Building redundancy

[Oliver Leitner]

On 6/1/05, Ashley M. Kirchner <ashley at pcraft.com> wrote:
> 
>     First, the question: How to build redundancy on a "users" server?
> 
>     What's behind it: When our main users server goes down, no one can
> log in to check their e-mail.  So the problem as it was presented this
> morning was to research some way to make it so that if that server goes
> down, users still have a way of getting to their e-mail or login to
> their accounts for that matter.  Now, the setup we have is a bit
> different from most people I'm sure.  Incoming e-mail flows as follows:
> 
>     Internet -> MX server -> spool server (NIS+ slave)
> 
>     Our "users" server - also our NIS+ master - (which is a totally
> different machine) does an NFS mount of the spool server on /var/mail/
> and voila, e-mail.  When our users use imap/pop to check/get/send
> e-mail, they log in to that "users" server to do so.  No one
> communicates directly with the spool server.  So when the "users" server
> goes down, no one can get to their e-mail.  The question: what kind of
> redundancy can I build so that if that server were to go down, that
> users can still log in (to -something-) and still access everything they
> need.  Presumably this would be a separate machine and that the fall
> back would be transparent to them.  I just don't know how or what.
>

besides the obvious (keeping the server running) id consider you think
about a mirroring type of system, i am not sure if anyone has yet
tried something like that for mailservers, at least for webservers its
pretty common to have 2 or 3 or more servers, who are updating their
content with each other at special given times.

first things that come into my mind when thinking on bringing that
system to a mailserver:

1. write your own mailserver (pop, imap, smtp, whatever...) and insert
a "duplicate mail to host xxx.xxx.xxx.xxx folder something..."
technic, or just change an existing opensource server to do that for
you.

2. have a non-real-time backup solution (cronjobs, caching,
whatever...) do the job on keeping them updated...

for the switch in im somehow thinking on dns, mx entry, isnt there
something like  a backup mx entry?

well, so much bout my thoughts, maybe someone else has better ideas,
anyhow, i hope i wasnt too far away from it.
> --
> H | I haven't lost my mind; it's backed up on tape somewhere.
>   +--------------------------------------------------------------------
>   Ashley M. Kirchner <mailto:ashley at pcraft.com>   .   303.442.6410 x130
>   IT Director / SysAdmin / WebSmith             .     800.441.3873 x130
>   Photo Craft Imaging                       .     3550 Arapahoe Ave. #6
>   http://www.pcraft.com ..... .  .    .       Boulder, CO 80303, U.S.A.
> 
> 
> 
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Greetings
-- 
Oliver Leitner
Technical Staff
http://www.shells.at