Different SSH keys for different Droplets

I want to use different SSH keys for different droplets.

I already have a droplet that uses an SSH key named as the “default”: id_rsa and id_rsa.pub. So I want to use another key for another droplet.

I have tried creating a new SSH key pair by:

ssh-keygen -t rsa

Enter file in which to save the key (/Users/myUser/.ssh/id_rsa):   dropletName_rsa

Then I have tried to pass the public key to the server by:

cat ~/.ssh/dropletName_rsa.pub | ssh -p portNumber user@ipadress  "mkdir -p ~/.ssh && cat >>  ~/.ssh/authorized_keys"

The key is copied but when I tried to connect with SSH I am prompted with a password request.

If I copy the key with the “default” name: id_rsa.pub. The login without password works. But then I am using the same SSH key pair for two different droplets.

Which solution do you use to improve security?

Thanks,