Fastly VCL reference
Fastly's Varnish is based on Varnish 2.1 and our Varnish syntax is specifically compatible with Varnish 2.1.5. The principal configuration mechanism of Varnish software is the Varnish Configuration Language (VCL), the scripting language used to configure and add logic to Varnish caches. Fastly has included a number of extensions to VCL that won't be covered by any other documentation.
Functions available in Fastly VCL.
VCL variables supported by Fastly.
Fastly's VCL supports variables for storing temporary values during request processing.
Fastly's VCL provides various arithmetic and conditional operators.
Fastly's VCL is a statically typed language. Several types are available.