Linux – Move mail server to a new server with no downtime

domain-name-systemdovecotemaillinux

We have a server that currently acts as a web, database and mail server. We would like to move mail to its own dedicated server.

So:

The address for the mail server is mail.example.com. It has A and MX records pointing to server1.
We want to point the A and MX records to server2 while maintaining mail.example.com as the address for the new mail server.

Once we make the change, there will be a DNS propagation period where some mail will still be delivered to server1 while everyone that has updated DNS records will be correctly delivering to server2.

Is there some way of getting our old server (server1) to respond to any mail requests with something like: "I am no longer accepting mail. Send it to server2's IP address instead. Please update your DNS records and resend". That way the sender sees the new IP address and reroutes the mail to server2. This would essentially mean no downtime whatsoever.

Is that possible?

Best Answer

Yes, you can make your server send a 450 response, which will make the sending smtp server retry later, hopefully after DNS has propagated. But why not reconfigure the old server to forward incoming mail to the new one instead?

Related Solutions

Linux – Postfix – how to retry delivery of mail in queue

According to postqueue(1) you can simply run postqueue -f to flush your mail queue. If the mails aren't delivered after flushing the queue but are being requeued instead, you might want to check your mail logs for errors.

Taking a peek at postsuper(1) might also be helpful. Maybe the messages are on hold and need to be released first.

Server Migration – Redirect to New IP Without Downtime

Here's the method that worked for me:

Sync the files and databases with the new server.
Perform a re-sync just before cut-off.
Change the DNS to point to the new server.
Forward the request coming to the old ip to the new server until DNS propagation completes.

Here's how I would do the step 4:

We will configure IPTables on a Linux server to redirect all the traffic coming on port 80, (which is the default web server port), to a server with the IP 122.164.34.240. The first step is to set your Linux box to allow this kind of forwarding to take place. Open a terminal window, log in as root user and run the following command:

# echo 1 >/proc/sys/net/ipv4/ip_forward

The next step is to tell IPTables to redirect the traffic to the new server:

# iptables -t nat -A PREROUTING -p tcp --dport 80 -j DNAT --to-destination 122.164.34.240

Here’s where the IPTables magic happens. With the third and final step, we tell IPTables to rewrite the origin of connections to the new server’s port 80 to appear to come from the old server.

# iptables -t nat -A POSTROUTING -p tcp -d 122.164.34.240 --dport 80 -j MASQUERADE

The final step is required because if we don’t tell the web server of the new server that the connections are coming from the client machines, it would think that they are originating from the old server.

You may want to repeat this for the databases and email server port as well.

Best Answer

Related Solutions

Linux – Postfix – how to retry delivery of mail in queue

Server Migration – Redirect to New IP Without Downtime

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