VCL reference

Fastly's cache servers run an evolution of Varnish which diverged from the community project at version 2.1. Varnish Configuration Language (VCL) remains the primary way to configure our cache behaviors, and our VCL syntax derives from Varnish 2.1.5, but has been significantly upgraded and extended for Fastly-specific features.

While it's possible that VCL written for the open source Varnish will work on Fastly, our VCL variant should be seen as a separate language. See using VCL for detailed information about the architecture of VCL configurations.