[ClusterLabs] Moving a resource when another resource fails

[Ken Gaillot]

On Wed, 2021-02-24 at 15:33 -0500, john tillman wrote:
> Good day all,
> 
> I'm trying to set up my cluster such that when mysql can't run, my
> VIP
> will move to another node with a working mysql.  I'm trying to do
> this
> with a location constraint but can't quite figure out the syntax.

You want colocation rather than location -- colocate the VIP with
mysql.

> I have a resource myVIP.
> simple VIP resource.  It only runs on one node at a time.  My
> applications
> connect through it to the database.
> 
> I have a resource myDB-clone that runs on two nodes.  It is simply a
> mysqld resource, cloned to the two nodes I need it on.
> 
> FYI, behind the scenes I have a master-master replication
> configuration
> but I use the VIP so that all writes go to the same DB.
> 
> According to the man page for pcs setting up the rule for this
> constraint
> requires an "expression" (or more then one).  That's where I'm having
> the
> problem.
> 
> My pcs command looks like:
> 
> pcs  constraint  location  myVIP  rule  constraint-id=Rule1 
> score=-INFINITY  <insert expression here>
> the expression I'm looking for is one that will determine if mysqld,
> myDB-clone, is running on this node and if it is not then have the
> -INFINITY score applied and move myVIP to the other node.
> 
> Any help/suggestions would be appreciated.
> 
> -John
> 
> 
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-- 
Ken Gaillot <kgaillot at redhat.com>