Nginx 設定預設網站

Nginx 有多個 virtual host 時，可以在 listen 設定後面加上  default_server 參數，將該 virtual host設定為預設網站。
以下設定在所有 80 port virtual host 當 server_name 都不符合時，會回應 444。

server {
    listen       80  default_server;
    server_name  _;
    return       444;
}

若也要設定 https 預設網站，當 server_name 都不符合時，
亦會回應 444，可增加監聽 443 port，雖然是回應 444，但還是需要設定 SSL 憑證。
所以先產生憑證 (若沒/etc/nginx/ssl資料夾，可先自行建立)

$ openssl req -x509 -nodes -days 3650 -newkey rsa:2048 -keyout /etc/nginx/ssl/default_server.key -out /etc/nginx/ssl/default_server.crt

填完資料，即可產生憑證。
nginx 設定如下

sserver {
    listen       80  default_server;
    listen       443 default_server ssl;
    server_name  _;
    
    ssl_certificate /etc/nginx/ssl/default_server.crt;
    ssl_certificate_key /etc/nginx/ssl/default_server.key;
    
    return       444;
}

參考：
http://nginx.org/en/docs/http/server_names.html

listen 語法，http://nginx.org/en/docs/http/ngx_http_core_module.html

listen address[:port] [default_server] [ssl] [http2 | spdy] [proxy_protocol] [setfib=number] [fastopen=number] [backlog=number] [rcvbuf=size] [sndbuf=size] [accept_filter=filter] [deferred] [bind] [ipv6only=on|off] [reuseport] [so_keepalive=on|off|[keepidle]:[keepintvl]:[keepcnt]];

listen port [default_server] [ssl] [http2 | spdy] [proxy_protocol] [setfib=number] [fastopen=number] [backlog=number] [rcvbuf=size] [sndbuf=size] [accept_filter=filter] [deferred] [bind] [ipv6only=on|off] [reuseport] [so_keepalive=on|off|[keepidle]:[keepintvl]:[keepcnt]];

listen unix:path [default_server] [ssl] [http2 | spdy] [proxy_protocol] [backlog=number] [rcvbuf=size] [sndbuf=size] [accept_filter=filter] [deferred] [bind] [so_keepalive=on|off|[keepidle]:[keepintvl]:[keepcnt]];