What ports are required to be open on Ubuntu Cloud Guests running juju client instances? As far as I understand, Zookeeper needs to communicate with all its nodes -- So that is one requirement.. Anything else? Also what are the ports that are used by zookeeper? I need these so that I can put some security rules on my EC2 instances..
2181 is the ZooKeeper port, and does need to be open, but only from the agents to the zookeeper server. From outside going into that server, the juju client always tunnels everything over SSH.
This, however, is not actually necessary for you to know. Juju provisions the EC2 instances that it will use, and so, it also assigns security groups to them, and handles all security group authorization. You can of course use the EC2 API to assign your own, but you don't actually have to, as juju automates it.