Blocking non existing server_name in NginX

Server names are defined using the server_name directive and determine which server block is used for a given request. See also “How nginx processes a request”. They may be defined using exact names, wildcard names, or regular expressions:

NginX behaves in a way, such that,

Nginx first decides which server should process the request. Let’s start with a simple configuration where all three virtual servers listen on port *:80:

server {
    listen      80;
    server_name www.yasassri.org;
    ...
}

server {
    listen      80;
    server_nam www.yasassri.net;
    ...
}

server {
    listen      80;
    server_name www.yasassri.com;
    ...
}

In the above configuration Nginx checks only the request’s header field “Host” to determine which server the request should be routed to. If its value does not match any server name, or the request does not contain this header field at all, then Nginx will route the request to the default server for this port.

Let me elaborate this with an example, If a client sends a request to www.yasassri.org or www.yasassri.net or www.yasassri.com NginX will route the messages to the corresponding server block. (If the Host header contains the Host-name) But what if client sends a message with Host Header www.abcd.com, this message doesn't match with any server names, so it shouldn't be routed anywhere Right? No that's not what really happens, the default behavior of NginX is to route this message to the default server configuration. In the configuration above, the default server is the first one — this is Nginx’s standard default behavior. It can also be set explicitly which server should be default, with the default_server parameter in the listen directive:

server {
    listen      80 default_server;
    server_name example.net www.yasassri.net;
    ...
}

So what if you want to block all the calls that doesn't match with the defined server names? NginX doesn't provide a cofiguration for this, to achieve this you can simply add the following server blocks as a workaround. So the following will be your default server block.

server {
  listen 80 default_server;
  return 404;
}

So when ever your server name doesn't match the request will be routed to the above server block, and a 404 is sent to the client.

So that's it, please drop a comment if you have more queries.