The minecraft server runs but I cannot connect to the server with my minecraft client.
Running a Minecraft server on Cloud9 is against our Terms of Service and we have automated tools to block the game. Cloud9 is for development purposes only, not for hosting games. Feel free to develop Minecraft plugins using Cloud9 but you will not be able to run them on the platform. If you want a hosted Minecraft server there are plenty of other services out there, some for only a few dollars a month.
Thanks you and I have another question: How to create a clone of a workspace?