Re: dbmail + geo-replication

Hello Ryan,


The way I achieve this through dbmail is by using a replica mysql 
cluster as a back-end database

In practical terms you set up the 2 sites each with a mysql DB and 
configure them for mutual replication. On top you have 1 dbmail instance 
deployed at each site that points to its respective database.

In my case I have also a Linux Virtual Server load balancer in front of 
the cluster with a Virtual IP used by my clients to connect to dbmail.


In this manner you can also periodically shutdown one of the 2 replicas. 
Once the replica is brought back on-line mysql automatically resumes 
replication.

I hope this helps,

Mauro


On 21/09/18 04:26, Ryan Beethe wrote:
> I am currently operating a small mail server (postfix + dovecot) but I
> have experienced a couple of ISP issues recently and would like to
> improve the availability of my server by operating a second server at a
> separate physical site (the sites I have available are separated by a
> 60ms ping).
>
> I am new to the world of high availability, but given my resources and
> constraints, an "active/passive" configuration seems to be my best
> option, where I have a primary server that is up most of the time and I
> can use pacemaker to switch from one to the other for failovers.
>
> I think I could get away with not using a distributed file system if I
> were to switch from dovecot to dbmail.  I definitely need the
> distributed database, so avoid also using a distributed file system
> seems like a way to keep my architecture as simple as possible (but
> please correct me if I am wrong).
>
> For doing geo-replication, I have read that galera supports
> georeplication.  But my gut sense is that galera's synchronous protocol
> in combination with my ping time would make anything that needed to
> write to the database a lot (like dbmail) prohibitively slow.  Does
> anybody know if that is the case or not?
>
> Also, I read that auto_increment columns with the galera plugin are
> guaranteed to be unique, but not guaranteed to be sequential.  Would
> that break dbmail?
>
> My other option would be a master-master synchronization between the two
> databases.  I know people on this mailing list have been doing that for
> a while, because I read about that setup on this mailing list as far
> back as 2006.  But (noob question alert), since the master-master
> database sync is asynchronous, doesn't that run the risk of data loss or
> corruption from the very latest data if a server crashes?  Has that ever
> happened to any of you with dbmail, and what is the recover process
> like?
>
> Ryan
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