upstream firstApp{
    server 127.0.0.1:8123;
}

server{
    server_name mydomain.com;
    access_log /var/log/nginx/me.log;

    location / {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $http_host;
        proxy_set_header X-NginX-Proxy true;

        proxy_pass http://firstApp/;
        proxy_redirect off;
    }
}

upstream otherapp{
    server 127.0.0.1:8124;
}

server{
    server_name otherapp.mydomain.com;
    access_log /var/log/nginx/me.log;

    location / {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $http_host;
        proxy_set_header X-NginX-Proxy true;

        proxy_pass http://otherapp/;
        proxy_redirect off;
    }
}