If you run a bootstrap script that uses AWS CLI, you’ve probably run into an intermittent fatal error that says, “Unable to locate credentials”. IAM Roles should just work on the instance, but the credentials are not reliable in my experience on Linux systems. Before I attempt to run any bootstrap script, I use the following code to ensure the IAM credentials are where they should be.

config_exists=$(aws configure list | grep access_key | grep iam-role);
until [ ! -z "$config_exists" ]; do echo 'Amazon is playing games here. Trying to get IAM creds that should already be here ...'; sleep 2; config_exists=$(aws configure list | grep access_key | grep iam-role); done;