Munin is an excellent open source tool for monitoring and graphing server performance metrics. It can be configured to send out alert emails when something goes wrong with your server, and the graphs make it easy to view trends over time: You could see that your site gets much less traffic on a Sunday, for example, or that the number of database queries performed per day has doubled in the last 2 months.

On a Debian-based system installing Munin is as simple as running the following command, and then going to http://your-server/munin/ in your browser:

sudo aptitude install munin

Munin comes with lots of monitoring plugins by default, including those for MySQL, PostgresSQL, Apache, Tomcat, Squid, and for things such a CPU and memory usage, load average, network traffic, and many more. You can also find lots of user submitted plugins on sites like Munin Exchange.

Munin doesn’t have to be used solely for monitoring server performance though. Being so easy to extend Munin is also a great tool for tracking non-server performance related trends over time. In just a few lines of code you could write plugins to track the following stats about your website:

• Number of User signups
• Google PageRank
• Pages in Google’s index
• Number of backlinks
• Number of twitter mentions
• Alexa traffic rank

The number of pages in Google’s index is actually a plugin I’ve written. Simple put the following code in your /etc/munin/plugins directory to see it in action:

#!/bin/sh
# Munin Plugin to display the number of pages in the
# google index for all of the given websites
# Ben Dowling - www.coderholic.com

# Change this to whatever sites you're interested in
websites="www.yahoo.com www.google.com www.twitter.com"

if [ "$1" = "autoconf" ]; then
        echo yes
        exit 0
fi

if [ "$1" = "config" ]; then

        echo 'graph_title Number of Pages in Google Index'
        echo 'graph_args --base 1000 -l 0 '
        echo 'graph_vlabel number of pages'
        echo 'graph_category google'
        echo 'graph_info This graph shows the number of pages in the Google index for a given website.'

        i=0
        for site in $websites
        do
                name="site_${i}"
                echo "${name}.label ${site}"
                echo "${name}.draw LINE2"
                echo "${name}.info The number of pages in the google index."
                i=$((i+1))
        done
        exit 0
fi

i=0
for site in $websites
do
        name="site_${i}"
		value=$(wget -q --user-agent=Firefox -O - "http://www.google.com/search?q=site:${site}" | grep -E "of about [0-9,]+" -o | grep -E "[0-9,]+" -o | sed "s/,//g")
        echo "${name}.value ${value}"

        i=$((i+1))
done

For more details about Munin see their homepage, which also includes detailed documentation on writing your own plugins.

Let me know if you can think of any more Munin plugins that could be interesting, or if you’ve used any yourself!

With the configuration option “log_errors” PHP will log all errors to the Apache error log file, allowing you to see all of the errors that have occurred while people have been using your site. Given the snippet of code below:

<?php
	// Ensure logging is enabled. Ideally this will be set in php.ini
	ini_set('log_errors', 'On');
	// Call a non-existant function to generate an error
	doesNotExist();
?>

You’ll see something like the following entry in the error log, which includes a description of the problem and the file and line number of where the problem occurred:


[Tue May 26 19:54:53 2009] [error] [client 127.0.0.1] PHP Fatal error: Call to undefined function doesNotExist() in /var/www/index.php on line 6


I’ve written a small bash script to mail me all of the PHP errors that it finds in the log. The results are sorted and piped through the “uniq” command to remove any duplicate errors. I’ve set it up to run as a cron task once a day, so if there are ever any problems it isn’t long before I know about them. The code is below:

#!/bin/bash
# Mail out PHP errors that are in the apache error log.
# Note PHP's log_errors must be turned on
# Ben Dowling - www.coderholic.com

errorLog=/var/log/apache2/error.log # Error log location
email=you-email-address@example.com # Send report here

# Pull out the lines that mention PHP, and use AWK to get the column we're interested in
errors=$(cat $errorLog | grep PHP | awk -F'] ' '{print $4}')
# Remove referer information, sort, and remove duplicate entries
errors=$(echo "$errors" | awk -F', referer' '{print $1}' | sort | uniq)
# Check that we actually have some errors
if [ -n "$errors" ]
then
	echo "$errors" | mail "$email" -s "PHP Errors"
fi

If you need to it should be quite easy to modify the script for a slightly different use, such as printing out all the fatal PHP errors that are in the log.

Hope you find it useful!

At work we’re experiencing some fairly rapid growth, and our single production server is starting the feel the strain. I’ve been doing a lot of investigation into how we can scale the site, and thankfully there is lots of information out there.

The “Do you Scale” presentation I saw at PHP London a couple of months ago gave a good high level overview of scalability issues, and included some useful techniques to help you scale.

I think I’ve found the ultimate scalability presentation though: “Real World Web: Performance & Scalability”. The 189 slides contained within this presentation cover almost everything I’ve read elsewhere, and it’s packed full of practice advice!

A question I see asked in lots of places online is how to ensure that a visitor to your site is visiting www.yourdomain.com and not just yourdomain.com. There are lots of good reasons for wanting your visitors to visit the one address rather than both, such as making sure all link and bookmarks count towards the one page, rather than being shared between two.

Some of the solutions I’ve seen have been crazy, like editing every php file on your site to check what the address is, and redirect depending on whether the www is included or not. If you’re using Apache then a very simple solution exists with mod_rewrite. All you need to do is create a .htaccess file in the root directory of your website and add the following lines:

<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTP_HOST} !^www
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]
</IfModule>

Mod_rewrite is very powerful, and allows you to do far more than just add www. to your URLs. If you’re interested in more information then official documentation is a great place to start, and contains lots of examples.