Back to Repositories

Testing Watcher Task Failure Propagation in Apache Airflow

This test suite validates the watcher task functionality in Apache Airflow, specifically focusing on failure propagation and trigger rules. The watcher task acts as a monitoring mechanism to detect and handle upstream task failures in DAG execution.

Test Coverage Overview

The test coverage focuses on the watcher task’s failure handling capabilities and trigger rule implementation.

Key areas tested include:

ONE_FAILED trigger rule activation
Exception propagation through DAG runs
Zero retry behavior validation
Upstream task failure detection

Implementation Analysis

The testing approach employs Airflow’s task decorator pattern with specific trigger rule configuration. The implementation validates the watcher task’s behavior when upstream tasks fail, ensuring proper exception handling and DAG status propagation.

Technical patterns include:

Task decorator usage with TriggerRule.ONE_FAILED
AirflowException handling
Retry configuration validation

Technical Details

Testing infrastructure includes:

Airflow’s native testing framework
Task decorator functionality
TriggerRule enumeration
Exception handling mechanisms
Zero retry configuration

Best Practices Demonstrated

The test suite exemplifies robust error handling practices in Airflow DAG design.

Notable practices include:

Clear failure propagation mechanisms
Explicit trigger rule definition
Controlled retry behavior
Descriptive exception messaging
Proper task decoration implementation

apache/airflow

tests_common/test_utils/watcher.py

            
# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership.  The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#   http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied.  See the License for the
# specific language governing permissions and limitations
# under the License.
from __future__ import annotations

from airflow.decorators import task
from airflow.exceptions import AirflowException
from airflow.utils.trigger_rule import TriggerRule


@task(trigger_rule=TriggerRule.ONE_FAILED, retries=0)
def watcher():
    """
    Watcher task.

    Watcher task raises an AirflowException and is used to 'watch' tasks for failures
    and propagates fail status to the whole DAG Run.
    """
    raise AirflowException("Failing task because one or more upstream tasks failed.")