[ClusterLabs] Question about ping nodes

[Andrei Borzenkov]

On 17.04.2021 23:01, Antony Stone wrote:
> On Saturday 17 April 2021 at 21:41:16, Piotr Kandziora wrote:
> 
>> Hi,
>>
>> Hope some guru will advise here ;)
>>
>> I've got two nodes cluster with some resource placement dependent on ping
>> node visibility (
>> https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/ht
>> ml/high_availability_add-on_reference/s1-moving_resources_due_to_connectivi
>> ty_changes-haar ).
>>
>> Is it possible to do nothing with these resources when both nodes do not
>> have access to the ping node?
> 
> The whole purpose of a ping node is to give a resource node confidence that it 
> can safely provide resources to the network.  If it loses connectivity to the 
> ping node, it considers itself dead / offline / non-functional.
> 
> If both resource nodes lose contact with the ping node, then neither of them 
> have the confidence to provide resources, so both of them stop doing so.
> 

Resource may provide services local to cluster itself or to cluster
location, so while it may be preferable to have resource active on node
with better external connectivity, it does not mean resource is
completely useless when this connectivity is not present.

> All I can say is that if this is possible then either your resource nodes have 
> poor network connectivity and should not be used as resource nodes, or else 
> the ping node has poor reachability and should not be used as a ping node.
> 
>> Currently, when the ping node is unavailable (node itself becomes
>> unavailable) both nodes stop the resources.
> 
> This is correct.  Neither node can tell whether it should take charge of the 
> resources, so for the sake of safety, they both decline to do so.
> 
> Two node clusters are intrinsically fragile in this respect.
> 
> 
> Antony.
>