The following utility can be used for auto-completion of commands:
$ which aws_completer
/usr/bin/aws_completer
$ complete -C '/usr/bin/aws_completer' aws
For future shell sessions, consider add this to your ~/.bashrc
$ echo "complete -C '/usr/bin/aws_completer' aws" >> ~/.bashrc
To check, type:
$ aws ec
Press the [TAB] key, it should add 2 automatically:
$ aws ec2