[ClusterLabs] Required guidance w.r.t pacemaker

[Ken Gaillot]

On Wed, 2022-06-08 at 20:28 +0530, Sridhar K wrote:
> Thanks a lot, Ken,Andrie for the time and guidance it was really
> helpful. 
> 
> will proceed with the below approach
> 
> [A preferred setup would be to run corosync and pacemaker on the VMs,
> and configure bundles for the db containers.] 
> 
> I will try to get comfortable with bundle approach , referring 
> https://wiki.clusterlabs.org/wiki/Bundle_Walk-Through
> 
> In above link, it's said at the start [Configure a test cluster of at
> least two cluster nodes with Pacemaker 1.1.17 or later]
> but in the section 
> Configure the cluster
>  Our example needs the run-command option only because we are running
> Pacemaker 1.1 inside the container:
> 
> In short, we have a pacemaker cluster with 2 nodes(i,e full stack
> pacemaker installed) and a bundle that has a  docker/podman image the
> image has only pacemaker-remote installed in it.
> i,e Line
> RUN yum install -y httpd bind-utils curl lsof wget which pacemaker
> pacemaker-remote resource-agents
> Is my understanding correct, or in the image built we have a full-
> stack pacemaker as well. 

You at least need the pacemaker-cli package as well.

The container will only run pacemaker-remoted, but it's worthwhile to
install the full pacemaker package because it has ancillary files that
are useful.

(In the just-released 2.1.3 version, the crm_attribute tool is now in
the pacemaker-cli package, so that is not as big a deal anymore.)

> 
> In case of any other links w.r.t usage of bundle/examples, Please
> share the same.

The walk-through is a good start. For fuller details, see:

https://clusterlabs.org/pacemaker/doc/2.1/Pacemaker_Explained/singlehtml/index.html#bundles-containerized-resources

> 
> Regards
> Sridhar
> 
> 
> On Wed, 8 Jun 2022 at 19:46, Andrei Borzenkov <arvidjaar at gmail.com>
> wrote:
> > 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
> > > 
> > 
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-- 
Ken Gaillot <kgaillot at redhat.com>