Re: exim / amavis-ng overload
On Wed, Jul 16, 2003 at 11:26:35AM +0100, Randy Orrison wrote:
> David Fokkema wrote:
> >Many, many mails were downloaded (thanks to this fine group, :-) and
> >almost immediately, my server became irresponsive. I managed to squeeze
> >in and run top which came on after three minutes and saw my load
> >increase from 20 to 30 to 50 to 77.81. I had a few exim processes and
> >_lots_ of amavis processes running. My server started killing processes
> >(out of memory) and I decided to power down (using the button, nothing
> >else worked).
>
> I had a similar problem not long ago after upgrading spamassassin and
> going on holiday.
>
> >1. What can I do when my server overloads like this? Logging in was
> > _very_ difficult or not possible (timeout of 60 seconds on login
> > prompt...)
>
> Not sure about this one, I don't recall what I did in my panic :-(
> Probably killed fetchmail and waited it out.
>
> >2. How do I limit the number of exim processes? Exim is run from inetd
> > and the infopages showed me that smtp_accept_max will not work. Is
> > this indeed a problem? Should I run exim as a separate daemon and
> > enable smtp_accept_max (or keep it at default 20, better than no
> > limit...)? Is every server which runs exim from inetd vulnerable to
> > this (whether deliberate or not) DoS attack?
>
> The solution (which I found after googling around for a while) is to add
> the following settings in your exim.conf file:
>
> # When this option is set, no message deliveries are ever done if the
> # system load average is greater than its value, except for deliveries
> # forced with the -M option. If deliver_queue_load_max is not set and
> # the load gets this high during a queue run, the run is abandoned.
> # There are some operating systems for which Exim cannot determine the
> # load average (see chapter 1); for these this option has no effect.
>
> deliver_load_max = 4
>
> # If the system load average is higher than this value, all incoming
> # messages are queued, and no automatic deliveries are started. If this
> # happens during local or remote SMTP input, all subsequent messages on
> # the same connection are queued. Deliveries will subsequently be
> # performed by queue running processes, unless the load is higher than
> # deliver_load_max.
> # There are some operating systems for which Exim cannot determine the
> # load average (see chapter 1); for these this option has no effect. See
> # also smtp_accept_queue and smtp_load_reserve.
>
> queue_only_load = 4
This seems very nice! Have to try out if amavis is run before or after
queueing (is this a word?) otherwise this won't have effect. If amavis
is run _after_ queueing and before delivery, this is great!
Thanks,
David
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