[Linux-HA] master slave colocation question

[Andrew Beekhof]

On Nov 12, 2007, at 2:29 PM, Cousin Marc wrote:

> Hi,
> I'm trying to figure out the actual behaviour of heartbeat (I'm using
> 2.1.2+hg.11310.702e4f418ca8-2, as provided for debian sid)
>
> I'm sorry if it's a bit long and complicated, don't hesitate to ask  
> me to
> clarify some parts ...
>
>
> I've detailed the steps I'm following, as I've found several docs in  
> the wiki
> contradicting each other.
>
> I'm trying for my tests to build a 3 node cluster (drbdtest1, 2 and  
> 3), with 2
> nodes hosting a drbd device, and one resource group having to be  
> collocated
> with the master drbd resource.
>
> First, I create a drbd resource ...
>
> No problem here. Without constraints, it's running anywhere.
>
> I'm adding a location constraint telling heartbeat not to run on  
> drbdtest3 ...
>
> cibadmin -o constraints -C -X '
> <rsc_location id="place_r0" rsc="cloner0">
>          <rule id="prefered_place_r0" score="-INFINITY">
>            <expression attribute="#uname" id="colocr0_1"  
> operation="eq"
> value="drbdtest3"/>
>          </rule>'

that will work, but you're better off with a rsc_colcation constraint  
(also set the score=-INFINITY)

> It's OK, now it's not running on the third node. It's activating a  
> master on
> drbdtest1.
>
> Then I create my resource group ('applisr0'), with no constraints  
> for now.
>
> It's OK, but of course, with no constraints, it's not running where  
> it should.
> In fact, it's running on the third node.
>
> Then I put a constraint telling it not to run on a stopped node.
>
> cibadmin -o constraints -C -X '<rsc_colocation  
> id="r0_et_applis_stopped"
> from="applisr0" to="cloner0" to_role="stopped" score="-INFINITY"/>
>
> It's not working. The group is still trying to start on the third  
> node.

Instead of a double negative, just go with a positive:

cibadmin -o constraints -C -X '<rsc_colocation id="r0_et_applis"   
from="applisr0" to="cloner0" score="INFINITY"/>

> I've tried a lot of other configurations. I think that 'stopped' is  
> not
> working...
>
> The most obvious way to verify it is this :
>
> if I replace the previous constraint with :
> cibadmin -o constraints -U -X '<rsc_colocation  
> id="r0_et_applis_stopped"
> from="applisr0" to="cloner0" to_role="stopped" score="+INFINITY"/>'
>
> the resource isn't running anywhere. I think it means that every  
> node is
> considered to be in the stopped role.
>
>
> I can make it work this way :
>
> cibadmin -o constraints -C -X '<rsc_colocation  
> id="r0_et_applis_master"
> from="applisr0" to="cloner0" to_role="master" score="+INFINITY"/>'
>
>
> So, to sum it up, it seems to me that the stopped role is seen as  
> true on
> every node...
>
> Am I right ?

For clones, this may be correct.
Most people find the regular way sufficient but there's no argument  
that the double negative should also work.

If you'd like to log a bug in bugzilla I will make sure it gets fixed.


> I would rather have a configuration where I tell heartbeat what it  
> cannot do
> and leave it as free as possible (as I've seen in most examples),  
> instead of
> forcing it.
>
> BTW, I was using this doc : http://linux-ha.org/v2/Concepts/MultiState