gistfile1.txt

map $time_iso8601 $upstream {
    default "app-b.example.org";
    "~T(0|1[01])" "app-a.example.org";
}

server {
    server_name app.example.org;
    location / {
      proxy_pass http://127.0.0.1;
      proxy_set_header Host $upstream;
    }
}

upstream app-a {
    server app-a.example.net;
}

server {
    server_name app-a.example.org;
    access_log /var/log/nginx/app-a.access.log;
    location / {
        proxy_pass http://app-a;
    }
}

upstream app-b {
    server app-b.example.net;
}

server {
    server_name app-b.example.org
    access_log /var/log/nginx/app-b.access.log;
    location / {
        proxy_pass http://app-b;
    }
}