Varnish is a high performance HTTP Cache and provides incredible performance for sites and applications. Server Density is a hosted server monitoring application, which deals with reporting, managing and alerting you to any server issues. Server Density has support metrics such as Apache, Nginx, MySQL but not Varnish.
Varnish support isn’t provided by default, so here’s a Server Density Varnish plugin which will provide loverly looking graphs like:
Usage
Usage gives you a good breakdown of cache hits vs cache misses.
Cache Percentage
Cache Percentage is a pretty important metric, the higher the value the more performance you’ll get out of Varnish.
Backends
Gives you a good breakdown of how you backends, import metrics to notice are backend_busy and backend_fail
Total Bytes
It’s probably the least useful day to day, but can let you know if you’ve just served a surge of traffic.
With any of these graphs, Server Density allows you to set alerts for any important metrics.
Installing the plugin is fairly straightforward, Varnish needs to be running with the management port enabled next you’ll just need to edit the plugin to provide the port and IP address, next you’ll need to setup the graph groups from within SD. Unfortunately there isn’t any way to preload a plugin with graphs or provide configuration options.
If you’ve got some improvements to make, please fork the plugin and send me a pull request.