Airflow Boilerplate

A complete development environment setup for working with Airflow, based on this Medium article. If you are interested in learning about the thoughts and processes behind this setup, do read the article. Otherwise, if you want to get hands-on immediately, you can skip it and just follow the instructions below to get started.

This boilerplate has more tools than was discussed in the article. In particular, it has the following things that were not discussed in the article:

A sample DAG
A sample plugin
A sample test for the plugin
A sample helper method, dags/common/stringcase.py, accessible in both dags/ and plugins/
A sample test for the helper method
A spark-conf/ that is included in the Docker build step, you can explore this on your own
A .pre-commit-config.yaml

Getting Started

Install docker and docker-compose at:

Clone this repo and cd into it:

git clone https://github.com/ninja-van/airflow-boilerplate.git && cd airflow-boilerplate

Create a virtualenv for this project. Feel free to choose your preferred way of managing Python virtual environments. I usually do it this way:

pip install virtualenv
virtualenv .venv

Activate the virtual environment:

source .venv/bin/activate

Install the requirements:

pip install -r requirements-airflow.txt
pip install -r requirements-dev.txt

Install the pre-commit hook:

pre-commit install

This will ensure for each commit, any file changes are gone through the linter and formatter. On top of that, tests are ran, too, to make sure that nothing is broken.

Setting up the Docker environment

If you only want the DB to be up because you will mostly work using PyCharm:

docker-compose -f docker/docker-compose.yml up -d airflow_initdb

If you want the whole suit of Airflow components to be up and running:

docker-compose -f docker/docker-compose.yml up -d

This brings up the Airflow postgres metadatabase, scheduler, and webserver.

To access the webserver, once the Docker container is up and healthy, go to localhost:8080. You can start playing around with the samples DAGs.

Setting up PyCharm

Ensure that your Project Interpreter is pointing to the correct virtual environment.

Mark both dags/ and plugins/ as source.

Run source env.sh on the terminal and copy the environment variables.

Add a new Run/Debug Configuration with the following parameters:

Name: <whatever_you_want>
Script path: <path_to_your_virtualenv_airflow_executable>
Parameters: test <dag_id> <task_id> <execution_date>
Environment variables: paste your env vars here

Add those environment variables to your test configuration (pytest in my case), so that you can just hit the run/debug button next to your test functions.

Generating a new fernet key

Included in this boilerplate is a pre-generated fernet key. There should not be any security concern here because after all you are meant to run this environment only locally. If you wish to have a new fernet key, you can follow these steps below.

Generate a fernet key:

python -c "from cryptography.fernet import Fernet; FERNET_KEY = Fernet.generate_key().decode(); print(FERNET_KEY)"

Copy that fernet key to clipboard. In env.sh, paste it here:

export AIRFLOW__CORE__FERNET_KEY=<YOUR_FERNET_KEY_HERE>

In airflow.cfg, paste it here:

fernet_key = <YOUR_FERNET_KEY_HERE>

Caveats

The PyPi packages are installed during build time instead of run time, to minimise the start-up time of our development environment. As a side-effect, if there is any new PyPi packages, the images need to be rebuilt. You can do so by passing the extra --build flag:
```
docker-compose -f docker/docker-compose.yml up -d --build
```
PyCharm cannot recognise custom plugins registered dynamically by Airflow, because IDE does static analysis and the custom plugins are registered dynamically during runtime.

Not related to the build environment, but rather how Airflow works - some of the configs (like rbac = True) you change in airflow.cfg might not be reflected immediately on runtime, because they are static configurations and are only evaluated once in the startup. To solve that problem, just restart your webserver:
```
docker-compose -f docker/docker-compose.yml restart airflow_webserver
```
Not related to the build environment, but rather how Airflow works - you cannot have a ; package/module in dags/ and plugins/ with the same name. This will likely give you a ModuleNotFoundError

Concluding tips

If you are only interested in just using your IDE, and you do not need the Airflow scheduler or webserver, run:
```
docker-compose -f docker/docker-compose.yml up -d airflow_initdb
```
To remove the examples from the Webserver, change the following line in the airflow.cfg:
```
load_examples = False
```
Notice that the docker-compose immediately picks up the changes in airflow.cfg.

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