Server Fault Asked by VanHackman on December 30, 2021
I’m needing to set up a remote mirror for a postfix server (where the content of both mail servers should be the same at any time).
The idea is that if the main server comes down at some point the mirror server will take its place, manage the new incoming mails, and when the e-mail server comes up again, it will update it with the new e-mails and return it the control to manage the new incoming mails.
The mail servers will be hosted in different places (i.e. maindomain.com, themirrorsite.com).
Getting a simple back-up server doesn’t seem too difficult:
But the problem is that this configuration wouldn’t make the back-up site a complete mirror of the main mail server (it will hold only the e-mails received while the main server is down).
Is there a way to achieve the required configuration?
It seems data replication is the issue? UPenn has put out an interesting piece of software that works at the user level that looks interesting. It's called Unison. It might be helpful.
https://www.cis.upenn.edu/~bcpierce/unison/
I'm not sure if it would be good enough since it doesn't work at the block level.
Answered by Curtis Maurand on December 30, 2021
I'm not aware of a conventional clustering approach which would be applicable here.
For incoming mail, the solution would be multiple servers (active-active with the same MX priority).
For outgoing mail then a VIP for the SMTP service (this is also an alternative solution for the incoming mail) or using haproxy configured to find a working service as an intermediary.
That only leaves the issue of mail queued on the server.
Answered by symcbean on December 30, 2021
I've used dbmail to accomplish a similar solution. dbmail stores all the email in a database. You can setup database replication to make sure that your emails are also stored in the remote location. It makes management of the mail system more complicated as you have to manage the database as well as the email.
Answered by Yavor Shahpasov on December 30, 2021
You can achieve this by MX DNS failover + a data replication system.
For MX failover: Two mail servers, need help with dns configuration for the backup one
For data replication: http://www.drbd.org/docs/install/
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Answered by SparX on December 30, 2021
The outcome you want to achieve, and the manner in which you have decided to do it, are very different things. To be blunt, what you want to implement is a bad idea, and if you can somehow manage to make it work, it won't work for very long (or very well).
What makes this question difficult to answer is that you've leapt straight to the implementation, and haven't described anything useful about your environment or what you're trying to actually achieve. Please don't do that, you'll get a lot better results here if you "show your working".
Let me posit a couple of scenarios, though, to give you a taste of what's possible, practical, and useful:
Basically, the latter option is painful and annoying. My personal preference, if you can get away with it (and you'd be surprised how often you can) is to put all your eggs in one basket, after making sure you've got a really good, sturdy basket (proper systems engineering), keeping a stock of basket-patches and tools on hand (focusing on High Recoverability), and ensuring that people know that every once in a while, a few eggs might get broken and you're really sorry but life isn't perfect (don't make SLA guarantees that aren't reasonable).
There are times when you need ultra high availability, and I've built systems that ensure it, but they're not simple, and in many cases they're not cost-effective, which is what we're here for. Yes, HA is cool and sexy, and you get geek cred for building some towering monstrosity of complexity, but we're not here to stroke our egos. We're here to deliver business value, and I'm sorry, but a Rube Goldberg highly-available multi-site mail cluster isn't likely to be providing as much value as a simple, robust mail service and the occasional "we're sorry for the mail outage, we'll have the systems back in an hour, please feel free to have a coffee and a muffin on us" announcement.
Answered by womble on December 30, 2021
What you want is Postfix replication, which I don't think Postfix supports natively. The solution I've seen other people using is replicating the Postfix data files between servers using a distributed file system.
Answered by Klox on December 30, 2021
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