minimal-python-api

Using Twitter's Pants build tool, creating a minimal docker image using a compiled PEX

What is pants?

Pants (Python Ant) is a build to designed by Twitter to help with managing Polyglot Monorepos. It can be used to help manage inter-code dependencies, build and compile different languages (scala, python, go, etc.) and build distributions. For more information on Pants, check them out at https://www.pantsbuild.org/index.html

Then what is a PEX?

A PEX (Python EXecutable) are executable python environments as outlined in PEP441. They are created in the spirit of virtualenvs, but are much more lightweight. The PEX enables the developer to simply deploy a python application simply by copying the *.pex file and executing it.

Instructions

I will work on better instructions, these are just initial notes. If this gains some traction, I'll do a more hands on tutorial as I better understand Pants myself.

Pants build process

//TODO

Building the PEX

In the root directory run

./pants binary src/main/python/api/src:api

This will create the PEX file in the dist directory

Building packages

Creating a tarball

In the root directory run

./pants setup-py src/main/pyton/api:lib 

This will create a tarball within the dist directory.

Creating a wheel

Create a tarball and then run pip wheel <tarball_name> against the file to create the wheel.

Alternatively to create a python wheel file as well you'll need to run

./pants setup-py src/main/python/api:lib --setup-py-run="bdist_wheel --dist-dir=<YOUR FULL DIRECTORY PATH>/pantstest/dist"

This will create a wheel file in your dist folder. If you don't specify the full path, the wheel will be inside the package directory in your dist folder. For example, if you create the api wheel file without specifying the --dist-dir, the wheel file will be ~/minimal-python-api/dist/api-0.1.0/dist/example_api-0.1.0-py2-none-any.whl.

Testing

Unit tests

//TODO

Coverage

//TODO

Creating the Docker image

For the docker image I'm simply using a Python Alpine image. NOTE. make sure the python version you use for the alpine image matches what's in your pants.ini file. Copy the PEX into the container and run it. It's that simple. I'll work on gathering size comparisons of deploying the Python app via a wheel vs. the PEX. In my experience, this is the simpliest (in terms of the Dockerfile) and smallest Docker Python app I've made.

Contributions

If I've made some mistake or you would like me to go over some other build processes, please submit an issue and I'll try to help as much as I can.