If ssh key pair lost, its not possible to connect to EC2 instances. But there is a method to get the access back and this article explains those steps in detail.
Step1: Login to AWS console.
Step2: Select the EC2 management page.
Step3: From the left menu, choose Key Pairs under Network & Security.
Step4: Select Create key pair and proceed.
Step5: Download new key pair.
Step6: Retrieve the public key from the key pair by following the steps mentioned in below url.
Step7: Select the required instance from list of instances in EC2 management page.
Step8: Stop the selected instance.
Step9: Choose Instance settings under Actions and Edit user data for the selected instance.
Step10: Copy the following script into the Edit user data dialog box.
#cloud-config ssh_deletekeys: false ssh_authorized_keys: - PUBLICKEY cloud_final_modules: - [ssh, always]
Here we need to replace PUBLICKEY with the public key starting with ssh-rsa retrieved earlier.
Step11: Start the instance.
Step12: Verify that instance is accessible using the new key.
Step13: Stop the instance again.
Step14: Choose Instance settings under Actions and Edit user data for the selected instance.
Step15: Delete all texts in the Edit user data dialog box and Save.
Step16: Start the instance.