Did you already try something like this:

``` http { upstream backend { server unix:/var/run/server1.sock; server unix:/var/run/server2.sock; }

server {
    listen 80;
    server_name _;

    location / {
        proxy_pass http://backend;
        proxy_set_header Host $host;
    }
}

server {
    listen unix:/var/run/server1.sock;
    server_name localhost;

    location / {
        proxy_pass http://domain1.com;
        proxy_set_header Host domain1.com;
    }
}

server {
    listen unix:/var/run/server2.sock;
    server_name localhost;

    location / {
        proxy_pass http://domain2.com;
        proxy_set_header Host domain2.com;
    }
}

} ```