Varnish Cache

What Varnish Cache is

Varnish Cache is a free, self-hosted reverse caching proxy for Linux. It serves saved responses from memory and forwards other requests to origin servers. Its caching rules are written in Varnish Configuration Language (VCL), which compiles to native code. Cached items follow standard HTTP cache headers and leave the cache when they expire. Varnish supports TLS termination within the process and TLS connections to dynamic origin backends. The project provides container images and a Kubernetes Helm chart, plus installation guidance for Debian, Ubuntu, Red Hat Enterprise Linux and compatible distributions. For monitoring, varnishlog provides structured logs and varnishstat provides metrics. Varnish modules add functions that can be called from VCL. The security guide describes controls at the command line, CLI, VCL and HTTP request levels. One consideration is that Varnish avoids caching when it cannot determine that it is safe; applications may need configuration changes to achieve a high cache hit rate. The project identifies supported releases and marks unlisted releases as end-of-life and unsupported.