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Question about Pacemaker & mysql master/slave replication and DRBD replication

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coma.inf at gmail

Mar 15, 2012, 5:09 AM

Post #1 of 2 (651 views)
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Question about Pacemaker & mysql master/slave replication and DRBD replication

Hello,

I'm a new Pacemaker user and i trying to understand exactly what it can do
/ can't do in case of MySQL Replication or DRBD replication.

I have two MySQl servers, for the moment with a simple Master/Slave
replication, my need is to implement a high availability system with
automated IP and DB fail-over / fail-back (including replication).

I would like to be able to have 1 node designated as Master and in case of
failure, automatically promote the slave node to master, and when the
initial master will available again do the reverse operation automatically.

I have compared several solutions and according to my needs (i have two
servers only and i don't want / don't need use solutions like MySQL Cluster
which requires 4 servers), Pacemaker seems the best solution in my case.

I have to choose between Pacemaker with MySQL replication or Pacemaker with
DRBD replication but it's difficult to find clear explanations and
documentation about the 2 solutions, so i have some questions about it.
If anyone can enlighten me i thank in advance!

In the Pacemaker + MySQL replication case:

I know pacemaker is able to do IP failover and it seems DB failover too(?),
but what type of failure pacemaker can detect?
I know it is able to monitor the network failure (node unreachable), but
can it detect MySQL service failure and promote the slave to master?
Example: Master node reachable, but database not (mysql service stopped,
access failed->too many connexions, disk full, database read access but
write error...)?

Can pacemaker do (natively) the reverse operation automatically (When
initial master node or MySQL DB will be available again)?
In this case, can it manage the replication? and if not, can i use a
personal shell scipt to do it?

Else, i have browsing the maillinglist archives and i've seen the Percona
Replication Manager solution (
http://www.mysqlperformanceblog.com/2011/11/29/percona-replication-manager-a-solution-for-mysql-high-availability-with-replication-using-pacemaker/),

somebody he already implemented it in production environment? Is it
reliable?

In the Pacemaker + DRBD replication case:

I understand that pacemaker and drbd work very well together and drbd is a
good solution for mysql replication.
In case of master (active node) failure, pacemaker+DRBD promote
automatically the slave (passive node) as master and i have read that drbd
can handle itself the back replication when master node is available again?
can you enlighten me a little more about it?

I also read that it is recommended to have a dedicated network for drbd
replication, but can i do without? I don't write a lot on my databases,
reading much more, so replication will not be a big charge.

The big problem i have with DRBD is that i work on RHEL5 and i have read
that i will have to recompile DRBD after each kernel update (there is not a
lot of updates but still some),
is it possible to avoid it? (CentOS DRBD packages maybe?)

Somebody has already been problems with RHEL updates and DRBD/Pacemaker?

Thank you in advance for any response, and sorry if my english is not very
good.

andrew at beekhof

Mar 28, 2012, 11:18 PM

Post #2 of 2 (599 views)
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Re: Question about Pacemaker & mysql master/slave replication and DRBD replication [In reply to]

On Thu, Mar 15, 2012 at 11:09 PM, coma <coma.inf [at] gmail> wrote:
> Hello,
>
> I'm a new Pacemaker user and i trying to understand exactly what it can do /
> can't do in case of MySQL Replication or DRBD replication.
>
> I have two MySQl servers, for the moment with a simple Master/Slave
> replication, my need is to implement a high availability system with
> automated IP and DB fail-over / fail-back (including replication).
>
> I would like to be able to have 1 node designated as Master and in case of
> failure, automatically promote the slave node to master, and when the
> initial master will available again do the reverse operation automatically.
>
> I have compared several solutions and according to my needs (i have two
> servers only and i don't want / don't need use solutions like MySQL Cluster
> which requires 4 servers), Pacemaker seems the best solution in my case.
>
> I have to choose between Pacemaker with MySQL replication or Pacemaker with
> DRBD replication but it's difficult to find clear explanations and
> documentation about the 2 solutions, so i have some questions about it.
> If anyone can enlighten me i thank in advance!
>
>
> In the Pacemaker + MySQL replication case:
>
> I know pacemaker is able to do IP failover and it seems DB failover too(?),
> but what type of failure pacemaker can detect?
> I know it is able to monitor the network failure (node unreachable), but can
> it detect MySQL service failure and promote the slave to master?

Yes. We call the mysql resource agent and react to any failures it detects.

> Example: Master node reachable, but database not (mysql service stopped,
> access failed->too many connexions, disk full, database read access but
> write error...)?
>
> Can pacemaker do (natively) the reverse operation automatically (When
> initial master node or MySQL DB will be available again)?

Yes. This is what the http://www.mysqlperformanceblog.com blog is talking about.
Pacemaker doesn't actually understand what it is managing, the details
are hidden by the RA scripts.

> In this case, can it manage the replication? and if not, can i use a
> personal shell scipt to do it?
>
> Else, i have browsing the maillinglist archives and i've seen the Percona
> Replication Manager solution
> (http://www.mysqlperformanceblog.com/2011/11/29/percona-replication-manager-a-solution-for-mysql-high-availability-with-replication-using-pacemaker/),
> somebody he already implemented it in production environment? Is it
> reliable?

I've not used it myself but I hear good things.

>
>
> In the Pacemaker + DRBD replication case:
>
> I understand that pacemaker and drbd work very well together and drbd is a
> good solution for mysql replication.
> In case of master (active node) failure, pacemaker+DRBD promote
> automatically the slave (passive node) as master and i have read that drbd
> can handle itself the back replication when master node is available again?
> can you enlighten me a little more about it?
>
> I also read that it is recommended to have a dedicated network for drbd
> replication, but can i do without? I don't write a lot on my databases,
> reading much more, so replication will not be a big charge.
>
> The big problem i have with DRBD is that i work on RHEL5 and i have read
> that i will have to recompile DRBD after each kernel update (there is not a
> lot of updates but still some),
> is it possible to avoid it? (CentOS DRBD packages maybe?)
>
> Somebody has already been problems with RHEL updates and DRBD/Pacemaker?

RHEL5 is getting on a bit, its version of glib is too old to even
build pacemaker there anymore.
What about using RHEL6 which even ships with pacemaker?

>
> Thank you in advance for any response, and sorry if my english is not very
> good.
>
>
>
> _______________________________________________
> Pacemaker mailing list: Pacemaker [at] oss
> http://oss.clusterlabs.org/mailman/listinfo/pacemaker
>
> Project Home: http://www.clusterlabs.org
> Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
> Bugs: http://bugs.clusterlabs.org
>

_______________________________________________
Pacemaker mailing list: Pacemaker [at] oss
http://oss.clusterlabs.org/mailman/listinfo/pacemaker

Project Home: http://www.clusterlabs.org
Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf
Bugs: http://bugs.clusterlabs.org

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