Varnish and VCL were the hotness at the time Fastly was coming up so it sort of makes sense, but Varnish also doesn’t support WebSockets, can’t proxy GRPC, etc so they’re very limited in functionality vs CloudFlare.
I doubt they’d build it on Varnish today, but it’s a bit late now since they allow custom VCL (which has now proven to be a terrible idea) and will have to support that for eternity.
They can run two or more serving stacks side by side though if it comes to that.
And to add to your point, they also have a separate process that speaks QUIC. It’s an interesting tech stack with a lot of technical debt.
I doubt they’d build it on Varnish today, but it’s a bit late now since they allow custom VCL (which has now proven to be a terrible idea) and will have to support that for eternity.
They can run two or more serving stacks side by side though if it comes to that.
And to add to your point, they also have a separate process that speaks QUIC. It’s an interesting tech stack with a lot of technical debt.