[Pacemaker] Inter-resource communication.

[Dermot Tynan]

I've tried Googling for this, with little success. Wondering if someone 
here can help.

I am operating Pacemaker in a clone configuration with multiple nodes 
(usually between 4 and 6).  In the event that one of the nodes fails, I 
want one of the remaining nodes to perform a database update (the DB is 
in its own cluster elsewhere).

Currently, I use a resource agent which takes the notify-stop message 
and updates the DB, but this runs on all of the remaining nodes.

The two solutions that come to mind are a) to only do the update if the 
resource agent is running on the Designated Controller, but this means 
the agents need to probe around to find out which node is the DC. b) 
involves creating a new, single (manager) resource which can run on any 
one of the nodes, and which has responsibility for making the DB update. 
The problem here is synchronising the notify-stop messages sent to the 
clone resources, and somehow getting that message to the manager resource.

I'm also concerned about race conditions where either the DC or the 
Manager resource were on the failed node. If the clone notification 
happens before the DC or the Manager has been moved to a new node, they 
won't update the database.

Any thoughts?  Is there a better way to ensure that only one of the 
surviving members of the clone cluster does the DB update? Thanks.
                                     - Der

-- 
Dermot Tynan
HP Cloud
+353 91 754 224