Print external host name of EC2 instance
Solution 1:
From within the instance, you can hit the Instance Metadata Service:
curl http://169.254.169.254/latest/meta-data/public-hostname
or
curl http://instance-data.ec2.internal/latest/meta-data/public-hostname
A wide variety of data is available via this interface.
Solution 2:
/opt/aws/bin/ec2-metadata -p will print the public hostname of that instance.