Nginx proxy with WebSockets

nginx_config

map $http_upgrade $connection_upgrade {
    default     upgrade;
    ''          close;
}

server {
        listen                          80;
        server_name                     example.com;
        location / {
                proxy_pass              http://localhost:1337;
                proxy_http_version      1.1;
                proxy_set_header        Upgrade $http_upgrade;
                proxy_set_header        Connection $connection_upgrade;
        }
}