Recently, Varnish Technical Evangelist Thijs Feryn led a webinar covering Varnish Configuration Language (VCL), the unique programming language that powers all of our software, as well as the popular open source Varnish Cache. For those who weren’t able to attend the webinar, you can watch it here.  

Fastly VCL is a domain-specific programming language which has evolved from the Varnish proxy cache, which is part of Fastly's platform architecture. Varnish Enterprise VCL, instead, is specific to the Varnish Software solutions. There are some architectural similarities between Varnish Cache open source, Fastly and Varnish Enterprise, but as it is said, the devil’s in the details, hence this blog post.

This week’s episode of Two Minute Tech Tuesday explains how the built-in Varnish Configuration Language (VCL) works. The built-in VCL is VCL code that is executed by default, even if you don't write any VCL yourself.

This week’s episode is about Grace mode, Varnish’s interpretation of stale-while-revalidate.