Copy SSH keys to each node

gistfile1.txt

This step is optional, but it allow us to easily SSH into each node without using a password. 
I'll use the ssh-copy-id command to copy my public key to the remote server.

If you don't have a key generated already, you can do so with:

ssh-keygen -t rsa

Hit enter twice and leave the passphrase empty (unless you really want to use a passphrase).

Then copy the key to each node with:

ssh-copy-id pi@docker1

You'll have to enter your password to copy the key. Do this for each node.