[ClusterLabs] MySQL cluster with auto failover

[Damiano Giuliani]

Unfortunately I move to a different company and they are stick to MySQL

For what I understand they have some mysql cluster without automatic
failover.
Probably also their customers have some kind of cluster without automatic
failover.

Looking at some Galera cluster designs on web seems a couple of server
proxy are placed in front.

If I would have only 3 nodes where I clustered MySQL with galera how then I
have to point my application to the right nodes?


On Wed, Sep 6, 2023, 1:32 PM Antony Stone <Antony.Stone at ha.open.source.it>
wrote:

> On Wednesday 06 September 2023 at 12:10:23, Damiano Giuliani wrote:
>
> > Thanks for helping me.
> >
> > I'm going to know more about Galera.
> > What I don't like is seems I need many nodes, at least 3 for the cluster
> > and then at least 2 other nodes for proxy.
>
> You didn't mention anything about wanting a proxy service in your original
> posting, and there's no reason why a proxy can't run on the same machines
> as
> MySQL does.
>
> As for requiring three nodes, you'll need that for pacemaker anyway.
> Trying
> to run a 2-node cluster (of anything) as a production service is a
> disaster
> waiting to happen.  Read up about "split brain" if you do not know why.
>
> > Asking for 5 VM is quite consuming.
>
> What's your actual (functional) requirement here?
>
> > As you told drbd can work only in 2 node cluster and disk replication is
> > not dbms replication.
> > Probably I'm going to try drbd on very small and low usage db.
>
> The lower the usage (and therefore unrepresentative of typical production
> activity), the more likely it is that you'll think "this is working".
>
> Assuming you mean to set up two MySQL servers each pointing at a
> synchronised
> DRBD storage volume on their local systems, the main thing I expect to go
> wrong is data cached in memory, perhaps during complex updates.
>
> If instead you mean to have only one instance of MySQL running at any
> given
> time, and a failover involves stopping MySQL on the first node and then
> starting it on the second, then sure, that will work, but it introduces a
> (probably multi-second at the very least) delay during which no client
> requests can be processed during the failover, whereas a replicated Galera
> cluster (especially with something like ProxySQL in front of it) offers
> almost
> instantaneous switchover and therefore much reduced downtime in DB
> availability.
>
> > More I know about MySQL  more postgresql seems have better replication at
> > least for me.
>
> So why not use Postgres?
>
>
> Antony.
>
> --
> I don't know, maybe if we all waited then cosmic rays would write all our
> software for us. Of course it might take a while.
>
>  - Ron Minnich, Los Alamos National Laboratory
>
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