> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:squirrelmail- > [EMAIL PROTECTED] On Behalf Of email builder > Sent: Thursday, May 12, 2005 7:36 PM > To: John Madden > Cc: [email protected] > Subject: Re: [SM-USERS] Re: Load Balancing and session side effect > > > --- John Madden <[EMAIL PROTECTED]> wrote: > > > We are a small biz that wants to start implementing clustering of > our > > > services, but not sure if LVS is necessary just yet. We are starting > > with > > > just two boxes with both HTTPD/SquirrelMail and MTA/IMAP on both boxes > > with > > > NFS-based backend on a 3rd machine. We'll put all mail spools and SM > > data > > > dirs and PHP sessions (file-based) on the NFS machine. > > > > > > Our question is if there will be any problems to consider starting > out > > with > > > a DNS round-robin load balancing instead of more complex LVS stuff? > > > > I suggest that you not store your mail spools on NFS. Do IMAP over the > > network to > > a load-balanced imapd if you want (with GFS on shared scsi/san storage), > > but for > > heaven's sake, don't point your imapd at an NFS export. > > If I have more than one IMAP server (at least on different machines), then > how else do I point all IMAP servers to the mail spool beside > NFS/GFS/AFS/etc? The connection from clients (SM, etc) to IMAP will of > course be regular IMAP connections/protocol. Eventually, we have our eye > on > Perdition to help load balance IMAP connections.
Regardless of what this guy says, your plan as you've outlined should work and I only say should because I personally haven't tried storing PHP session information on an NFS share before. There was some recent discussion about that on the list and I believe I saw the general consensus to be that it would only fail under very unusual circumstances (search the archives to verify though). The only real drawback is that you are relying on round-robin DNS to load balance your machines. As I mentioned earlier, if one machine fails, the RR will still send clients to that now dead IP. That may be acceptable to you until you either recover the machine or manually configure the remaining box to answer on that IP as well. We use hardware layer4 switches in front of our systems to perform automatic load balancing, health detection and failover. The particular devices we use can maintain user session to one machine or the other, negating the need to store the PHP session information on the NFS box. This is essentially filling the role of the LVS and allows us to provide very high service availability. As far as using Perdition, it wasn't really designed to be a load balancer, at least when I last used it and wouldn't really be effective at it. Your load balancing would be determined by WHO was logging in at a particular time instead of how loaded a machine was. If all the users assigned to server 1 were logged in an none assigned to server 2 you'd have one box loaded and one completely idle. I would suggest that if you get to the point where DNS load balancing isn't sufficient for your needs you take the plunge and set up a Linux load balancer or purchase a hardware switch that'll do it for you. Life is much easier that way =) If you scale even further, separate your IMAP/SMTP/HTTP servers. If you do that, you can grow the specific service that's being utilized the most without having to rebuild all services for each machine. By that time you should be bringing in enough money that cost wouldn't be prohibitive. -- Marc ------------------------------------------------------- This SF.Net email is sponsored by Oracle Space Sweepstakes Want to be the first software developer in space? Enter now for the Oracle Space Sweepstakes! http://ads.osdn.com/?ad_ids93&alloc_id281&op=click -- squirrelmail-users mailing list Posting Guidelines: http://squirrelmail.org/wiki/wiki.php?MailingListPostingGuidelines List Address: [email protected] List Archives: http://news.gmane.org/thread.php?group=gmane.mail.squirrelmail.user List Archives: http://sourceforge.net/mailarchive/forum.php?forum_id)95 List Info: https://lists.sourceforge.net/lists/listinfo/squirrelmail-users
