Cluster or backup

[Adrian]

Hi everybody,

We're currently running only one mail server with AMS, and we are evaluating how to ensure availability of email services with a second server.
We're trying to decide if we implement a second server running as a backup mail server, or 2 servers running clustered.

We can't get some straight guides on any of these subjects. We've searched these forums but found no sufficient information.
Can we get some help and advice from the experts?

Thanks guys.

[rob]

A backup server will only ensure incoming emails are not lost and held in storage until your primary mail server comes online. To ensure all services are active then clustering is the best option.

To setup a clustering system:-

- Ensure you move your accounts directory into a network storage device (SAN) that both mail servers can access.
- Both servers should be setup to share this same accounts directory.
- The second mail server will need to setup its services seperately.
- At the point of entry to the clustering system, you should use a virtual server which will distribute incoming connections amongst the 2 servers.

I should note that there a couple of limiations on clustering. Firstly the SPAM databases cannot share the same data and so each will maintain its own data (this is more of an issue on the bayesian filter). The other is that WebMail is not recommend to run behind a virtual server. Instead, you should try to distribute your users amongst the 2 webmail interfaces, either by providing multiple IP addresses at the DNS for your WebMail domain or using a web script to randomly spread users who access a generic login page to the 2 different webmail domains.

[Adrian]

Hi Rob. I think we'll test the backup server approach.

In order to do this, how should we configure the DNSs servers?
Do we need to set up the same domains and user accounts on both servers, and then do POP retrieval from the main server from the backupo server?

Thanks again!

[Adrian]

Hi guys,

Any help please?
Thanks!

[rob]

Fortunately the backup server is quite a simple setup. Basically ensure you create backup domains for all your domains on the primary server, then create static routes which direct mail for those domains to the primary server, setting teh queue life to be extended for a few days (this will effectively be maximum down time on the primary server). The final step is to set the DNS records of all your domains to include a MX entry for the backup server, with a higher value than the primary MX records. What will essentially then happen is that incoming mail will go directly to primary server, but if they can't connect, they will deliver it to hte backup server. The backup server will then hold the mails and until the queue life expires or it can get the mails into the primary server.

[Adrian]

Hi guys, we just managed to get some time and test this.
Everything went well with the backup server, except for this: when the secondary (backup) server receives the email sent to the primary one (because it is down), it gets MX records from DNS and tries to deliver these emails to the primary server. As it is dow, it delivers all email... to itself! So when it reaches sever hops, it deletes these emails.
We've set static routes as you told, but I believe we're missing something.
I think the backup server should only try to deliver to the primary, and not to itself.

Can you tell us what to do?

And one more question: do we need to set up static routes for each backup domain we have, or can we use a simple "*" or something to tell the backup server that the same route should be used for all domains?

Thanks again!

[rob]

When creating these kind of backup servers, you must also create a static route for the domain. Basically in the outgoing mail service, create a static route for the domains you are hosting and ensure they force mail to route only to the primary server. This will avoid the MX lookup and ensure it doesnt loop the mail to itsself. If the backup server is purely to send mail to the primary server (not any other location), then you can avoid static routes all toghter and set the main outoging mail service settings to route all mail to the primary server (relaying settings).

[Adrian]

Thanks Rob, the next question is how to tell AMS to deliver only to the primary mail server.
Thanks again!

[rob]

Posting my response to an email here for reference...

You should ensure that the static route is spelt correctly and that the relaying settings are filled in correctly. Of course you should create a static route for all the required sub domains too (ensure the static route matches all the portions after the @ symbol in the valid email addresses).