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.

The Fastly CDN outage on June 8th, which took down a major part of the internet, including popular websites and services, such as Reddit, Spotify, Twitch, Stack Overflow, GitHub, gov.uk, Hulu, HBO Max, Quora, PayPal, Vimeo, Shopify, Stripe, and news outlets CNN, The Guardian, The New York Times, BBC and Financial Times, taught everyone four important things: