Nagios dependency question

[Carroll, Jim P [Contractor]]

Scott Whitney wrote:
> Background:
> a) Nagios runs "here"
> b) There is a router "here"
> c) It goes across the Internet to my coloc site (call it "there")
> d) There is a router "there"
> e) For the purposes of this example, there is 1 "machine" there
> f) "machine" runs httpd
> g) this httpd is shared for all web apps on the box, of which 
> there are 55
> h) I have a script which checks the status of this web app.
> 
> Here's my problem.  When the router, here, is down, I get 59 
> messages.  That
> is, router "here", router "there", machine ping, machine 
> httpd + 55 sites.

Heh.  I'm not aware of a check_sites plugin.  ;-)  How are you actually
checking whether a 'site' is up or down?  (This might be moot, but it might
be useful info.)

> I can solve this using dependencies, but here's my question.

You *can*, but I would recommend you define parents in your hosts.cfg.  Much
gentler on the ol' grey matter.  Read:

http://your_nagios_server/nagios/docs/xodtemplate.html#host

and go straight to the 'parents' directive.  Worth noting:  You don't need
to define *all* the parent nodes in a given hosts config definition.  In
your case, 'router there' would be the parent for all the hosts at the colo,
'router here' would be the parent to 'router there'.  (I'm not entirely
certain how/when you would want to define multiple parents, quite honestly,
but I'm taking the simple approach, and it works quite well.)

> For the dependencies to work properly, each of the sites must 
> be dependent
> on:
>     a) httpd
>     b) ping machine
>     c) ping router "there"
>     d) ping router "here"
> 
> Let's assume I check this every minute.  My math says that 
> this is roughly
> 280 hits on httpd per minute (55 * 5 + 5), 280 pings to the 
> machine per
> minute, 280 pings to the router there per minute and 280 
> pings to the router
> here per minute.

I'm not sure how you arrive at those values.  According to what you've told
us, you have 3 pingable IP addresses, therefore you would get 1 ping per
node per minute.  As for httpd hits, you've so far stated that you have 1
httpd daemon, so we can only extrapolate that only 1 socket is being
listened on.  Perhaps once you've clarified how you define a 'site' and how
you're checking each site, that'll become clearer.  (If you mean that you've
defined 55 IP aliases and you're pinging each one, etc...?)

> This gets a little worse when you realize I actually have 
> over 200 sites,
> not 55.  Also on 7 boxes, not one, so we're looking at more 
> like 1005 per
> minute, spread unevenly across several boxes.

Not quite that bad, given the logic I've been following.

> The question, then, is whether anyone has run into this 
> and/or does Nagios
> take this into consideration via any caching mechanism?  The 
> documentation
> says

Do you mean caching a ping or an httpd check?  That somewhat defeats the
purpose of doing the check to begin with, I'd think, even assuming that you
could do so.

> "Before Nagios executes a service check or sends 
> notifications out for a
> service, it will check to see if the service has any 
> dependencies. If it
> doesn't have any dependencies, the check is executed or the 
> notification is
> sent out as it normally would be. If the service does have one or more
> dependencies, Nagios will check each dependency entry as follows:
> Nagios gets the current status* of the service that is being 
> depended upon.
> "
> 
> * by default this is the current HARD state
> 
> So...from where is it getting this information?  Further 
> perusal through the
> theory section helps me not at all...
> 
> Anyone have ideas on this?

Yes.  Just skip the whole dependancies bit for now, and focus on parents.
Unless you're really really in the mood for visualizing a 4-D Klein bottle.
;)

jc

> Thanks,
> 
> Scott Whitney
> swhitney at Journyx.com
> 
> 
> 
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