How to Setup SSH on EC2 Instances

I have created two EC2 instances on AWS. I created a key pair for each of them. I downloaded the .pem private keys and converted them into .ppk format. I can connect to each of my ec2 instances using PuTTY and their .ppk private key. But how do I SSH from one of my ec2 instance to the other? I can ping the Public DNS of either of them from the other. But if I try ssh from one to the other, I get:

Permission denied (publickey).

Setup SSH connection

On server A, run below command

ssh-keygen

Hit enter enter enter. You’ll have two files:

.ssh/id_rsa
.ssh/id_rsa.pub

On Server A, cat and copy to clipboard the public key:

cat ~/.ssh/id_rsa.pub
[select and copy to your clipboard]

Log onto server B, and add the public key from server A to authorized_keys file

vi ~/.ssh/authorized_keys
[paste your clipboard contents]
[save and close]

Now ssh from server A:

ssh <username>@<server_B>

Repeat the process from server B to server A if you want to setup ssh connection in the opposite direction.