On the cluster tab, make sure you cluster controller looks like this. You private network interface needs to have DHCP and DNS.
Edit the private network interface. Make sure your IP's and management is set correctly. If you don't have a router on your private network, make the router IP the IP of the private interface on your MAAS server.
This is under the settings gear in the MAAS gui, make sure you have your forward DNS server set correctly and your proxy.