def maintenance_mode_on(dynamodb_client, dynamodb_table_name, maintenance_mode_key):
    """
    If maintenance mode is on, then the key `maintenance_mode_key` will be present
    and an Item will be returned in the response to `get_item`. If there is no
    item, that key will be absent from the response.
    """
    response = dynamodb_client.get_item(
            TableName=dynamodb_table_name,
            Key={'LockType': {'S': maintenance_mode_key}},
            ConsistentRead=True,
    )
    return 'Item' in response