Cần cấu hình như sau: 
server {
    listen      xx.xx.xx.xx:443 ssl;
    server_name socketio.nentang.vn www.socketio.nentang.vn;
    ssl_certificate      /home/admin/conf/web/ssl.socketio.nentang.vn.pem;
    ssl_certificate_key  /home/admin/conf/web/ssl.socketio.nentang.vn.key;
    error_log  /var/log/httpd/domains/socketio.nentang.vn.error.log error;

    location / {
        proxy_pass      http://xx.xx.xx.xxx:PORT;

    proxy_set_header   X-Forwarded-For $remote_addr;
    proxy_set_header   Host $http_host;

#enable Web socket
    proxy_http_version 1.1;
    proxy_set_header   Upgrade $http_upgrade;
    proxy_set_header   Connection "upgrade";

        location ~* ^.+\.(jpeg|jpg|png|gif|bmp|ico|svg|tif|tiff|css|js|htm|html|ttf|otf|webp|woff|txt|csv|rtf|doc|docx|xls|xlsx|ppt|pptx|odf|odp|ods|odt|pdf|psd|ai|eot|eps|ps|zip|tar|tgz|gz|rar|bz2|7z|aac|m4a|mp3|mp4|ogg|wav|wma|3gp|avi|flv|m4v|mkv|mov|mpeg|mpg|wmv|exe|iso|dmg|swf)$ {
            root           /home/admin/web/socketio.nentang.vn/public_html;
            access_log     /var/log/httpd/domains/socketio.nentang.vn.log combined;
            access_log     /var/log/httpd/domains/socketio.nentang.vn.bytes bytes;
            expires        max;
            try_files      $uri @fallback;
        }
    }

    location /error/ {
        alias   /home/admin/web/socketio.nentang.vn/document_errors/;
    }

    location @fallback {
        proxy_pass      http://xx.xx.xx.xx:PORT;
    }

    location ~ /\.ht    {return 404;}
    location ~ /\.svn/  {return 404;}
    location ~ /\.git/  {return 404;}
    location ~ /\.hg/   {return 404;}
    location ~ /\.bzr/  {return 404;}

    include /home/admin/conf/web/snginx.socketio.nentang.vn.conf*;
}