Scaling nagios: The right way to go?

[Andreas Ericsson]

Rob Moss wrote:
> Hi,
>    AOL UK is using Nagios 2.0b3 for some monitoring (under 1,000 hosts).
> 
> I'm actively developing plugins and tuning/compiling code for Sun 
> Solaris 8 and 9, no problems so far.
> 
> There are some real bottlenecks performing monitoring from one host, 
> aside from the fact that some of the built-in plugins are simply 
> wrappers to the real program (check_icmp for a start).
> 

check_icmp is not a wrapper. It was written for the precise purpose of 
getting rid of the extra overhead caused by invoking an external program 
(and to get rid of the umpteen-hundred people telling the list that it 
doesn't work on Fedora Core 3).

> If you are after performance, multiple check hosts feeding into a 
> collector is probably the best way,

Using check_icmp in check_host mode will easily cut the performance loss 
of services going to non-OK states by a rough 99%, although that only 
works when the host is up. When it's down, it's more like 50%.

> and scrapping some of the built-in 
> nagios checks,

Nagios has no built-in checks. It wasn't designed for it, and benchmarks 
show that it would hardly benefit at all from it. This has been 
discussed and tested in great detail on the nagios-devel@ mailing-list.

> in favour of compiled C checks that do all the work 
> instead of being wrappers around other system tools.
> 
> Also, the built-in Perl compiler should be quite fast for executing Perl 
> scripts, such as HTTPS checks in perl/LWP etc.
> 

Compiled C-programs run about 30% faster than cached perl-plugins 
executed by the embedded perl interpreter. I believe some of that has to 
do with exception handling in Nagios when the EPN is compiled in 
(theoretically it should only be about a 10% loss due to perl creating 
less efficient machine code than gcc), but I haven't done any profiling 
on it, so I can't say for sure.

-- 
Andreas Ericsson                   andreas.ericsson at op5.se
OP5 AB                             www.op5.se
Lead Developer


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