Server Monitoring With munin And monit On CentOS 5.2
In this article I will describe how you can monitor your CentOS 5.2 server with munin and monit. munin produces nifty little graphics about nearly every aspect of your server (load average, memory usage, CPU usage, MySQL throughput, eth0 traffic, etc.) without much configuration, whereas monit checks the availability of services like Apache, MySQL, Postfix and takes the appropriate action such as a restart if it finds a service is not behaving as expected. The combination of the two gives you full monitoring: graphics that lets you recognize current or upcoming problems (like "We need a bigger server soon, our load average is increasing rapidly."), and a watchdog that ensures the availability of the monitored services.
Although munin lets you monitor more than one server, we will only discuss the monitoring of the system where it is installed here.
I want to say first that this is not the only way of setting up such a system. There are many ways of achieving this goal but this is the way I take. I do not issue any guarantee that this will work for you!
1 Preliminary Note
Our system's hostname is server1.example.com, and we have a web site www.example.com on it with the document root /var/www/www.example.com/web.
2 Enable The RPMforge Repository
On CentOS 5.2, munin and monit are not available in the default CentOS repositories. Fortunately we can install them from the RPMforge repository. To enable the RPMforge repository, we run
rpm -Uvh rpmforge-release-0.3.6-1.el5.rf.i386.rpm
rm -f rpmforge-release-0.3.6-1.el5.rf.i386.rpm
on i386 hosts and
rpm -Uvh rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm
rm -f rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm
on x86_64 hosts (please check out https://rpmrepo.org/RPMforge/Using for the latest versions).
3 Install And Configure munin
To install munin on CentOS 5.2, we do this:
yum install munin munin-node
Then we create the system startup links for munin and start it:
chkconfig --levels 235 munin-node on
Next, we must edit the munin configuration file /etc/munin/munin.conf. We want munin to put its output into the directory /var/www/www.example.com/web/monitoring, therefore we change the value of htmldir, and we want it to use the name server1.example.com instead of localhost.localdomain in the HTML output, therefore we replace localhost.localdomain with server1.example.com. Without the comments, the changed file looks like this:
[...] dbdir /var/lib/munin htmldir /var/www/www.example.com/web/monitoring logdir /var/log/munin rundir /var/run/munin # Where to look for the HTML templates tmpldir /etc/munin/templates [...] # a simple host tree [server1.example.com] address 127.0.0.1 use_node_name yes [...]
Next we create the directory /var/www/www.example.com/web/monitoring and change its ownership to the user and group munin, otherwise munin cannot place its output in that directory. Then we restart munin:
mkdir -p /var/www/www.example.com/web/monitoring
chown munin:munin /var/www/www.example.com/web/monitoring
Now wait a few minutes so that munin can produce its first output, and then go to http://www.example.com/monitoring/ in your browser, and you see the first statistics. After a few days this could look like this:
(This is just a small excerpt of the many graphics that munin produces...)
4 Password-Protect The munin Output Directory (Optional)
Now it is a good idea to password-protect the directory /var/www/www.example.com/web/monitoring unless you want everybody to be able to see every little statistic about your server.
To do this, we create an .htaccess file in /var/www/www.example.com/web/monitoring:
AuthType Basic AuthName "Members Only" AuthUserFile /var/www/www.example.com/.htpasswd <limit GET PUT POST> require valid-user </limit>
Then we must create the password file /var/www/www.example.com/.htpasswd. We want to log in with the username admin, so we do this:
htpasswd -c /var/www/www.example.com/.htpasswd admin
Enter a password for admin, and you're done!