FAQ: Passive host checks?

[Jason Marshall]

> I am investigating the possibility of adding passive host checks in 
> 2.0.  However, allowing passive checks opens a whole new can of worms 
> as far as host check logic is concerned.  For instance, if a host is 
> reported (passively) as being down (it was previously up), what 
> should happen with child hosts?  Should those be actively checked 
> according to the current tree traversal logic?  Also, host checks are 
> performed on-demand only (synchronously), so how do you handle 
> asynchronous results?  Host checks also get priority over pending 
> passive service check results, so that has to be figured out.

If a passive  host check reports that a host is down, you _have_ to assume
that the script knows what it's doing.  If the host check is stale, then I
think the child hosts need to be checked independently, and probably
actively.

To me, the entire point of using passive host checks would be nullified if
the children were checked despite the parent host being down, rightly or
wrongly.  

The passive host checking script would have to go to some length to ensure
that the host really was down, however.

> Anyway, it isn't exactly trivial without changing a good portion of 
> how the host check logic works.  I'll be looking into it though...

That's what I figured, after seeing how passive checks were integrated
into the service-checking logic.  It's not a one-liner, by any means!

> 
> On 2 Oct 2002 at 8:52, Jason Marshall wrote:
> 
> > > Passive *service* checks are well documented; passive *host* checks
> > > are not.
> > 
> > There are no passive host checks.  I tried that already, and it always
> > uses the active method, and ignores passive updates (which are, granted,
> > documented as service check updates).
> > 
> > I, too, would like a way to monitor hosts that isn't based on Nagios's
> > large-grain checking granularity.  I can tell within 2 seconds if a router
> > that lots of other hosts are dependent upon are down -- I don't want the
> > remote hosts being checked for up to a full minute (and failing, thereby
> > alerting me) when it's really the router that'd down.  If I could tell
> > nagios (passively) within 2 seconds of the incident that the router is
> > down, I'd avoid a lot of spurious alerts...
> > 
> > > My current workaround is to define a service called ALIVE and
> > > report passive service checks for that service, but that is not
> > > 100% satisfying.
> > 
> > I agree.  I haven't looked at the part of the code that would make passive
> > host checks possible, but it seems like it could be a major undertaking...
> > And there could be underlying reasons why such a check would be a bad
> > thing...
> > 
> > ---
> > Jason Marshall, Unix Geek, Kelman Technologies, Inc., Calgary, AB, Canada.
> > 
> >   From a Sun Microsystems bug report (#4102680):
> >     "Workaround: don't pound on the mouse like a wild monkey."
> > 
> >   "I have great faith in fools: 
> >      Self confidence my friends call it."  -Edgar Allan Poe
> > 
> > 
> > 
> > 
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> 
> 
> 
> Ethan Galstad,
> Nagios Developer
> ---
> Email: nagios at nagios.org
> Website: http://www.nagios.org
> 
> 
> 
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---
Jason Marshall, Unix Geek, Kelman Technologies, Inc., Calgary, AB, Canada.

  From a Sun Microsystems bug report (#4102680):
    "Workaround: don't pound on the mouse like a wild monkey."

  "I have great faith in fools: 
     Self confidence my friends call it."  -Edgar Allan Poe




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