Service Dependency Design

[Ethan Galstad]

Hi Marty -

Nagios 3 has improved service dependency check logic, which should solve
any issues you're having with them.  Specifically, read about the
predictive dependency check option:

http://nagios.sourceforge.net/docs/3_0/dependencychecks.html

Marty wrote:
> I am having trouble understanding the design of service dependencies 
> within Nagios.  I thought they could be set up to operate like host 
> dependencies.  For example:
> 
>    Service_A is the master service.
> 
>    Service_B depends on Service_A.
> 
>    If Service_B changes state (say OK to CRITICAL) as a result of its
>    dependency on Service_A, nagios would immediatly follow up with a check
>    of Service_A before sending notifications about B.
> 
> That is how host dependencies work -- you receive a a single alert saying 
> that the router is down rather than about all 50 hosts behind the router.
> However this is not true about service dependencies.
> 
> Within the nagios code (checks.c) it appears that if a service changes 
> state, nagios follows up with a host check, but not a service dependency 
> check.  Nagios only takes the last state of the master service.  If the 
> master service went critical immediately following its check and took down 
> dependent services, notifications could be sent out about all dependent 
> services before nagios gets back to checking the master service again.**
> 
> I want to do the same with service dependencies.  Rather than receiving 
> many alerts about various dependent services, I would like nagios to 
> notify me that the master service is down.
> 
> I want to thank nagios developers for all your hard work.  I would like to 
> contribute back to the group by attempting to add master service checks 
> immediately following state changes of dependent services, however I am 
> likely unaware of all the issues surrounding the design implementation of 
> dependent service checks.
> 
> Is there a particular developer I could contact or a discussion thread 
> about service dependencies and how/why they were implemented as they are 
> in the source?
> 
> Thank you agan for any help you can provide.
> 
> Regards,
> Marty Combs
> 
> 
> 
> ** I can provide a more detailed description of this situation we are 
> having if anyone needs me to.


Ethan Galstad
Nagios Developer
___
Email: nagios at nagios.org
Web:   www.nagios.org

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