Works great
I know this is an older AMI, but it works great. I'll address a few concerns that others likely hit.
SSH: Make sure your SG has the right IP/Host Name in it. You should get a request to accept the client cert on connection no matter the auth issues. If you get that, the connection worked.
Cert issues: For centos, the username is not ec2-user, it's 'centos'. It will error with messages about certs and connections if the user is wrong. That might steer you in the wrong direction. No user name given will request on on connection.
Try: centos@public-ip for the host names connection string. Make sure the private key is being passed to the connection as well (In putty, you'll find this under Connections -> SSH -> Auth, near the bottom of the page). If any of these three items are off, this fails.
Brother I don't know who you are but you are an Angel, I've been struggling this for 12 hours. Thank you