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SSH

The client has the private key (contained on a .pem file), and the server the public key (a file with the .pub extension, saved at ~/.ssh/authorized_keys). Anyone with the public key can access the instance.

chmod 400 us-east-kp.pem # Fix WARNING: UNPROTECTED PRIVATE KEY FILE!
ssh -i us-east-kp.pem ec2-user@3.83.54.1
ssh -i us-east-kp.pem ec2-user@ec2-107-22-100-77.compute-1.amazonaws.com

Close connection: exit

You can generate the public key from the private key at any time with: ssh-keygen -y -f key.pem > key.pub source

Add an SSH key to an EC2 instance that is already launched​

Important: you need to connect to the machine using 'EC2 Instance Connect' to do this.

On the client, generate the SSH key pair:

ssh-keygen -b 2048 -t rsa # Name the file 'ec2_rsa' when prompted

This creates 2 files: ec2_rsa and ec2_rsa.pub.

Copy the contents of the public key to the clipboard with pbcopy < ec2_rsa.pub.

Connect to the EC2 instance via 'EC2 Instance Connect'.

Run sudo nano ~/.ssh/authorized_keys, paste the contents of the ec2_rsa.pub saved in your clipboard and save the file.

Finally, connect running ssh -i ec2_rsa ec2-user@3.83.54.1, where 3.83.54.1 is the public IPv4 address.