http2 server can't send the Header [Upgrade] to backend

[pigeon1990@…]

My server use the http2 protocol, and the client sends websocket requests, but the [Upgrade]Header cannot be forwarded to the backend server.

#user  nobody;
worker_processes  1;

#error_log  logs/error.log;
#error_log  logs/error.log  notice;
#error_log  logs/error.log  info;

#pid        logs/nginx.pid;


events {
	worker_connections  1024;
}


http {
	include       mime.types;
	default_type  application/octet-stream;

#log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
#                  '$status $body_bytes_sent "$http_referer" '
#                  '"$http_user_agent" "$http_x_forwarded_for"';

#access_log  logs/access.log  main;

	sendfile        on;
#tcp_nopush     on;

#keepalive_timeout  0;
#keepalive_timeout  65;

#gzip  on;
#


	upstream http_backend {
		server 127.0.0.1:2000;
	}

	server {

		server_name  localhost;
		listen       8081 ssl http2;

		ssl_certificate /Users/abc/box2.crt;
		ssl_certificate_key /Users/abc/box2.key;

#charset koi8-r;

#access_log  logs/host.access.log  main;

		location "/dsb" {

			proxy_pass http://http_backend;

		}

#error_page  404              /404.html;

# redirect server error pages to the static page /50x.html
#
		error_page   500 502 503 504  /50x.html;
		location = /50x.html {
			root   html;
		}

# proxy the PHP scripts to Apache listening on 127.0.0.1:80
#
#location ~ \.php$ {
#    proxy_pass   http://127.0.0.1;
#}

# pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
#
#location ~ \.php$ {
#    root           html;
#    fastcgi_pass   127.0.0.1:9000;
#    fastcgi_index  index.php;
#    fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
#    include        fastcgi_params;
#}

# deny access to .htaccess files, if Apache's document root
# concurs with nginx's one
#
#location ~ /\.ht {
#    deny  all;
#}
	}


# another virtual host using mix of IP-, name-, and port-based configuration
#
#server {
#    listen       8000;
#    listen       somename:8080;
#    server_name  somename  alias  another.alias;

#    location / {
#        root   html;
#        index  index.html index.htm;
#    }
#}


# HTTPS server
#
#server {
#    listen       443 ssl;
#    server_name  localhost;

#    ssl_certificate      cert.pem;
#    ssl_certificate_key  cert.key;

#    ssl_session_cache    shared:SSL:1m;
#    ssl_session_timeout  5m;

#    ssl_ciphers  HIGH:!aNULL:!MD5;
#    ssl_prefer_server_ciphers  on;

#    location / {
#        root   html;
#        index  index.html index.htm;
#    }
#}
	include servers/*;
			 }

[Maxim Dounin]

HTTP/2 do not provide an equivalent to the Upgrade mechanism as available in HTTP/1.1, and hence WebSockets cannot be used with HTTP/2. Browsers typically use HTTP/1.1 for WebSocket requests.

[Sergey Kandaurov]

See also ​https://tools.ietf.org/html/rfc8441