Can you describe what your network configuration is within the cluster? More specifically consider these following questions you should be verifying within your deploy (dont post hostnames or IP's plz).
I believe EC2 nodes are multi-homed. Validate for yourself what the host-naming is resolving to across those interfaces. Look at what forward and reverse lookups are returning as well.
Some of the network configuraitons for components have a "wildcard" name that can be found when you search within a service's configuration settings. This is so the service is listening on "all" interfaces.
For yourself, from both the EC2 cluster nodes you are trying to connect to, and your VM, please evaluate what comes back for this command line in comparison to the naming you are using between your VM and the EC2 environment:
# python -c "import socket; print socket.getfqdn(); print socket.gethostbyname(socket.getfqdn())"
