I don't think FastCGI is the way to go. It's old tech we have better systems now.
Usually how high performance sites work is they host the static portion like HTML/JS/CSS/Images on a CDN. While the dynamic server cluster only does REST/GraphQL/WebSocket requests usually on an api.* domain. You use a proxy like Nginx or HAProxy to route between your different dynamic servers in your cluster. Non of it involves CGI.
