 .. 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.

Extending the Chart
===================

The Airflow Helm Chart can be easily extended by creating a custom chart which will depend on the Airflow chart.
That can be useful in cases where there is a need for custom templates deployment (e.g. maintenance CronJobs),
which are not directly related to the Airflow Helm Chart and should not be added to it in the source repository.
During installation of custom chart, the Airflow chart will also be installed too.

You can extend the official Airflow chart by applying the following steps.

Create your custom Helm Chart
-----------------------------

First, you will need to create you own chart directory. You can do it by running the following command:

.. code-block:: bash

   helm create my-custom-chart


This command will create a directory called ``my-custom-chart`` with the following structure:

.. code-block:: none

   my-custom-chart/
   ├── .helmignore
   ├── Chart.yaml
   ├── values.yaml
   ├── charts/
   └── templates/
       └── tests/

Add Airflow Helm Chart as dependency
------------------------------------

Second, you will need to add the Airflow chart as dependency to the custom chart.
This will give you the ability to add your custom templates without the need to modify the Airflow chart itself.
In order to add the Airflow chart as a dependency (often called ``subcharts``) to your chart,
add the following lines to your ``Chart.yaml`` file:

.. code-block:: yaml
   :caption: Chart.yaml

   dependencies:
     - name: airflow
       version: 1.11.0
       repository: https://airflow.apache.org

.. note::

   Make sure you have already added the Airflow repo locally by running: ``helm repo add apache-airflow https://airflow.apache.org``.

.. tip::

   You can also use the name of the repo instead of the URL by replacing
   ``https://airflow.apache.org`` with ``"@apache-airflow"``.

Adding the Airflow chart as a dependency means that it will be deployed together with your custom chart.
You can disable the installation of Airflow by adding the ``condition`` field to the ``dependencies`` section
like in the example below:

.. code-block:: yaml
   :caption: Chart.yaml

   dependencies:
     - name: airflow
       version: 1.11.0
       repository: https://airflow.apache.org
       condition: airflow.enabled

This will check if the value of ``airflow.enabled`` inside your ``values.yaml`` is ``true``.
If it is, the Airflow chart will be deployed together with your custom chart.
Otherwise, only your templates will be deployed.

Download the Airflow Helm Chart
-------------------------------

Third, after you have specified the Airflow chart inside the ``dependencies`` section in ``Chart.yaml`` file,
you can download it by running the following command:

.. code-block:: bash

   helm dependency build

.. note::

   Make sure you are inside the directory which contains the ``Chart.yaml`` file.

The chart will be downloaded and saved inside the ``charts/`` directory.

Overriding default values
-------------------------

When you add a chart as a subchart to your chart,
you have the ability to override the default values of the subchart in your ``values.yaml``.
This is useful when your chart needs a specific configuration for your custom chart.
E.g. if you want that the Airflow chart be installed with the ``KubernetesExecutor``,
you can do it by adding the following section to your ``values.yaml``:

.. code-block:: yaml
   :caption: values.yaml

   airflow:
     executor: KubernetesExecutor
