actix-web/guide/src/qs_13.md

HTTP/2.0

Actix web automatically upgrades connection to HTTP/2.0 if possible.

Negotiation

HTTP/2.0 protocol over tls without prior knowledge requires tls alpn. At the moment only rust-openssl has support. Turn on the alpn feature to enable alpn negotiation. With enabled alpn feature HttpServer provides the serve_tls method.

[dependencies]
actix-web = { version = "0.3.3", features=["alpn"] }
openssl = { version="0.10", features = ["v110"] }

use std::fs::File;
use actix_web::*;
use openssl::ssl::{SslMethod, SslAcceptor, SslFiletype};

fn main() {
    // load ssl keys
    let mut builder = SslAcceptor::mozilla_intermediate(SslMethod::tls()).unwrap();
    builder.set_private_key_file("key.pem", SslFiletype::PEM).unwrap();
    builder.set_certificate_chain_file("cert.pem").unwrap();

    HttpServer::new(
        || App::new()
            .resource("/index.html", |r| r.f(index)))
        .bind("127.0.0.1:8080").unwrap();
        .serve_ssl(builder).unwrap();
}

Upgrade to HTTP/2.0 schema described in rfc section 3.2 is not supported. Starting HTTP/2 with prior knowledge is supported for both clear text connection and tls connection. rfc section 3.4

Please check example for a concrete example.