Backup mail server?

[Scot L. Harris]

On Tue, 2005-05-17 at 07:50, Ted Beaton wrote:

> How about this?  Have 2 mail servers.  The backup kept in sync w/ the 
> primary using rsync or something along that line.  Only the primary is 
> in the dns.  Have a script on your dns ping the primary mail server and 
> if it gets a response do nothing.  If it doesn't get a response the 
> script then edits the db files on the dns server, changes the serial 
> number in the files and restarts named.  The backup is now the primary. 
>   Or to be a little more sophisticated you could have the script query 
> the primary mail server with an expect script using esmtp.  This makes 
> sure that esmtp is responding not just that the primary mail server is 
> still on the network.  You need to be running your own dns and mail 
> servers to do this.  I haven't had the time to do this myself but I know 
> that my boss would go ballistic if he didn't have email for more than a 
> couple hours.  Of course he doesn't want to pay for HA.  It was all I 
> could do to get a Dell 1750 with raid 5 and dual power supplies to build 
> my mail server on.  Email is his lifeline and he considers it critical.

What do you have the time to live set to in DNS for your MX records? 
Modifying DNS can cause significant delays until the new information is
propagated across the Internet.  This is some what controlled by the
time to live value set in your DNS.  

If you have two mail servers that you maintain set them up with equal MX
records and email will flow though both of them.  If one goes down there
will be a slight delay as the sender retries.  The delay will be
controlled by the sender.  If you modify the DNS files as suggested the
sender may not read the new MX info for some time depending on the TTL
of the MX and how long their system caches the info.

Of course if email is really that important I assume you have your email
servers at different locations with different ISPs.  

If he is not willing to pay for HA then it must not really be critical. 
-- 
Scot L. Harris
webid at cfl.rr.com

Advancement in position.