When to use passive vs. active checks?

[Greg Vickers]

Hi Josh,

Josh Endries wrote:
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> Hello,
> 
> I'm reinstalling my Nagios server with v2.0 and it's going well so
> far, but I'm curious why people use passive vs. active checks? I
> thought about it while setting up check_disk and _load etc., which
> are currently active, but seem like that may be better suited to be
> passive checks, since they're "internal", that is they don't provide
> a network service that needs to be connected to, I guess.

We use passive checks here to get startup/logon/logoff(reboot) 
information from our lab hosts - a group policy is run at these times 
and that runs send_nsca compiled under Cygwin in the Win32 environment. 
At the time, this was the easiest/best way of getting this information.

I haven't used passive checks in any other situations, but the manual 
states usages like getting information from a severely firewalled host, 
for example.

> I know the guide says passive checks are for sporadic things, and
> really it could be almost anything, but does anyone follow guidelines
> or anything? I figure performance would be saved by making them
> passive, maybe this is a usual way of setting these sorts of tests up?

Passive checks can be used for just about anything, if you really 
want/need to. When setting up a passive check, some trigger has to run a 
script or executable that will send information to the Nagios server, 
rather than the Nagios server actively scheduling a check of a service 
and starting a process to get that information.

Performance on the Nagios host can be saved, for example if a plugin 
used a large amount of CPU to process results before sending the 
information back to Nagios, you could move this processing overhead to 
another host. But you don't avoid having to do the processing, you just 
move it somewhere else :)

Food for thought.

HTH,
-- 
Greg Vickers
Project Manager, IT Security
Information Technology Services
Queensland University of Technology
L12, 126 Margaret St, Brisbane

Phone: (07) 3864 9536
Email: g.vickers at qut.edu.au
IT Security web site: http://www.its.qut.edu.au/itsecurity/

CRICOS No. 00213J


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