[imp] Re: multiple IMP front ends?

[Steven Premeau]

>
>
>Has anyone implemented IMP on multiple front ends to distribute load
>> (and also for redundancy). We already have it running on one machine
>> pointing it to IMAP mail folders on another machine.
>
>
>I know of several people doing it, and I'm sure there are many more.
>

    The University of Wisconsin - Parkside is running IMP load-balanced 
across two "front-end" machines.

>HEAD has a session handling API built in so that you can share a sessions db
>between machines, but you don't need much more, and you can do that with
>RELENG_* yourself quite easily.
>
We use the LBNamed module to balance usage between the nodes.

Setup wasn't that difficult -- here's the tips and traps we noticed.

Our prefs database is stored in a MySQL database on our "big" IMAP 
server.  By configuring Horde/IMP to connect via IP to the database, all 
preferences are shared.

    We have an SSL certificate issued to the load balancing DNS name 
(best.email.uwp.edu a/k/a RangerMail.uwp.edu) the web server on both 
node refers to itself as best.email.uwp.edu.

    We changed the session cookie domain from it's default to 
".email.uwp.edu" -- even though both systems have the same name, it just 
made sessions much more stable.

    One gotcha that we haven't solved.  If a user attaches a file to a 
message composition and then "dawdles" before sending the message (by 
editing the composition or just delaying) we have had the system change 
"front-end" hosts during that delay -- because the attached files are 
placed in /tmp during composition, they are not shared between machines 
and you get lots of errors when the system goes looking for them.  

    We have worked around that by educating our users to do the 
attachment part last -- if they attach and then send, it hasn't every 
changed hosts on us.

If you would like more information on the setup at UW-Parkside, please 
let me know.

Steve.