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ed wrote:
Hi, Im very new to clustering. I have perhaps a very simple question:
I have to provide a email service, but with low spec computers which
we have in abndance. The service is Qmail, which we currently have
running on three boxes, each with different IP address and each have a
seperate MX record.
Now, I assume that the email service running behind a LVS will use a
single MX IP address x.x.x.x.
Right... your director (the load balancer) will probably just have one
IP address available to the external world.
However, I have not got a clue how to go about this. Should I aim to
have two single computers linked via a serial interface (for heart
beat), or should I do something more adventurous such as link them via a
network interface.
Depends on what your goal is -- see below.
We have 4,000 domains to look after, currently we just do forwarding,
which is not at all intensive. Once the spam and virus scanning kicks in
its a huge latency on the mail, scanning takes about 1.3 seconds per
mail, with the current load of four domains (which catch all). I hate to
think what this will be like with the other domains also.
My main objective with this is to allow myself to add computers on the
fly to the LVS pool so that I do not run the risk of bringing down the
network of email boxes when something needs an upgrade.
So it looks like your goal here is to provide failover and to split up
processing load between computers. Sounds reasonable. The biggest
problem you're probably going to have is shared storage. If you have,
for instance, users retrieving mail via POP3 and sending via SMTP, a
user connecting via POP3 to one real server will have to be able to get
mail that was delivered by another real server. So you probably need
somewhere to keep the mailboxes that all real servers can get to. If you
use qmail's Maildir format, which works over nfs, you can set up an nfs
server, but 1) it *might* have a heavy load, and 2) it's a single point
of failure. You'll also probably want something to replicate settings
between your real servers (qmail's control files, spam and AV
configuration files, mailbox config info, etc.) That will probably take
a whole bunch more work than just getting the LVS part working.
Josh Tolley
Raintree Systems, Inc.
http://www.raintreeinc.com
760 509 9000
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