def _instance_tags(hostname, role, tags=None):
    """Return instance tags (common tags + instance name and role).
    """
    if tags is None:
        tags = []

    return [{
        'ResourceType': 'instance',
        'Tags': tags + [
            {'Key': 'Name', 'Value': hostname.lower()},
            {'Key': 'Role', 'Value': role.lower()},
        ],
    }]