upstream low_priority {
    server host1.example.com;
    server host2.example.com;
}

upstream medium_priority {
    server host1.example.com;
    server host2.example.com;
    server host3.example.com;
    server host4.example.com;
}

upstream high_priority {
    server host1.example.com;
    server host2.example.com;
    server host3.example.com;
    server host4.example.com;
    server host5.example.com;
    server host6.example.com;
}

server {
    listen 80;
    server_name example.com;

    location /low-priority-order {
        proxy_pass http://low_priority;
    }

    location /medium-priority-order {
        proxy_pass http://medium_priority;
    }

    location /high-priority-order {
        proxy_pass http://high_priority;
    }
}