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Step Four—Spin Up a New Server
The previous steps have explained how to set up a server with pre-installed SSH keys. You cannot, however, use the control panel to add keys to already created droplets.

In order to add additional keys to pre-existing droplets, you can paste in the keys using SSH:

cat ~/.ssh/id_rsa.pub | ssh root@[your.ip.address.here] "cat >> ~/.ssh/authorized_keys"
When actually spinning up a new server, select the keys that you would like installed on your server from the "Create a Droplet" screen. You can select as many keys as you like: