EC2 inbound from security group not working - what have I done wrong?

Question

I have two instances.

IOne is in us-east-1b and is in security group 'bamboo'

ITwo is in us-east-1c and is in security group 'ssh from bamboo'

In ssh from bamboo I allow inbound traffic on port 22 from group 'bamboo'

This results in IOne getting timeouts when trying to SSH into ITwo

If I change the security rule to the IP address of IOne instead of the group name, the SSH connection succeeds.

I read that the two machines have to be in the same region (though it doesn't mention zones). Should my above setup work? If not what would I need to change?

Answer 1

Maybe this answer is late but @datasage probably was right. You need to use your private IP and not the public or Elastic IP

From the AWS EC2 documentation:

Incoming traffic is allowed based on the private IP addresses of the instances that are associated with the source security group (and not the public IP or Elastic IP addresses).

Answer 2

You can't use the public IP, but you can use the public hostname (ec2-IPADDRESS-.us-east-1.compute.amazonaws.com) because this will resolve to the internal IP address when called from inside EC2, and will resolve to the external IP from outside Amazon's network.