[ClusterLabs] Required guidance w.r.t pacemaker

[Andrei Borzenkov]

On 08.06.2022 17:01, Ken Gaillot wrote:
> On Wed, 2022-06-08 at 18:31 +0530, Sridhar K wrote:
>> Hi Team,
>>
>> Required guidance w.r.t below problem statement
>>
>> Need to have a HA setup for SQLServer running as a docker container
>> and HA managed by the Pacemaker which is running as a separate docker
>> container.
>>
>> I have done a setup where pacemaker and SQL Server are running as a
>> single docker container, able to achieve HA.
>>
>> How to achieve the same when Pacemaker , and Sqlserver are running in
>> different containers.
> 
> I suspect it's not feasible.
> 
> At a minimum, the Pacemaker container needs to run corosync as well as
> pacemaker (implying a custom pid 1 script that starts both) and needs
> to be privileged. I'm not sure corosync has been successfully
> containerized before.
> 
> Bundles won't work because they can only run on Pacemaker nodes.
> 
> The db container could be configured as a remote node, basically
> reproducing how a bundle is created internally. The db container would
> be configured with pacemaker-remoted as its pid 1, and an IP given to
> it that both pacemaker containers can reach. Launching all the
> containers would need to be done by the OS at boot or manually.
> 
> An ocf:pacemaker:remote resource would be configured in the cluster to
> allow the pacemaker containers to manage the db via pacemaker-remoted
> in the db containers.
> 
> A custom fence agent would be needed to allow a pacemaker container to
> ask the VM to reboot (kill and relaunch) any other container. Each VM

Actually there is fence_docker which should work in this case.

> and VM host would become a single point of failure unless a pacemaker
> container could fence the VM and then the host as fallback fence
> mechanisms in a topology.
> 
> E.g. try to fence the container -> if that fails, try to fence the VM
> -> if that fails, try to fence the host. Without all of that working,
> something becomes a single point of failure.
> 
> A preferred setup would be to run corosync and pacemaker on the VMs,
> and configure bundles for the db containers.
> 
>>
>> Checked remote node,bundle  concepts in Pacemaker unable to make HA
>> setup work.
>>
>> Please let me know whether the above scenario can be handled, any
>> links, examples would be of great help.
>>
>> Attaching a picture that depicts the scenario.
>>
>> Please do the needful, Thank you
>>
>> Regards
>> Sridhar
>