Recover broken Amazon EC2 instance

Sometimes shit happens, accidentally.
Especially  when you lost ssh access to your virtual server (e.g. due to errors in  ~/.ssh/authorized_keys, /etc/sudoers, /etc/group, /etc/shadow or another important config file).

When you catch errors like:

No supported authentication methods available

or

sudo
sudo: >>> /etc/sudoers: syntax error near line 1 <<<
sudo: parse error in /etc/sudoers near line 1
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin


Don't worry, inside the Amazon cloud you can repair almost all.

Follow these simple steps to solve the problem:

1. Via AWS console:
1. Launch new temporary EC2 micro-instance in the same availability zone.
2. Stop broken instance.
3. Detach root EBS volume from the broken instance.
4. Attach this EBS to the temporary instance (as /dev/sdf).
2. Via SSH console from the temporary instance:
1. Mount this EBS:
   sudo mount /dev/xvdf /mnt
2. Fix all problems on mounted file system.
3. Unmount this EBS:
   sudo umount /mnt
3. Via AWS console:
1. Detach this EBS from the temporary instance.
2. Attach this EBS to the broken instance (as /dev/sda1).
3. Start broken instance.
4. Check that broken instance now is healthy (available via ssh and everything is functioning normally).
5. Then you can stop temporary instance (or terminate it).

I hope this article will make someone little bit happy)