Issue:

When you created an instance inside Openstack, you may find that you cannot ping address by domain name in the instance. But ping IP Address directly is OK. 

For example, ping 74.125.200.99 is OK, but ping www.google.com will be failed, because of error ping: unknown host www.google.com. Whilst, the /etc/resolv.conf configuration is correct.

#Generated by NetworkManager

search openstacklocal
nameserver 8.8.8.8
nameserver 8.8.4.4

Root Cause:

This may be caused by your openstack firewall setting. UDP communication must be allowed. Otherwise, DNS Service packages will be blocked by firewall.

Solution:

Log into admin page to confirm if you have already enable all necessary Protocol Rules.