When you sign up at Clustermin, we create a secure SSH key with a passphrase for your account. It will allow you to connect to your servers at the first time without using a password. When the server is connected, we'll create a separated SSH key for each server.
No password = more secure.
To get your account SSH key, please visit Account > SSH key, then click Copy to get it.
You can add that SSH key to your DigitalOcean account by clicking your Profile > Settings > Security, Add SSH key. Just paste the copied SSH key into a form, give it a name .e.g "Clustermin", then submit.
From now on, justs select the "Clustermin" SSH key every time you create new servers. When the server is created, you can now connect it to Clustermin just by the IP address.