[ClusterLabs] 2-Node Cluster - fencing with just one node running ?

[Andrei Borzenkov]

On 04.08.2022 16:06, Lentes, Bernd wrote:
> 
> ----- On 4 Aug, 2022, at 00:27, Reid Wahl nwahl at redhat.com wrote:
> 
>>
>> Such constraints are unnecessary.
>>
>> Let's say we have two stonith devices called "fence_dev1" and
>> "fence_dev2" that fence nodes 1 and 2, respectively. If node 2 needs
>> to be fenced, and fence_dev2 is running on node 2, node 1 will still
>> use fence_dev2 to fence node 2. The current location of the stonith
>> device only tells us which node is running the recurring monitor
>> operation for that stonith device. The device is available to ALL
>> nodes, unless it's disabled or it's banned from a given node. So these
>> constraints serve no purpose in most cases.
> 
> Would do you mean by "banned" ? "crm resource ban ..." ?
> Is that something different than a location constraint ?
> 

"crm resource ban" creates location constraint, but not every location
constraint is created by "crm resource ban".

>> If you ban fence_dev2 from node 1, then node 1 won't be able to use
>> fence_dev2 to fence node 2. Likewise, if you ban fence_dev1 from node
>> 1, then node 1 won't be able to use fence_dev1 to fence itself.
>> Usually that's unnecessary anyway, but it may be preferable to power
>> ourselves off if we're the last remaining node and a stop operation
>> fails.
> So banning a fencing device from a node means that this node can't use the fencing device ?
>  

Correct. Node where fencing device is not allowed cannot be selected to
use this fencing device to perform fencing.