Sometimes for some reason some VPN might not work as one expects. Then one can login to a node with a key.

First, check if you have a public key already. On your own computer in a terminal run:

cat ~/.ssh/id_rsa.pub

If this command worked, then skip the next step. If an error appeared, run this:

ssh-keygen

It will ask for a password. This is the password you give to the key. You can make one without password, in which case it will not ask for a password each time you try to use it.

You must have an access to the cluster somehow to run the following command:

ssh-copy-id -i ~/.ssh/id_rsa.pub <your-username>@cluster-address

Well, you can also just copy the string from id_rsa.pub on your machine to the id_rsa.pub on your cluster.

This trick does not work for all machines. So, you might use the established connection to connect to other machines. In my case I wanted to work with some notebooks, so I did:

ssh -N -L localhost:PORT1:localhost:PORT2 <your-username>@cluster-address

and so it worked.