I recently noticed that I am running an old version of AWS CLI that is lacking some functionality I need:
$aws --version aws-cli/1.2.9 Python/3.4.3 Linux/3.1
From http://docs.aws.amazon.com/cli/latest/userguide/installing.html#install-with-pip
To upgrade an existing AWS CLI installation, use the --upgrade option:
pip install --upgrade awscli