Add Docker stack example for Python venv

docker-stack-docs/build.rst

@@ -477,6 +477,28 @@ Note that similarly when adding individual packages, you need to use the ``airfl
     :language: text
 
 
+Example of adding a Python venv for ``ExternalPythonOperator``
+..............................................................
+
+The following example creates a separate Python virtualenv inside the image and installs packages
+from ``requirements.txt`` into it, leaving Airflow's own Python environment untouched. This is the
+typical setup for the
+:ref:`ExternalPythonOperator <apache-airflow-providers-standard:howto/operator:externalpythonoperator>`
+(or the ``@task.external_python`` decorator), which executes tasks in a pre-existing, immutable
+Python environment. Use ``/opt/airflow/venv/bin/python`` as the operator's ``python`` argument
+to run tasks in this venv.
+
+The venv is created without ``--system-site-packages``, so the packages installed inside it
+are isolated from Airflow's own dependencies.
+
+.. exampleinclude:: docker-examples/extending/add-python-venv/Dockerfile
+    :language: Dockerfile
+    :start-after: [START Dockerfile]
+    :end-before: [END Dockerfile]
+
+.. exampleinclude:: docker-examples/extending/add-python-venv/requirements.txt
+    :language: text
+
 Example when writable directory is needed
 .........................................
 

docker-stack-docs/docker-examples/extending/add-python-venv/Dockerfile

@@ -0,0 +1,24 @@
+# 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.
+
+# This is an example Dockerfile. It is not intended for PRODUCTION use
+# [START Dockerfile]
+FROM apache/airflow:3.4.0
+COPY requirements.txt /
+RUN python -m venv /opt/airflow/venv \
+    && /opt/airflow/venv/bin/pip install --no-cache-dir -r /requirements.txt
+# [END Dockerfile]

docker-stack-docs/docker-examples/extending/add-python-venv/requirements.txt

@@ -0,0 +1 @@
+colorama==0.4.0