[GitHub] [airflow] dstandish commented on a diff in pull request #28300: Add Public Interface description to Airflow documentation

[GitBox <gi...@apache.org>]

dstandish commented on code in PR #28300:
URL: https://github.com/apache/airflow/pull/28300#discussion_r1058624408


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docs/apache-airflow/administration-and-deployment/public-airflow-interface.rst:
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+ .. 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.
+
+Public Interface of Airflow
+===========================
+
+The Public Interface of Apache Airflow is a set of programmatic interfaces that allow developers to interact
+with and access certain features of the Apache Airflow system. This includes operations such as
+creating and managing DAGs (directed acyclic graphs), managing tasks and their dependencies,
+and extending Airflow capabilities by writing new executors, plugins, operators and providers. The
+Public Interface can be useful for building custom tools and integrations with other systems,
+and for automating certain aspects of the Airflow workflow.
+
+You can extend Airflow in three ways:
+
+* By writing new custom Python code (via Operators, Plugins, Provider)
+* By using the `Stable REST API <stable-rest-api-ref>`_ (based on the OpenAPI specification)
+* By using the `Airflow Command Line Interface (CLI) <cli-and-env-variables-ref.rst>`_
+
+How can you extend Apache Airflow with custom Python Code?
+==========================================================
+
+The Public Interface of Airflow consists of a number of different classes and packages that provide access
+to the core features and functionality of the system.
+
+The classes and packages that may be considered as the Public Interface include:
+
+* The :class:`~airflow.DAG`, which provides a way to define and manage DAGs in Airflow.
+* The :class:`~airflow.models.baseoperator.BaseOperator`, which provides a way write custom operators.
+* The :class:`~airflow.hooks.base.BaseHook`, which provides a way write custom hooks.
+* The :class:`~airflow.models.connection.Connection`, which provides access to external service credentials and configuration.
+* The :class:`~airflow.models.variable.Variable`, which provides access to Airflow configuration variables.
+* The :class:`~airflow.models.xcom.XCom` which are used to access to inter-task communication data.
+* The :class:`~airflow.secrets.BaseSecretsBackend` which are used to define custom secret managers.
+* The :class:`~airflow.plugins_manager.AirflowPlugin` which are used to define custom plugins.
+* The :class:`~airflow.triggers.base.BaseTrigger`, which are used to implement custom Custom Deferrable Operators (based on ``asyncio``).
+* The :class:`~airflow.decorators.base.TaskDecorator`, which provides a way write custom decorators.
+* The :class:`~airflow.listeners.listener.ListenerManager` class which provides hooks that can be implemented to respond to DAG/Task lifecycle events.
+
+.. versionadded:: 2.5
+
+   Listener public interface has been added in version 2.5.
+
+* The :class:`~airflow.executors.base_executor.BaseExecutor` - the Executors are the components of Airflow
+  that are responsible for executing tasks.
+
+.. versionadded:: 2.6
+
+   There are a number of different executor implementations built-in Airflow, each with its own unique
+   characteristics and capabilities. Executor interface was available in earlier version of Airflow but
+   only as of version 2.6 executors are fully decoupled and Airflow does not rely on built-in set of executors.
+   You could have implemented (and succeeded) with implementing Executors before Airflow 2.6 and a number
+   of people succeeded in doing so, but there were some hard-coded behaviours that preferred in-built
+   executors, and custom executors could not provide full functionality that built-in executors had.
+
+
+What is not part of the Public Interface of Apache Airflow?
+===========================================================
+
+Everything not mentioned in this document should be considered as non-Public Interface.

Review Comment:
   This doesn't address providers, or how we can include "private" e.g. helper code in otherwise "public" modules / classes.
   
   Is it sufficient to include `:meta private:`?  Or must we prefix with underscore?



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