluster actions, e.g. list_queues, will hang
forever as well as forget_cluster_node action.

We also handle this case whenever a node leaves the cluster. If you
remember, I wrote an email to Pacemaker ML regarding getting notifications
on node unjoin event '[openstack-dev] [Fuel][Pacemaker][HA] Notifying
clones of offline nodes'. So we went another way and added a dbus daemon
listener that does the same when node lefts corosync cluster (we know that
this is a little bit racy, but disconnect+forget actions pair is
idempotent).

Regarding notification commands - we changed behaviour to the one that
fitter our use cases better and passed our destructive tests. It could be
Pacemaker-version dependent, so I agree we should consider changing this
behaviour. But so far it worked for us.

On Wed, Nov 11, 2015 at 2:12 PM, Andrew Beekhof <abeekhof at redhat.com> wrote:

>
> > On 11 Nov 2015, at 6:26 PM, bdobrelia at mirantis.com wrote:
> >
> > Thank you Andrew.
> > Answers below.
> > >>>
> > Sounds interesting, can you give any comment about how it differs to the
> other[i] upstream agent?
> > Am I right that this one is effectively A/P and wont function without
> some kind of shared storage?
> > Any particular reason you went down this path instead of full A/A?
> >
> > [i]
> >
> https://github.com/ClusterLabs/resource-agents/blob/master/heartbeat/rabbitmq-cluster
> > <<<
> > It is based on multistate clone notifications. It requries nothing
> shared but Corosync info base CIB where all Pacemaker resources stored
> anyway.
> > And it is fully A/A.
>
> Oh!  So I should skip the A/P parts before "Auto-configuration of a
> cluster with a Pacemaker”?
> Is the idea that the master mode is for picking a node to bootstrap the
> cluster?
>
> If so I don’t believe that should be necessary provided you specify
> ordered=true for the clone.
> This allows you to assume in the agent that your instance is the only one
> currently changing state (by starting or stopping).
> I notice that rabbitmq.com explicitly sets this to false… any particular
> reason?
>
>
> Regarding the pcs command to create the resource, you can simplify it to:
>
> pcs resource create --force --master p_rabbitmq-server
> ocf:rabbitmq:rabbitmq-server-ha \
>   erlang_cookie=DPMDALGUKEOMPTHWPYKC node_port=5672 \
>   op monitor interval=30 timeout=60 \
>   op monitor interval=27 role=Master timeout=60 \
>   op monitor interval=103 role=Slave timeout=60 OCF_CHECK_LEVEL=30 \
>   meta notify=true ordered=false interleave=true master-max=1
> master-node-max=1
>
> If you update the stop/start/notify/promote/demote timeouts in the agent’s
> metadata.
>
>
> Lines 1602,1565,1621,1632,1657, and 1678 have the notify command returning
> an error.
> Was this logic tested? Because pacemaker does not currently support/allow
> notify actions to fail.
> IIRC pacemaker simply ignores them.
>
> Modifying the resource state in notifications is also highly unusual.
> What was the reason for that?
>
> I notice that on node down, this agent makes disconnect_node and
> forget_cluster_node calls.
> The other upstream agent does not, do you have any information about the
> bad things that might happen as a result?
>
> Basically I’m looking for what each option does differently/better with a
> view to converging on a single implementation.
> I don’t much care in which location it lives.
>
> I’m CC’ing the other upstream maintainer, it would be good if you guys
> could have a chat :-)
>
> > All running rabbit nodes may process AMQP connections. Master state is
> only for a cluster initial point at wich other slaves may join to it.
> > Note, here you can find events flow charts as well [0]
> > [0] https://www.rabbitmq.com/pacemaker.html
> > Regards,
> > Bogdan
> >
> __________________________________________________________________________
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>
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-- 
Yours Faithfully,
Vladimir Kuklin,
Fuel Library Tech Lead,
Mirantis, Inc.
+7 (495) 640-49-04
+7 (926) 702-39-68
Skype kuklinvv
35bk3, Vorontsovskaya Str.
Moscow, Russia,
www.mirantis.com <http://www.mirantis.ru/>
www.mirantis.ru
vkuklin at mirantis.com
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