[ClusterLabs] 2 node clusters - ipmi fencing

[Ondrej]

On 2/21/20 10:51 PM, Ricardo Esteves wrote:
> Hi,
> 
> I'm trying to understand what is the objective of the constraints to
> have the fencing devices running on opposite node or on its own node or
> running all on the same node. Can you explain the difference?
> 

Hi Ricardo,

Using the constraints you can have a better monitoring of the IPMI 
device readiness. If the 'monitor' of fence device fails then most 
probably that device will be not able to fence node when needed.
Constraints for fence devices are not required by pacemaker and 
pacemaker should be able to fence the nodes without them (if fence 
devices are configured properly).

A) Having IPMI device of nodeX monitored from nodeY gives you following 
check: 'nodeY can communicate with nodeX IPMI device and check its 
status'. If in the future the nodeY would need to fence nodeX then it 
should be able to connect to IPMI device.

B) Having IPMI device of nodeX monitored from nodeX gives you following 
check: 'nodeX can communicate with nodeX IPMI device and check its 
status'. nodeX should not fence itself for reasons mentioned in my 
previous email and also in Dan's response to this. So this monitoring 
doesn't provides you with useful information for future fencing. It is 
not required that nodeX can communicate to nodeX IPMI device for fencing.

Most important is that fencing works for both nodes when properly 
tested. Ideally try if fencing works properly. Optionally if you want 
cluster to monitor IPMI devices from node that will be using them you 
can use constraints to move fence devices to opposite node.

--
Ondrej Famera