Load Balancing In Linux?

depam · 07-07-2006, 03:31 AM

Hi! I've noticed that when you ping www.yahoo.com and ping it again, you will get different IPs. How do they do this? I have a theory that they've included it on their DNS entries such as www1.yahoo.com, www2.yahoo.com, www3.yahoo.com, etc. However, I am also thinking they've done this to balance the load on the servers. If this can be done in linux, how can I do it? I have my own mail server and would like to balance the load on each servers by having two running servers which can be act as both POP and SMTP.

acid_kewpie · 07-07-2006, 03:59 AM

it's a round robin DNS, which most DNS servers can do just fine. Often large sites will use the geographical location of the source address (you) to point you towards a local server to, to spread it around multiple data centres. just check out BIND for round robin dns.

Tinkster · 07-07-2006, 04:29 AM

Quote:

Originally Posted by depam

If this can be done in linux, how can I do it? I have my own mail server and would like to balance the load on each servers by having two running servers which can be act as both POP and SMTP.

How many mails a day are you processing to require load-balancing?
And what hardware & which MTA are you using?

Cheers,
Tink

depam · 07-07-2006, 10:22 AM

Our company is using a single PC for the mail server. Having the following specs:

P4 3.2 LGA
120 GB Sata Drive
2 GB DDR Ram

We use xmail for receiving and exim for sending. We have an average of 1000+ mails per day (SMTP and POP).

I am just curious how I can do that?

acid_kewpie · 07-07-2006, 10:34 AM

i'm lost.... how do you expect to dns load balancing with one server??

if you wish to spread email across two servers then you'd actually use MX records with equal priorites, not necessarily dns round robins anyway.

Tinkster · 07-07-2006, 04:13 PM

Quote:

Originally Posted by depam

Our company is using a single PC for the mail server. Having the following specs:

P4 3.2 LGA
120 GB Sata Drive
2 GB DDR Ram

We use xmail for receiving and exim for sending. We have an average of 1000+ mails per day (SMTP and POP).

I am just curious how I can do that?

Acid can't see how the balancing will work, and I can't
see a need for it. We're processing around 30+ K incoming
& outgoing mails off a single Sparc 550MHz machine with
with 2GB RAM. Internally we use Groupwise.

Cheers,
Tink

acid_kewpie · 07-07-2006, 04:46 PM

Quote:

Originally Posted by Tinkster

Acid can't see how the balancing will work, and I can't
see a need for it. We're processing around 30+ K incoming
& outgoing mails off a single Sparc 550MHz machine with
with 2GB RAM. Internally we use Groupwise.

yeah all that, but then it is nice to know you have a 100% proven resilient infrastructure. active/passive or active/on-a-tape or active/oooh-bloody-hell are fine while they work, but knowing for sure that two boxes are concurrently performing as expected on a minute by minute basis is a great thing to know!

Tinkster · 07-07-2006, 10:59 PM

Quote:

Originally Posted by acid_kewpie

yeah all that, but then it is nice to know you have a 100% proven resilient infrastructure. active/passive or active/on-a-tape or active/oooh-bloody-hell are fine while they work, but knowing for sure that two boxes are concurrently performing as expected on a minute by minute basis is a great thing to know!

True enough, and we have another machine with identical set-up
for fail-over.
But he was explicitly asking about load-balancing which
seems like overkill with that workload.

Cheers,
Tink

depam · 07-08-2006, 11:09 AM

Guys,

do you think the setup is overkill for the mail server? Another thing that I've noticed with our mail server is that even though it is already 2GB Mem, I still consume 99% of its memory.

KimVette · 07-08-2006, 01:40 PM

depam,

What is consuming all the memory? Allocated memory does not mean it's running out. Here's the output from my machine:

Code:

             total       used       free     shared    buffers     cached
Mem:          2025       1954         71          0         66        906
-/+ buffers/cache:        980       1044
Swap:         1961          3       1957

At first glance it appears that 1954/2025=96.4% of RAM in my machine is used, leaving only 3.6% or so for program execution. This is not so! If you look at the next line, you'll see that just about a gig of RAM is being used for buffering/caching. This is basically available memory, since as programs need more RAM, it is reallocated.

So here is the question:

WHAT is consuming all the RAM on your system? Is it Postfix? Email clients? clamav? spamd? Or, is it simply caching a lot, and you're only looking at the first line of the "free" command without looking further?

In other words, dig a little deeper. ps aux will give you some good info on each individual process using RAM, and top will enable you to monitor it in realtime. 99% utilization may not be a problem at all.