PEX Recipes and Notes

PEX app in a container

If you want to use a PEX application in a container, you can get the smallest container footprint and the lowest latency application start-up by installing it with the venv Pex tool. First make sure you build the pex with --include-tools (or --venv), and then install it in the container like so:

COPY my.pex /my-app.pex
RUN PEX_TOOLS=1 /mp-app.pex venv --rm all --compile /my-app
ENTRYPOINT ["/mp-app/pex"]

The Pex venv tool will:

  1. Install the PEX as a traditional venv at /my-app with a script at /my-app/pex that runs just like the original PEX.

  2. Pre-compile all PEX Python code installed in the venv.

  3. Remove the original /my-app.pex as well as any temporary caches created by Pex in the PEX_ROOT, leaving just the newly installed and pre-compiled /my-app venv.

PEX-aware application

If your code benefits from knowing whether it is running from within a PEX or not, you can inspect the PEX environment variable. If it is set, it will be the absolute path of the PEX your code is running in. Normally this will be a PEX zip file, but it could be a directory path if the PEX was built with a --layout of packed or loose.

Gunicorn and PEX

Normally, to run a wsgi-compatible application with Gunicorn, you’d just point Gunicorn at your application, tell Gunicorn how to run it, and you’re ready to go - but if your application is shipping as a PEX file, you’ll have to bundle Gunicorn as a dependency and set Gunicorn as your entry point. Gunicorn can’t enter a PEX file to retrieve the wsgi instance, but that doesn’t prevent the PEX from invoking Gunicorn.

This retains the benefit of zero pip install’s to run your service, but it requires a bit more setup as you must ensure Gunicorn is packaged as a dependency. The following snippets assume Flask as the wsgi framework, Django setup should be similar:

$ pex flask gunicorn myapp -c gunicorn -o ~/service.pex

Once your pex file is created, you need to make sure to pass your wsgi app instance name to the CLI at runtime for Gunicorn to know how to hook into it, configuration can be passed in the same way:

$ service.pex myapp:appinstance -c /path/to/

And there you have it, a fully portable python web service.

PEX and Proxy settings

While building pex files, you may need to fetch dependencies through a proxy. The easiest way is to use pex cli with the requests extra and environment variables. Following are the steps to do just that:

  1. Install pex with requests

$ pip install pex[requests]
  1. Set the environment variables

$ # Hopefully your proxy supports https! If not, you can export HTTP_PROXY:
$ # export HTTP_PROXY='http://user:pass@address:port'
$ export HTTPS_PROXY='https://user:pass@address:port'
  1. Now you can test by running

$ pex -v pex

For more information on the requests module support for proxies via environment variables, see the official documentation here: