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load balance

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Victor Duchovni
*nix forums Guru

Joined: 28 Feb 2005
Posts: 2927

Posted: Thu Feb 23, 2006 5:59 pm Post subject: Note

Re: load balance

On Thu, Feb 23, 2006 at 05:40:59PM +0000, Matt Fretwell wrote:

Quote:

On Thu, 23 Feb 2006 08:09:58 -0800
Dennis Peterson <dennispe@inetnw.com> wrote:

For smtp:
I use round-robin dns for load sharing (it can't really
balance the load as it hasn't any idea what load any server
is carrying). You can layer that by using multiple
round-robin mx records, each having equal costs as aol.com has
done.

Round robin on the firewall for each MX IP to several plus
internal servers would also allow the fault tolerance to grow
phenomenally.

I would hazard a guess that the real question the OP tried to ask, but
failed, was how to load-balance the mailstore. That question is not not
a Postfix question, it is about POP, IMAP, storage redundancy, ...

Load-balancing the mailstore is not trivial, a number of approaches are
possible. The simplest is HA NFS + multiple IMAP servers with maildir
that see the same store. I am not sure this scales well to large stores
(much better for POP than IMAP), because the NFS ops to scan large
maildirs can make IMAP performance poor. Otherwise one can look for
file-systems over SAN storage with remote mirroring, HA clusters, ...

Finally, if users never delete email (append-only store), one may be
able rsync (symmetric) the mail between multiple stores. Not sure how
this scales. I have only seen this done for vanity-domain single-user
mail stores.

In any case this question belongs on the Cyrus, Dovecot, Courier-IMAP, ...
mailing lists.

--
Viktor.

Disclaimer: off-list followups get on-list replies or get ignored.
Please do not ignore the "Reply-To" header.

To unsubscribe from the postfix-users list, visit
http://www.postfix.org/lists.html or click the link below:
<mailto:majordomo@postfix.org?body=unsubscribe%20postfix-users>

If my response solves your problem, the best way to thank me is to not
send an "it worked, thanks" follow-up. If you must respond, please put
"It worked, thanks" in the "Subject" so I can delete these quickly.

Matt Fretwell
*nix forums Guru

Joined: 19 Feb 2005
Posts: 583

Posted: Thu Feb 23, 2006 5:40 pm Post subject: Note

Re: load balance

On Thu, 23 Feb 2006 08:09:58 -0800
Dennis Peterson <dennispe@inetnw.com> wrote:

Quote:

For smtp:
I use round-robin dns for load sharing (it can't really
balance the load as it hasn't any idea what load any server
is carrying). You can layer that by using multiple
round-robin mx records, each having equal costs as aol.com has
done.

Round robin on the firewall for each MX IP to several plus
internal servers would also allow the fault tolerance to grow
phenomenally.

Matt

Dennis Peterson
*nix forums beginner

Joined: 22 Feb 2006
Posts: 18

Posted: Thu Feb 23, 2006 4:09 pm Post subject: Note

Re: load balance

Jahidul Hasan wrote:

Quote:

Can anybody give me any idea or document link for load balance of postfix.

I have 3 servers which I need to balance all the mails.

Regards
Jahid

There is both a load sharing and fault tolerant way to do this. Any single
system can fail and the work will continue on the remaining systems.

For spam/virus daemons:

I connect via tcp sockets and use this proxy to load share among several servers:

http://www.inlab.de/balance.html

For smtp:
I use round-robin dns for load sharing (it can't really balance the load as it
hasn't any idea what load any server is carrying). You can layer that by using
multiple round-robin mx records, each having equal costs as aol.com has done.
Notice below that each MX record has 15 for a cost, and that each MX hostname
expands to multiple (round-robin) A records. Four mx records gives them 14 load
sharing mail servers.

$ dig mx aol.com

; <<>> DiG 9.2.4 <<>> mx aol.com

;; QUESTION SECTION:
;aol.com. IN MX

;; ANSWER SECTION:
aol.com. 3600 IN MX 15 mailin-04.mx.aol.com.
aol.com. 3600 IN MX 15 mailin-01.mx.aol.com.
aol.com. 3600 IN MX 15 mailin-02.mx.aol.com.
aol.com. 3600 IN MX 15 mailin-03.mx.aol.com.

;; ADDITIONAL SECTION:
mailin-01.mx.aol.com. 300 IN A 64.12.137.249
mailin-01.mx.aol.com. 300 IN A 205.188.156.185
mailin-01.mx.aol.com. 300 IN A 205.188.158.121
mailin-02.mx.aol.com. 300 IN A 205.188.155.89
mailin-02.mx.aol.com. 300 IN A 205.188.157.25
mailin-02.mx.aol.com. 300 IN A 64.12.138.185
mailin-03.mx.aol.com. 300 IN A 64.12.138.120
mailin-03.mx.aol.com. 300 IN A 205.188.157.217
mailin-03.mx.aol.com. 300 IN A 205.188.159.57
mailin-03.mx.aol.com. 300 IN A 64.12.138.57
mailin-04.mx.aol.com. 300 IN A 205.188.156.249
mailin-04.mx.aol.com. 300 IN A 205.188.159.217
mailin-04.mx.aol.com. 300 IN A 64.12.138.89
mailin-04.mx.aol.com. 300 IN A 64.12.138.152

dp

mouss
*nix forums Guru

Joined: 27 Feb 2005
Posts: 1947

Posted: Thu Feb 23, 2006 2:34 pm Post subject: Note

Re: load balance

Magnus Bäck a écrit :

Quote:

Can you please correct the time on your computer? It's about 60 hours
too fast.

That gives him a DATE_IN_FUTURE_48_96 in SA... but he also gets a
INFO_TLD, and guess why? because of a mailscanner URL!!!
So the scanner gets oneself caught by the underlying filter!

Magnus Bäck
*nix forums Guru

Joined: 26 Feb 2005
Posts: 1366

Posted: Thu Feb 23, 2006 8:23 am Post subject: Note

Re: load balance

On Saturday, February 25, 2006 at 20:53 CET,
Jahidul Hasan <jahid@bjitbd.com> wrote:

Quote:

Can anybody give me any idea or document link for load balance of
postfix.

I have 3 servers which I need to balance all the mails.

For incoming mail, three equal-priority MX records in DNS will balance
the load reasonably well.

Can you please correct the time on your computer? It's about 60 hours
too fast.

--
Magnus Bäck
magnus@dsek.lth.se

MD. Jahidul Hasan
*nix forums addict

Joined: 28 Feb 2005
Posts: 51

Posted: Thu Feb 23, 2006 8:23 am Post subject: load balance

Can anybody give me any idea or document link for load balance of postfix. I have 3 servers which I need to balance all the mails. Regards Jahid -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.

Google

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