Nagios behaviour when scheduling checks

[Sean McAfee]

Mohr James wrote:
> Hi All!
>
> We are running Nagios 3.0.1 and have serveral services with a check
> interval of 5 Minutes and retry of 1 minute. The problem is that the
> checks have a timeout of 65 seconds. I looked through the documentation
> but couldn't find out how Nagios behaves in this case.
Simple answer: the clock doesn't start until the first check exits

Real answer:
Since retry_interval is only used on an non-OK return, Nagios must 
process the prior check before it can tell if it needs a retry.  

The documentation is from 2.x since 3.x is "coming soon", but look at 
http://nagios.sourceforge.net/docs/2_0/images/checktiming.png (taken 
from http://nagios.sourceforge.net/docs/2_0/checkscheduling.html). 

- The X3 service reaper event is the one that pulls the result of a check
- X4/E is just the next check and not necessarily the next "normal" check. 
- If X3 is OK, then X4 is calculated from normal_check_interval
- If X3 gets a non-OK,  it would evaluate $SERVICEATTEMPT$ and 
$MAXSERVICEATTEMPTS$ to determine $SERVICESTATETYPE$, which then 
dictates whether the daemon needs to reschedule using retry_interval vs. 
normal_check_interval (and whether you've transitioned, which would kick 
off notifies, etc...)

In your situation:
1. Check 1 kicks off at 12:00:00 & times out at 12:01:05.
2. Nagios sees that it needs to retry_interval because 
$MAXSERVICEATTEMPTS$ > $SERVICEATTEMPT$
3. Check 2 is scheduled for 12:02:05 & times out at 12:02:10
4. Nagios sees that $MAXSERVICEATTEMPTS$ = $SERVICEATTEMPT$ and 
transistions $SERVICESTATETYPE$ from SOFT to HARD


If you were to set max_check_attempts to 3, the only difference would be:
4. Nagios sees that it needs to retry_interval because 
$MAXSERVICEATTEMPTS$ > $SERVICEATTEMPT$
5. Check 3 is scheduled for 12:03:15 & times out at 12:04:20
6. Nagios sees that $MAXSERVICEATTEMPTS$ = $SERVICEATTEMPT$ and 
transistions $SERVICESTATETYPE$ from SOFT to HARD

-- 
Sean McAfee
System Engineer

Collaborative Fusion, Inc.
 smcafee at collaborativefusion.com
 412-422-3463 x 4025

5849 Forbes Avenue
Pittsburgh, PA 15217

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