Serving two sites from one server with Nginx

The documentation says:

The default_server parameter, if present, will cause the server to become the default server for the specified address:port pair.

It's also obvious, there can be only one default server.

And it is also says:

A listen directive can have several additional parameters specific to socket-related system calls. They can be specified in any listen directive, but only once for the given address:port pair.

So, you should remove default and deferred from one of the listen 80 directives. And same applies to ipv6only=on directive as well.

Just hit this same issue, but the duplicate default_server directive was not the only cause of this message.

You can only use the backlog parameter on one of the server_name directives.

Example

site 1:

server {
    listen 80 default_server backlog=2048;
    server_name www.example.com;
    location / {
        proxy_pass http://www_server;
    }

site 2:

server {
    listen 80;    ## NOT NOT DUPLICATE THESE SETTINGS 'default_server backlog=2048;'
    server_name blogs.example.com;
    location / {
        proxy_pass http://blog_server;
    }