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| <blockquote> |
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| <div class="section" id="cross-dag-dependencies"> |
| <span id="howto-operator-cross-dag-dependencies"></span><h1>Cross-DAG Dependencies<a class="headerlink" href="#cross-dag-dependencies" title="Permalink to this headline">¶</a></h1> |
| <p>When two DAGs have dependency relationships, it is worth considering combining them into a single |
| DAG, which is usually simpler to understand. Airflow also offers better visual representation of |
| dependencies for tasks on the same DAG. However, it is sometimes not practical to put all related |
| tasks on the same DAG. For example:</p> |
| <ul class="simple"> |
| <li><p>Two DAGs may have different schedules. E.g. a weekly DAG may have tasks that depend on other tasks |
| on a daily DAG.</p></li> |
| <li><p>Different teams are responsible for different DAGs, but these DAGs have some cross-DAG |
| dependencies.</p></li> |
| <li><p>A task may depend on another task on the same DAG, but for a different <code class="docutils literal notranslate"><span class="pre">execution_date</span></code>.</p></li> |
| </ul> |
| <p><code class="docutils literal notranslate"><span class="pre">ExternalTaskSensor</span></code> can be used to establish such dependencies across different DAGs. When it is |
| used together with <code class="docutils literal notranslate"><span class="pre">ExternalTaskMarker</span></code>, clearing dependent tasks can also happen across different |
| DAGs.</p> |
| <div class="section" id="externaltasksensor"> |
| <h2>ExternalTaskSensor<a class="headerlink" href="#externaltasksensor" title="Permalink to this headline">¶</a></h2> |
| <p>Use the <a class="reference internal" href="../../_api/airflow/sensors/external_task_sensor/index.html#airflow.sensors.external_task_sensor.ExternalTaskSensor" title="airflow.sensors.external_task_sensor.ExternalTaskSensor"><code class="xref py py-class docutils literal notranslate"><span class="pre">ExternalTaskSensor</span></code></a> to make tasks on a DAG |
| wait for another task on a different DAG for a specific <code class="docutils literal notranslate"><span class="pre">execution_date</span></code>.</p> |
| <div class="example-block-wrapper docutils container"> |
| <p class="example-header example-header--with-button"><span class="example-title">airflow/example_dags/example_external_task_marker_dag.py</span><a class="example-header-button viewcode-button reference internal" href="../../_modules/airflow/example_dags/example_external_task_marker_dag.html"><span>View Source</span></a></p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span> <span class="n">child_task1</span> <span class="o">=</span> <span class="n">ExternalTaskSensor</span><span class="p">(</span><span class="n">task_id</span><span class="o">=</span><span class="s2">"child_task1"</span><span class="p">,</span> |
| <span class="n">external_dag_id</span><span class="o">=</span><span class="n">parent_dag</span><span class="o">.</span><span class="n">dag_id</span><span class="p">,</span> |
| <span class="n">external_task_id</span><span class="o">=</span><span class="n">parent_task</span><span class="o">.</span><span class="n">task_id</span><span class="p">,</span> |
| <span class="n">mode</span><span class="o">=</span><span class="s2">"reschedule"</span><span class="p">)</span> |
| </pre></div> |
| </div> |
| </div> |
| </div> |
| <div class="section" id="externaltaskmarker"> |
| <h2>ExternalTaskMarker<a class="headerlink" href="#externaltaskmarker" title="Permalink to this headline">¶</a></h2> |
| <p>If it is desirable that whenever <code class="docutils literal notranslate"><span class="pre">parent_task</span></code> on <code class="docutils literal notranslate"><span class="pre">parent_dag</span></code> is cleared, <code class="docutils literal notranslate"><span class="pre">child_task1</span></code> |
| on <code class="docutils literal notranslate"><span class="pre">child_dag</span></code> for a specific <code class="docutils literal notranslate"><span class="pre">execution_date</span></code> should also be cleared, <code class="docutils literal notranslate"><span class="pre">ExternalTaskMarker</span></code> |
| should be used. Note that <code class="docutils literal notranslate"><span class="pre">child_task1</span></code> will only be cleared if “Recursive” is selected when the |
| user clears <code class="docutils literal notranslate"><span class="pre">parent_task</span></code>.</p> |
| <div class="example-block-wrapper docutils container"> |
| <p class="example-header example-header--with-button"><span class="example-title">airflow/example_dags/example_external_task_marker_dag.py</span><a class="example-header-button viewcode-button reference internal" href="../../_modules/airflow/example_dags/example_external_task_marker_dag.html"><span>View Source</span></a></p> |
| <div class="highlight-python notranslate"><div class="highlight"><pre><span></span> <span class="n">parent_task</span> <span class="o">=</span> <span class="n">ExternalTaskMarker</span><span class="p">(</span><span class="n">task_id</span><span class="o">=</span><span class="s2">"parent_task"</span><span class="p">,</span> |
| <span class="n">external_dag_id</span><span class="o">=</span><span class="s2">"example_external_task_marker_child"</span><span class="p">,</span> |
| <span class="n">external_task_id</span><span class="o">=</span><span class="s2">"child_task1"</span><span class="p">)</span> |
| </pre></div> |
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