Hi
This is a rather long support request, for that I am sorry. Any help or
clarification would be help
full.
Background:
-----------
I am currently in a discussion with my managed dedicated server service
provider about making
performance related changes to the Exim setup.
I have very limited access to the server and can't see all the config files so
what I have learnt is
through trail and error and with the assistance of the support department of my
hosting company.
As I am just a client to keep things clean I will not be naming the hosting
company. I have a good
relationship with them and I would like to keep it that way.
The Problem:
------------
The problem we have been having is that our server has these major spikes a few
times a day where
load goes through the roof and other services IE: LAMP struggle and start to
timeout.
Their dedicate server setup uses Puppet to manage all their managed dedicated
servers and us as the
clients are allowed to request limited changes through the uses of extra
customization settings
files that is not managed by Puppet that overrides or extends the current
settings.
I have successfully made lots of customizations to PHP and mySQL using these
same customizations
files.
All servers run Debian and I think the default Debian Exim config files. If
there are
changes/customization of the default packaged Debian Exim config files my
understanding is that they
are minor.
My suggested changed:
---------------------
Based on my limited investigation I have found the load spikes seem to coincide
with a spike in the
number of Exim process. Normally there would be between 1-5 Exim process
running and load will be
low. Then the load spikes there would be between 10-50 Exim processes and then
the load would jump
to 10-90. This would last for a few min at most 5-8min and then drop quickly
and load and
responsiveness would normalize.
My requested changes based on my reading of the Docs are the following.
remote_max_parallel = 1
queue_smtp_domains = *
My understanding is that this should reduce the number of process started for
remote deliveries and
should mitigate these spikes by preventing immediate delivery for remote SMTP
hosts.
Maybe later if needed, I might consider reducing queue_run_max.
Support Admin feedback:
-----------------------
The problem is when I requested to add the queue_smtp_domains setting to the
customizations file I
got the following response from the support admin's.
> When trying to add the last customisation, Exim4 failed to restart the
> process saying that
> 'queue_smtp_domains' as already been defined in the main config.
>
> The current setting is:
> queue_smtp_domains = +etrn_domains
After additional investigation I have sort of worked out but can't be 100% sure
that they have some
of the following settings set in the main config file.
domainlist etrn_domains = lsearch;/etc/exim/domains.etrn
domainlist our_domains = +local_domains :\
+virtual_domains :\
+vmail_domains :\
+uucp_domains :\
+smart_route_domains :\
+etrn_domains
queue_smtp_domains = +etrn_domains
queue_domains = +etrn_domains
hold_domains = +etrn_domains
My understanding is that the setting hold_domains is not compatible with
queue_domains or
queue_smtp_domains. So I can't request for "*" to be added to the domains.etrn
file as this would
affect other settings as well.
I later also got the following response from them.
> You are correct, domains.etrn file that will get checked for additional
> settings.
>
> However this file is always empty unless you specify differently. This empty
> file acts the same
> as the '*' according to our administrators.
>
> 'hold_domains' is also set to this empty file and will have no impact on mail
> delivery at the
> moment.
I believe the second line of the above response to be wrong or some sort of
misunderstanding between
me, support and the admin's.
My Questions:
-------------
So my question is what I can propose they change. A change to a Puppet managed
config file is
something that requires major approval and to be rolled out to all their
servers for consistency.
Am I able to maybe set the request change in the customizations file in a way
to overrides or
extends this setting and get Exim to successfully restart without changing the
main config file that
is managed by Puppet?
I believe their setup is incorrect and you would never set queue_smtp_domains
and queue_domains and
hold_domains to the same domainlist file. Is my understanding wrong or right?
If this is how the default Debian package is configured and if it is
technically incorrect I am a
little shocked.
Any help or clarification would be greatly appreciated.
Justin
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