Issues with NSCA

Ken Snider ken.snider at datawire.net
Fri Jan 17 00:12:41 CET 2003


Greetings all,

I've witnessed a perplexing issue with NSCA, and was hoping someone my have 
experienced the same, and could perhaps offer a solution to the issue.

We use NSCA to monitor about 350 passive services onto our network. NSCA is 
processed through xinetd -reuse, and has Connections per second (cps) and 
instances set to 200, and UNLIMITED, respectively.

In essence, xinetd will happily accept up to 200 connections per second.

We use a wrapper to massage plugin data and pipe to send_nsca, which in turn 
sends these results to our nagios server. We have about 5 plugin results per 
server, or about 70 servers total doing this, every two minutes.

What this means is, every two minutes, 70 connections are made to NSCA and 
processed.

The *connections* themselves seem to work just fine.. xinetd spawns all the 
required nsca daemons and they seem to communicate well.

The problem, however, is that over time, while nagios will first process all 
these requests without issue, every two minutes, over time, the process 
seems to take longer and longer, until nagios eventually begins tripping our 
freshness threshold, which is set at a more-than-generous 500 seconds.

The box doesn't experience significant load, nor does it seem to be 
network-related. It appears that, for whatever reason, these requests simply 
don't make it into the external command pipe, or they are somehow lost in 
the process.

I'm hoping someone more familiar with the issue than I can explain *what* 
NSCA does, when launched from xinetd, and "likely" blocking on the pipe as 
the requests go into the server.

I'd hope the solution isn't "less passive checks", or "staggered more", 
because that suggests that Nagios won't be able to scale as we grow, and 
we'll reach a point where our passive requests exceed nagios' capability.

-- 
Ken Snider
Senior Systems Administrator
Datawire Communication Networks Inc.



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