Issue:
When you create an instance, but cannot connect to the VNC Server because of the error message, "Failed connect to server".
Reason:
Your nova vnc configuration may be mapped to wrong vnc server.
Solution:
1. vi /etc/nova/nova.conf
2. find vncserver_proxyclient_address
3. exam the value is valid and could be reached by your host.
4. Modify it to right server, e.g. 127.0.0.1
5. service openstack-nova-compute restart