Basic troubleshooting

The first test we should perform is a simple ping from the blog server to the database server. This will quickly answer whether the two servers are able to communicate at all:

[blog]$ ping db.example.com
PING db.example.com (192.168.33.12) 56(84) bytes of data.
64 bytes from db.example.com (192.168.33.12): icmp_seq=1 ttl=64 time=0.420 ms
64 bytes from db.example.com (192.168.33.12): icmp_seq=2 ttl=64 time=0.564 ms
64 bytes from db.example.com (192.168.33.12): icmp_seq=3 ttl=64 time=0.562 ms
64 bytes from db.example.com (192.168.33.12): icmp_seq=4 ttl=64 time=0.479 ms
^C
--- db.example.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3006ms
rtt min/avg/max/mdev = 0.420/0.506/0.564/0.062 ms

From the ping command's results we can see that the blog server can communicate with the database server, or rather, the blog server sent an ICMP echo request and received an ICMP echo reply from the database server. The next connectivity we can test...