nginx server_name wildcard or catch-all

Question

I have an instance of nginx running which serves several websites. The first is a status message on the server\'s IP address. The second is an admin console on admin.d

Answer 1

Only 1 server directive

From Nginx listen Docs

The default_server parameter, if present, will cause the server to become the default server for the specified address:port pair. If none of the directives have the default_server parameter then the first server with the address:port pair will be the default server for this pair.

If you only have 1 server directive, that will handle all request, you don't need to set anything.

---

Multiple server directive

If you want to match all request with specified server directive, just add default_server parameter to listen, Nginx will use this server directive as default.

server {
    listen 80 default_server;
}

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About server_name _;

From Nginx Docs

In catch-all server examples the strange name “_” can be seen:

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

There is nothing special about this name, it is just one of a myriad of invalid domain names which never intersect with any real name. Other invalid names like “--” and “!@#” may equally be used.

It doesn't matter what server_name you set, it is just an invalid domain name.