[ClusterLabs] Antw: Surprising semantics of location constraints with INFINITY score

[Ulrich Windl]

>>> Kristoffer Grönlund <kgronlund at suse.com> schrieb am 11.04.2017 um 15:30 in
Nachricht <87lgr7kr64.fsf at suse.com>:
> Hi all,
> 
> I discovered today that a location constraint with score=INFINITY
> doesn't actually restrict resources to running only on particular
> nodes. From what I can tell, the constraint assigns the score to that
> node, but doesn't change scores assigned to other nodes. So if the node
> in question happens to be offline, the resource will be started on any
> other node.

This makes sense IMHO: Otherwise the resource would not run at all. Obviously
the infinity score for a node means: "Whenever this node is available, run the
resource there (other rules not forbidding)". If you want to run the resource
nowhere else, you'd add a -INFINITY score on the other nodes, I guess.

> 
> Example:
> 
> <rsc_location id="dummy-on-node2" rsc="dummy" score="INFINITY"
node="node2"/>
> 
> If node2 is offline, I see the following:
> 
>  dummy	(ocf::heartbeat:Dummy):	Started node1
> native_color: dummy allocation score on node1: 1
> native_color: dummy allocation score on node2: -INFINITY
> native_color: dummy allocation score on webui: 0
> 
> It makes some kind of sense, but seems surprising - and the
> documentation is a bit unclear on the topic. In particular, the
> statement that a score = INFINITY means "must" is clearly not correct in
> this case. Maybe the documentation should be clarified for location
> constraints?
> 
> -- 
> // Kristoffer Grönlund
> // kgronlund at suse.com 
> 
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