When used together, these graphs give us quick feedback on what sort of errors are occurring on our site and whether they are likely to be related to a recent code promotion, or are the effect of some other condition (bad hardware, third-party APIs failing, SEM gone awry, etc.).

I figured someone might find these useful, so I’m posting the code for both Munin plugins.

Code Uptime

When we deploy code to our servers, we add a timestamp file that is used to manage versioning of deployments to make things like rolling back super easy.  It’s also handy for measuring how long it’s been since the last deployment.  All this plugin does is reads how long ago that file was modified.

We run multiple applications on the same clusters of servers. I wrote our code deployment process in a manner that allows for independent deployment of each application. For example, one team working on our Facebook apps can safely deploy code without interfering with the deployment schedule another team is using for new features that will be released on the CafeMom web site.

Each of these applications is deployed to a separate directory under a root, let’s say “/var/www.”  This explains why the plugin is reading a list of files (directories) under APPS_ROOT.  Each app has it’s own reported uptime on the Munin graph.

#!/bin/sh
#
# Munin plugin to monitor the relative uptime of each app
# running on the server.
#

APPS_ROOT="/var/www/"

# Cap the uptime at one day so as to maintain readable scale
MAX_MIN=1440

# Configure list of apps
if [ "$1" = "config" ]; then
 echo 'graph_title Application uptimes'
 echo "graph_args --base 1000 --lower-limit 0 --upper-limit $MAX_MIN"
 echo 'graph_scale no'
 echo 'graph_category Applications'
 echo 'graph_info Monitors when each app was last deployed to the server.'
 echo 'graph_vlabel Minutes since last code push (max 1 day)'

 for file in `ls $APPS_ROOT`; do
 echo "$file.label $file"
 done
 exit 0
fi

# Fetch release times
now_sec=`date +%s`

for file in `ls $APPS_ROOT`; do
 release_sec=`date +%s  -r $APPS_ROOT/$file/prod/release_timestamp`
 diff_sec=$(( $now_sec - $release_sec ))
 diff_min=$(( $diff_sec/60 ))
 ((diff_min>MAX_MIN?diff_min=MAX_MIN:diff_min))
 echo "$file.value $diff_min"
done

Error Logs

The second plugin uses grep to search for occurrences of specific error-related strings in our log files. In our case, the graph period was set to “minute” because that gives the best scale for us (thankfully, it’s not in errors per second!).

If you’re wondering about using grep five times against large error files every time Munin runs (every five minutes), I want to point out that we rotate our logs frequently which ensures that these calls are manageable. If you run this against very large error logs you may find gaps in your Munin graphs if the poller times out waiting for the plugin to return data points.

Even if you don’t care about PHP logs, you may find this to be a simple example of using Munin to examine any sort of log files that your application is creating.

#!/bin/bash

#
# Collect stats for the contents of PHP error logs. Measures notice,
# warning, fatal, and parse level errors, as well as custom errors
# thrown from our DB connection class.
#

logs="/var/log/httpd/*.error.log"

# CONFIG

if [ "$#" -eq "1" ] && [ "$1" = "config" ]; then
	echo "graph_title Error Logs"
	echo "graph_category applications"
	echo "graph_info Data is pooled from all PHP error logs."
	echo "graph_vlabel entries per minute"
	echo "graph_period minute"
	echo "notice.label PHP Notice"
	echo "notice.type DERIVE"
	echo "notice.min 0"
	echo "notice.draw AREA"
	echo "warning.label PHP Warning"
	echo "warning.type DERIVE"
	echo "warning.min 0"
	echo "warning.draw STACK"
	echo "fatal.label PHP Fatal"
	echo "fatal.type DERIVE"
	echo "fatal.min 0"
	echo "fatal.draw STACK"
	echo "parse.label PHP Parse"
	echo "parse.type DERIVE"
	echo "parse.min 0"
	echo "parse.draw STACK"
	echo "db.label DB Error"
	echo "db.type DERIVE"
	echo "db.min 0"
	echo "db.draw STACK"
	exit
fi

# DATA

# The perl code at the end of each line takes a list of integers (counts) from grep (one per line)
# and outputs the sum.

echo "notice.value `grep --count \"PHP Notice\" $logs | cut -d':' -f2 | perl -lne ' $x += $_; END { print $x; } ' `"
echo "warning.value `grep --count \"PHP Warning\" $logs | cut -d':' -f2 | perl -lne ' $x += $_; END { print $x; } ' `"
echo "fatal.value `grep --count \"PHP Fatal error\" $logs | cut -d':' -f2 | perl -lne ' $x += $_; END { print $x; } ' `"
echo "parse.value `grep --count \"PHP Parse error\" $logs | cut -d':' -f2 | perl -lne ' $x += $_; END { print $x; } ' `"
echo "db.value `grep --count \"DB Error\" $logs | cut -d':' -f2 | perl -lne ' $x += $_; END { print $x; } ' `"

I’m open to comments and suggestions on how we use these, or how they were written.  Spout off below.