Monitoring Varnish with Munin
Varnish is a great reverse proxy and very useful for load balancing. Here you can find a tutorial on installing Varnish: Installing and configuring Varnish HTTP accelerator.
Munin is a network/system monitoring application that presents output in graphs through a web interface. If you haven't installed it already, use this tutorial: Monitoring multiple servers with Munin.
Assuming you have both varnish and munin installed, here's a tutorial on installing a plugin for munin to monitor Varnish.
1. Install git-core to receive the plugin from github
apt-get install git-core
Monitoring multiple servers with Munin
Munin is a network/system monitoring application that presents output in graphs through a web interface. Its emphasis is on simple plug and play capabilities. A large number of monitoring plugins are available. Using Munin you can easily monitor the performance of your computers, networks, SANs, and quite possibly applications as well. It makes it easy to determine "what's different today" when a performance problem crops up. It makes it easy to see how you're doing capacity wise on all limited resources.
Master monitoring server
1. Install Munin and Munin node daemon:
apt-get install munin munin-node