[thayne]

It's possible to use http/2 between the load balancer and the app server (haproxy 2.0+ supports this, caddy supports h2, but not h2c). FastCGI has been around longer, and there are probably more reverse proxies that support it on the backend than h2c (or even just h2), but I'm not sure if there are any technical advantages to using FastCGI as the protocol over http/2.

[francislavoie]

Caddy does support h2c actually. It can be enabled on the server https://caddyserver.com/docs/json/apps/http/servers/allow_h2... and at the HTTP proxy module https://caddyserver.com/docs/json/apps/http/servers/routes/h...