Another push I’ve been working on for a few years now is comprehensive monitoring of our systems. When I started at my job, monitoring was being done through a home-grown script, that would run once an hour. While not particularly bad, it had some major shortcomings. Primarily, the hour lag time meant that, if a problem occurred shortly after the script ran, you wouldn’t know about it for nearly an hour. Another problem was that, while the script would make note of system problems, the only notification mechanism was “someone needs to visit the web page it generates”. During a normal workday, that might be OK, but evenings and weekends? So, at least for my benefit, I set up a monitoring system that could not only monitor systems more frequently, but monitor more systems, and send out alerts via email, cell phones, etc.

For reasons I won’t get into here, what I chose to use for configuration management was Puppet, and I’d already chosen Nagios as my monitoring system. So far, my biggest problem with Nagios has been finding the time to add new systems to it, figuring out what services to check, etc. It’s not a particularly difficult thing to do, but in the grand scheme of things, it was just something that always fell by the wayside in the drive to get more systems set up, deal with user problems, and put out the inevitable fires. That is, until recently.

My original Nagios install was done on an aging box that has been serving as a development web server for our group. I did the install shortly after I’d started, so had I been around longer, I might have either waited, put in a request for new hardware, or found a way to get virtualization into our environment sooner. Overall, it worked, but it was in general a pain dealing with the box, a RHEL3 server, since it was so far out of date. Recently, I’ve set up a VM on our XenServer cluster to be our new Nagios box. Since I’ve also been playing with Puppet, I wanted to automate things as much as possible, since every new system created should be managed by Puppet (though reality slightly differs from that).

Fortunately, the groundwork for automating Nagios monitoring with Puppet is already built in to Puppet. It took me a little bit to wrap my head around the concepts, but the example helped and served as a base.

Now, even though I’m still in the process of setting things up, I’ve gotten to the point where my new Nagios server is already monitoring about 30% more information about hosts (422 services vs 308 on the old server), even though the number of hosts is currently about half (48 hosts vs 99 on the old). All of it done automatically, and here’s how.

First, set up stored configurations on your puppetmaster. You’ll need to specify a database in which to store your puppet-collected facts and resources. While the default is SQLite, I ran into problems with concurrent access. Since I’m also currently responsible for the handful of MySQL servers we have, I decided to just use one of those. Create a database and user for puppet to use, then tell the puppetmaster about it. Your [puppetmasterd] section of puppet.conf should look something like this when you’re done:

Your paths may likely be different than mine. If your DB server is running on the same host as the puppetmasterd process, dbserver should be “localhost”, and you’d uncomment and adjust the path of the dbsocket line. The downcasefacts line is set to “true” so that I can make use of the $operatingsystem fact later on without having to muck with changing the case later.

Next, you’ll want to create a nagios module in Puppet. The Exported Resource example linked above served as my template, but I’ve made a few changes to it. My puppet/modules/nagios/manifests/init.pp file currently looks like this:

To use it, I simply do an include nagios in the node definition for my Nagios server in puppet, and in my basenode node definition, I’ve done an include nagios::target. Each of the @@ lines will collect information for each machine managed by puppet that inherits from basenode. The “collect resources and populate /etc/nagios/nagios_*.cfg” portion is the real magic, however. Each of those lines will cause puppet to collect all the matching resources, and output them to files in /etc/nagios. The only real caveat, which I also noticed in the example I built upon, is that I’m having trouble convincing puppet to reload nagios when the files are updated, which I just brute-force solved with a periodic cronjob to run nagios’ init script with “reload”.

I’m also slowly adding nagios entries for each service that puppet manages in some form. Currently, that means things like apache and ssh. For example, in my apache2 module’s init.pp, I have the following in my class:

This both monitors over-the-wire connections to port 80 on webservers, via the check-http command, but also monitors the number of httpd processes running on each host, via remote-nrpe-httpd-procs.

Similarly, for ssh, I have:

to monitor whether sshd is accepting connections on my systems.

And that, basically, is how I’m automatically monitoring all puppet-managed hosts in my environment. Whenever I set up a new host, I activate puppet on the host to ensure configurations I care about are synced to my master templates, and now as a bonus, puppet automatically tells nagios to start monitoring the services it knows about on the host. By expending a little extra effort once now, I’ve managed to be lazy later on multiple times over, truly something a Systems Administrator should be doing!