Changing Private-Public Key pair of an Existing Amazon EC2 Instance.

Changing private-public key pair of an existing amazon EC2 instance has been a constrain for me. I done lot of brainstorming on this. But in most of the places I found that taking new instance is the way or rather better option. But after lot of research I found out a way. It may not be straight forward but will do the job. But as a software engineer it is pleasure to do some creepy interesting things that will make life easier.We can do it in three steps.

Step 1: Creating New Key Pair

• Log in to AWS console
• Go to Services -> EC2 -> From left navigator(Menu on left side) select Key Pairs
• From there we can get the details of existing key pairs.
• Click on the Option "Create New Key Pair" from the top menu
• Give a name for New Key Pair and Click on create.The new key pair will be crated and downloaded as a pem file.

Step 2: Extracting Pubic Key From Key Pair

• Here we need to use the public key with SSH client.so weed to get public key based on that
• Use the following command for generating public key

  ssh-keygen -y -f private_key.pem > public_key.pub

Step 3: Replacing the Old Public Key with New in the Instance

• Log in to the Instance using Old Key Pair using ssh client
• Follow the below steps

1. cd ~/.ssh 

2. sudo vi authorized_keys

3. Open the new public key file(public_key.pub) and copy paste the content to "authorized_keys".
4. After a space add the Privet Key base name(For eg: Here private key name is "private_key.pem".So after public key put a space and add "private_key".)
5. Delete the old public key from the file "authorized_keys" and save

Now try to log in with new key pair. Its done.