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layout: post
title: "Monitoring Apache with Bluepill"
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p(meta). 22 December 2009

I always used "god":http://god.rubyforge.org/ to monitor my processes. god is working fine, has a lot of features and is very easy to use, but has some serious "memory":http://groups.google.com/group/god-rb/browse_thread/thread/1cca2b7c4a581c2/69f69f602add7636?lnk=gst&q=memory+leak#69f69f602add7636 leaks. To handle this problem I usually set-up a cron to restart god every day.

Recently I read an "article":http://asemanfar.com/Why-We-Wrote-Bluepill about a new process monitoring tool called "bluepill":http://github.com/arya/bluepill based on EventMachine. The DSL looks simple and comes memory-leaks-less.

In this article I'll cover how to install it and monitor apache.

First let's grab it :

{% highlight bash %}
sudo gem install bluepill
{% endhighlight %}

Next, we need to configure the syslogger to log the local6 facility used by bluepill.

If your syslogger is syslog, add a line to __/etc/syslog.conf__ :

{% highlight bash %}
local6.*          /var/log/bluepill.log
{% endhighlight %}

If it's syslog-ng, add ths to __/etc/syslog-ng.conf__ :

{% highlight bash %}
filter f_local6 { facility(local6); };
destination d_local6 { file("/var/log/bluepill.log"); };

log { source(src); filter(f_local6); destination(d_local6); };
{% endhighlight %}

You'll also want to add __/var/log/bluepill.log__ to __/etc/logrotate.d/syslog__ so that it gets rotated.

Next restart your syslogger, for syslog-ng :

{% highlight bash %}
sudo /etc/rc.d/syslog-ng restart
{% endhighlight %}

And finally create the __/var/bluepill__ directory for bluepill to store its pid and sock files.

Finally let's create our bluepill script to monitor apache in __apache-monitor.pill__ :

{% highlight ruby %}
Bluepill.application("httpd") do |app|
	app.process("httpd") do |process|
		process.pid_file = "/var/run/httpd/httpd.pid"
		process.start_command = "apachectl start"
		process.stop_command = "apachectl stop"
		process.restart_command = "apachectl restart"
		process.start_grace_time = 10.seconds
		process.stop_grace_time = 10.seconds
		process.restart_grace_time = 10.seconds
	end
end
{% endhighlight %}

This simple script just checks if apache is up and if not reboot it.
You can try it by :

{% highlight bash %}
sudo bluepill load apache-monitor.pill
{% endhighlight %}

You can try to kill your httpd processes and you'll see the magic happens, bluepill will restart them.

Bluepill comes with some great features to monitor your memory and cpu, so you can add to your script :

{% highlight ruby %}
process.checks :cpu_usage, :every => 10.seconds, :below => 5, :times => 3
process.checks :mem_usage, :every => 10.seconds, :below => 100.megabytes, :times => [3,5]
{% endhighlight %}

The first line checks every 10 seconds to make sure the cpu usage of this process is below 5 percent; 3 failed checks results in a restart. 
The second line checks every 10 seconds to make sure memory usage is below 100MB; 3 out of 5 failed attempts results in a restart.

If you want your bluepill daemon to run at boot, just add a line to __/etc/rc.local__ :

{% highlight bash %}
sudo bluepill load /full/path/to/your/script/apache-monitor.pill
{% endhighlight %}