On Thu, 20 Mar 2003, Gordon Messmer wrote:
The new system cost about $15000. It is built with an NFS backend running Red Hat Linux 7.3 on a 1TB RAID 5 set attached to a 3ware 7500 card, one 1.8 Ghz CPU and 1GB of RAM. There are two Courier servers configured identically, load balanced with DNS round-robin. Each has an
I would strongly suggest taking a good look at: http://www.linuxvirtualserver.org/Documents.html
I'm well aware of LVS techniques. I can't, however, see fit to justify throwing in two servers (without failover, LVS becomes a single point of failure) in order to provide load-balancing and fail-over to two other servers.
At some point that will likely change, but when it does the LVS boxes will be providing service to other services in the network, like our LDAP boxes, in addition to the email servers.
DNS round-robin has /so/ many problems -- you have to set the ttl incredibly low for it to work at all
That's not correct. "ping mail-test.real.com" ten times and you should get about half of the lookups to one box, and half to the other.
and /many/ email clients /cache/ the IP beyond the ttl. Thus, if you name your servers A and B, and A goes down (and A is the "primary"), many clients will continue trying to contact A despite it being down and the ttl having long expired.
There's no "primary" in a round-robin. Each server is equal. Clients that we've tested work as intended in the event of failure. HA will be introduced later on.
The LVR/NAT and LVS/DR solutions are much "better" from a high level perspective. Heck, you could probably get away with a Pentium 200 level machine as the NAT/DR "router" - it just passes and mangles packets.
What sense does it make to spend 15K on a cluster of boxes and then skimp on the HA gateways?
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