Nagios deployment planning

[Thomas Guyot-Sionnest]

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On 23/02/09 06:32 AM, Alex Dehaini wrote:
> Alot of things count when deploying nagios. Take for instance - if you
> run your service check every 5 minutes, it is not the same when you run
> it every 30 seconds.
> 
> So, throw some more light and we might be able to help. I run about 1000
> services with 300 hosts. I use a P4 2.0 Ghz with 2 gb of ram. So far,
> nagios can take the load. I check services every 90 seconds.

It also depends on the type of checks you're doing. Plain C plugins runs
very well; Perl plugins, even with ePN, require much more CPU cycles to run.

I have an old server running nearly 1600 checks per minute on a 1.4Ghz
PIII while another one, dual Xeon 2.4Ghz, run a little bit hotter with ~
1300 checks per minute just because a bigger portion of them are Perl
checks (all running under ePN).

There's also the fact that ePN leaks memory (the rate depends a lot on
the slecific plugins/modules running) and cause load to grow higher as
time goes. Without ePN is much worse though - my dual-Xeon wouldn't keep
up without it.

Another consideration is 32 vs 64 bit. Since Nagios forks a lot, the
process size has a noticeable influence on system load, and by making
pointers twice as big, 64bit make processes larger as well. On a 64bit
system it may be worth comparing Nagios speed when compiled in 32bit (if
your system doesn't have a 32bit-capable compiler, compile it on a 32bit
system and copy it over). Don't forget to compile the plugins in 32bit
as too - ePN would need a 32bit Perl installation (or at lease
libraries) as well...

Finally, I don't think a virtual machine is the best choice for nagios,
again the amount of forks makes a good proportion of the system load
from kernel calls. Kernel-mode in emulated in virtual machines which
make it slower.

You can always test with check_dummy and check_stuff.pl (in
Nagios::Plugin source distribution). Create a lot of hosts and services
and see how load is affected.


- --
Thomas
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