Dependent service checks don't fail when depended-on service check fails

Jarrod Moore masternayru at gmail.com
Fri Mar 27 00:20:18 CET 2009


On Thu, Mar 26, 2009 at 7:57 PM, Andreas Ericsson <ae at op5.se> wrote:
> Jarrod Moore wrote:
>>
>> Hello everyone,
>>
>> I have a couple of related questions regarding service dependencies in
>> Nagios and their limitations. I have two service checks (let's call
>> them A and B) and service A depends on service B to function
>> correctly. I want to set Nagios up so that if service B crashes then
>> both services A and B are put into the critical state in Nagios. I've
>> tried using service dependencies in Nagios to represent this behaviour
>> but have yet to be successful. I can only get it to suppress
>> notifications of service A if both services go down.
>>
>
> This is expected behaviour. If A is truly dependant on B, then A will
> turn into a non-ok state of its own volition rather than as a result
> of any dependency magic. Dependencies are designed as a means of
> suppressing notifications. Otherwise, you would *always* get a
> notification for B first, and a minute or so later from A (actually,
> without the dependency you could get from A first).
>
>> Is there a way to do what I'm trying to do here? I'd have thought it
>> would be logical that if a service depends on another service and the
>> service depended on dies then all services depending on it would fail
>> their checks as well, but there;s probably some scenario where it
>> doesn't work so well. I've had a look through the mailing list
>> archives and found someone had asked a similar question to the
>> nagios-devel list about 2.5 years ago and didn't end up getting an
>> answer, so I thought I might ask whether solutions to this type of
>> problem had been developed since then.
>>
>
> They haven't. You're using dependencies the wrong way, really. If
> A is truly dependent on B and doesn't go into a non-ok state after
> B has crashed, then your check isn't doing what it's supposed to do,
> or you've misunderstood the relationship somehow.
>
> If you were to explain what the two services actually are, it would
> be easier to point you to a solution that works.
>
> --
> Andreas Ericsson                   andreas.ericsson at op5.se
> OP5 AB                             www.op5.se
> Tel: +46 8-230225                  Fax: +46 8-230231
>
> Considering the successes of the wars on alcohol, poverty, drugs and
> terror, I think we should give some serious thought to declaring war
> on peace.
>

Well basically I have a map (similar to Google Maps) embedded in a
website, which hits a URL to retrieve maps. So I have one check using
check_http to check that the website itself is up and another check on
that URL to make sure that the map service is available. Now if the
map service goes down, the website is still up but the maps won't
appear, which means the website's functionality is significantly
affected. However, it is still up and viewable so doing a check on the
website URL still passes.

Now of course I could just write a script or something to check both
URLs and set that as the check command. There is a problem for me with
this approach, however, because I have some other instances where a
web service depends on other web services. When I want to use these
services in websites, I'd then have to write a check for each script,
each containing every service in the chain that is needed to display
the website correctly. This way of doing things just seems a bit
repetitive to me, especially when I have a check for these web
services already.

------------------------------------------------------------------------------
_______________________________________________
Nagios-users mailing list
Nagios-users at lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/nagios-users
::: Please include Nagios version, plugin version (-v) and OS when reporting any issue. 
::: Messages without supporting info will risk being sent to /dev/null





More information about the Users mailing list