[GitHub] [airflow] ashb commented on a diff in pull request #28558: Make the policy functions pluggable

["ashb (via GitHub)" <gi...@apache.org>]

ashb commented on code in PR #28558:
URL: https://github.com/apache/airflow/pull/28558#discussion_r1103671445


##########
airflow/policies.py:
##########
@@ -0,0 +1,208 @@
+# 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 typing import TYPE_CHECKING
+
+import pluggy
+
+local_settings_hookspec = pluggy.HookspecMarker("airflow.policy")
+hookimpl = pluggy.HookimplMarker("airflow.policy")
+
+__all__: list[str] = ["hookimpl"]
+
+if TYPE_CHECKING:
+    from airflow.models.baseoperator import BaseOperator
+    from airflow.models.dag import DAG
+    from airflow.models.taskinstance import TaskInstance
+
+
+@local_settings_hookspec
+def task_policy(task: BaseOperator) -> None:
+    """
+    This policy setting allows altering tasks after they are loaded in the DagBag.
+
+    It allows administrator to rewire some task's parameters.  Alternatively you can raise
+    ``AirflowClusterPolicyViolation`` exception to stop DAG from being executed.
+
+    Here are a few examples of how this can be useful:
+
+    * You could enforce a specific queue (say the ``spark`` queue) for tasks using the ``SparkOperator`` to
+      make sure that these tasks get wired to the right workers
+    * You could enforce a task timeout policy, making sure that no tasks run for more than 48 hours
+
+    :param task: task to be mutated
+    """
+
+
+@local_settings_hookspec
+def dag_policy(dag: DAG) -> None:
+    """
+    This policy setting allows altering DAGs after they are loaded in the DagBag.
+
+    It allows administrator to rewire some DAG's parameters.
+    Alternatively you can raise ``AirflowClusterPolicyViolation`` exception
+    to stop DAG from being executed.
+
+    Here are a few examples of how this can be useful:
+
+    * You could enforce default user for DAGs
+    * Check if every DAG has configured tags
+
+    :param dag: dag to be mutated
+    """
+
+
+@local_settings_hookspec
+def task_instance_mutation_hook(task_instance: TaskInstance) -> None:
+    """
+    This setting allows altering task instances before being queued by the Airflow scheduler.
+
+    This could be used, for instance, to modify the task instance during retries.
+
+    :param task_instance: task instance to be mutated
+    """
+
+
+@local_settings_hookspec
+def pod_mutation_hook(pod) -> None:
+    """
+    Mutate pod before scheduling.
+
+
+    This setting allows altering ``kubernetes.client.models.V1Pod`` object before they are passed to the
+    Kubernetes client for scheduling.
+
+    This could be used, for instance, to add sidecar or init containers to every worker pod launched by
+    KubernetesExecutor or KubernetesPodOperator.
+    """
+
+
+@local_settings_hookspec(firstresult=True)
+def get_airflow_context_vars(context) -> dict[str, str]:
+    """
+    This setting allows getting the airflow context vars, which are key value pairs.  They are then injected
+    to default airflow context vars, which in the end are available as environment variables when running
+    tasks dag_id, task_id, execution_date, dag_run_id, try_number are reserved keys.
+
+    :param context: The context for the task_instance of interest.
+    """
+    ...
+
+
+@local_settings_hookspec(firstresult=True)
+def get_dagbag_import_timeout(dag_file_path: str) -> int | float:
+    """
+    This setting allows for dynamic control of the DAG file parsing timeout based on the DAG file path.
+
+    It is useful when there are a few DAG files requiring longer parsing times, while others do not.
+    You can control them separately instead of having one value for all DAG files.
+
+    If the return value is less than or equal to 0, it means no timeout during the DAG parsing.
+    """
+    ...
+
+
+class DefaultPolicy:
+    """:meta private:"""
+
+    # Default implementations of the policy functions
+
+    @staticmethod
+    @hookimpl
+    def get_dagbag_import_timeout(dag_file_path: str):
+        from airflow.configuration import conf
+
+        return conf.getfloat("core", "DAGBAG_IMPORT_TIMEOUT")
+
+    @staticmethod
+    @hookimpl
+    def get_airflow_context_vars(context):
+        return {}
+
+
+def make_plugin_from_local_settings(pm: pluggy.PluginManager, module, names: list[str]):
+    """
+    Turn the functions from airflow_local_settings module into a custom/local plugin, so that
+    plugin-registered functions can co-operate with pluggy/setuptool entrypoint plugins of the same methods.
+
+    Airflow local settings will "win" as they are the last plugin registered.

Review Comment:
   ```suggestion
       Airflow local settings will be "win" (i.e. they have the final say) as they are the last plugin registered.
   ```



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