Fix permission denied (publickey) when SSH Access to Amazon EC2

I accidentally messed up the /home/ubuntu/.ssh/authorized_keys of AWS EC2, and cannot access EC2 from SSH. Here are the steps for fixing it:

1. Detach the bad EBS volume.

2. Create a new EC2 instance, and attach that bad EBS volume to it.

3. Mount that bad EBS volume from the new created EC2 instance.

   sudo mount /dev/xvdb1 /vol
   

4. Fix the /home/ubuntu/.ssh/authorized_keys, and umount and detach the EBS volume.

   sudo umount /vol
   

5. Attach the fixed EBS volume to root device /dev/sda1 of the origin EC2 instance.

Reference:

• Making an Amazon EBS Volume Available for Use on Linux
• how change root device on instance