def _ensure_default_vpc(client):
    """
    Ensures that there is a default VPC available in the region used by the boto3 EC2 client.
    Create the default VPC if it doesn't exist.
    """

    default_vpc_filter_expression = [{
        'Name': 'isDefault',
        'Values': ['true'],
    }]

    res = client.describe_vpcs(Filters=default_vpc_filter_expression)

    if res['Vpcs']:
        return res['Vpcs'][0]['VpcId']
    else:
        return client.create_default_vpc()['Vpc']['VpcId']