How can I allow both www URLs and non-www URLs for the same same site under nginx?

Question

My problem is about www and non www urls. I use nginxCP, a distribution of nginx that includes cPanel and WHM.

I need to be able to surf my sites hosted by this server with both non-www and www urls. Ex: when I type www.example.com I surf this site with the www. When I type example.com, I surf this site WITHOUT the www. I don't want a redirect between the two.

I have included my config files for nginx and a site's vhost (that is automatically generated by nginxCP).

/etc/nginx/nginx.config:

user  nobody;
# no need for more workers in the proxy mode
worker_processes  auto;
error_log  /var/log/nginx/error.log warn;
worker_rlimit_nofile 20480;
events {
 worker_connections 5120; # increase for busier servers
 use epoll; # you should use epoll here for Linux kernels 2.6.x
}
http {

 server_name_in_redirect on;
 server_names_hash_max_size 10240;
 server_names_hash_bucket_size 1024;
 include    mime.types;
 default_type  application/octet-stream;
 server_tokens off;
# remove/commentout disable_symlinks if_not_owner;if you get Permission denied error
# disable_symlinks if_not_owner;
 sendfile on;
 tcp_nopush on;
 tcp_nodelay on;
 keepalive_timeout  5;
 gzip on;
 gzip_vary on;
 gzip_disable "MSIE [1-6]\.";
 gzip_proxied any;
 gzip_http_version 1.0;
 gzip_min_length  1000;
 gzip_comp_level  6;
 gzip_buffers  16 8k;
# You can remove image/png image/x-icon image/gif image/jpeg if you have slow CPU
 gzip_types    text/plain text/xml text/css application/x-javascript application/xml application/javascript application/xml+rss text/javascript application/atom+xml;
 ignore_invalid_headers on;
 client_header_timeout  3m;
 client_body_timeout 3m;
 send_timeout     3m;
 reset_timedout_connection on;
 connection_pool_size  256;
 client_header_buffer_size 256k;
 large_client_header_buffers 4 256k;
 client_max_body_size 200M;
 client_body_buffer_size 128k;
 request_pool_size  32k;
 output_buffers   4 32k;
 postpone_output  1460;
 proxy_temp_path  /tmp/nginx_proxy/;
 proxy_cache_path /var/cache/nginx levels=1:2 keys_zone=microcache:15m inactive=24h max_size=500m;
 client_body_in_file_only on;
 log_format bytes_log "$msec $bytes_sent .";
 log_format custom_microcache '$remote_addr - $remote_user [$time_local] '
        '"$request" $status $body_bytes_sent '
        '"$http_referer" "$http_user_agent" nocache:$no_cache';
include "/etc/nginx/vhosts/*";
}

/etc/nginx/vhosts/mysite.com:

server {
          error_log /var/log/nginx/vhost-error_log warn;
          listen xxx.xxx.xxx.xxx:80;
          listen [::]:80;
          server_name www.mysite.com mysite.com;
          access_log /usr/local/apache/domlogs/mysite.com-bytes_log bytes_log;
          access_log /usr/local/apache/domlogs/mysite.com combined;
          root /home/syriosrl/public_html;
          #location / {
          location ~*.*\.(3gp|gif|jpg|jpeg|png|ico|wmv|avi|asf|asx|mpg|mpeg|mp4|pls|mp3|mid|wav|swf|flv|html|htm|txt|js|css|exe|zip|tar|rar|gz|tgz|bz2|uha|7z|doc|docx|$
          expires 1M;
          try_files $uri @backend;
          }
          location / {
          error_page 405 = @backend;
          add_header X-Cache "HIT from Backend";
          proxy_pass http://xxx.xxx.xxx.xxx:8081;
          include proxy.inc;
          include microcache.inc;
          }
          location @backend {
          internal;
          proxy_pass http://xxx.xxx.xxx.xxx:8081;
          include proxy.inc;
          include microcache.inc;
          }
          location ~ .*\.(php|jsp|cgi|pl|py)?$ {
          proxy_pass http://xxx.xxx.xxx.xxx:8081;
          include proxy.inc;
          include microcache.inc;
          }
          location ~ /\.ht {
          deny all;
          }
        }

Answer 1

I resolved it after a deep study of my sites. In my server I have two sites: the first is written by me (a managerial software), and the second uses WordPress. I noticed out that the first site can be surfed with www and without-www, so I deduced that the problem wasn't the web server, but the CMS. After some researches on the web about this thing, I found out that WordPress (and also Magento) forces all the urls to be non-www (or the contrary, depending on WP version). I fixed this problem with WP by adding this few line of code at the end of wp-config.php file, in the site's root:

$hostname = $_SERVER['SERVER_NAME'];
define('WP_SITEURL', 'http://' . $hostname);
define('WP_HOME', 'http://' . $hostname);

In Magento I can fix this problem with these methods: https://docs.nexcess.net/article/changing-magento-base-urls.html

Ps: if you want to test the non-CMS site's urls are http://www.merlinimediazioni.com and http://merlinimediazioni.com ; the CMS site's urls are http://www.mattiamerlini.it and http://mattiamerlini.it . When you load one of these urls you can notice that if you have inserted www.mattiamerlini.it the url remain with www, and viceversa for non-www.

Thank you for your time and help

Have a nice weekend