Getting Started with Varnish Cache

Chapter 8. Logging, Measuring, and Debugging

Setting up Varnish, configuring parameters, and tuning your VCL is all fun and games, but how do you know how effective your setup is? You could look at the load statistics of your Varnish servers and your backends. If those are fine, you know your environment isn’t on the verge of exploding. Unfortunately, this gives us little information on the hit rate of the cache—it would be nice to identify the hot spots in your application and whether those hot spots are cached appropriately. If it turns out that certain pages aren’t cached when they should be, you would like to know why, right? Who knows, by optimizing your application or your VCL, the load could further drop and this could lead to a downsize of your infrastructure.

Luckily, Varnish offers ways to debug and measure the HTTP requests, the HTTP responses, and the cache. In this chapter, we’ll cover the following tools:

• varnishstat

• varnishlog

• varnishtop

These binaries all use the shared memory log, which we talked about in “Shared log memory storage”.

Note

Varnish offers even more tools, but many are beyond the scope of this book. To learn more, you can have a look at the documentation for binaries like varnishhist and varnishncsa.

Varnishstat

The varnishstat binary displays statistics of a running Varnish instance. These are general statistics about connections, sessions, backends, storage, hit rate, and much more. This is a good dashboard for sysadmins: it shares little ...