How to monitor code changes / reload app automatically after errors?

[kennyhei]

Everything is working great with this project except that apparently gunicorn is not able to survive from e.g. coding errors. App crashes -> I fix the error -> code changes are not being monitored anymore and app does not reload. As a workaround I have to manually restart the web container.

Am I missing something here or could there be e.g. dev configuration for using python manage.py runserver?

[kennyhei]

Here's my fix unless better solution is provided 😄

1. I added new environment variable DOCKER_ENV to .env with value development
2. I added the variable to args for x-app in compose.yaml:

- "DOCKER_ENV=${DOCKER_ENV:-production}"

3. I removed last line from Dockerfile CMD [...]
4. I modified bin/docker-entrypoint-web as follows:

#!/usr/bin/env bash

set -e

# Always keep this here as it ensures your latest built assets make their way
# into your volume persisted public directory.
cp -r /public_collected /app

if [ "$DOCKER_ENV" = "development" ]; then
    exec python manage.py runserver 0.0.0.0:8000
else
    exec gunicorn -c python:config.gunicorn config.wsgi
fi

And then build image again. Obviously runserver is slower than gunicorn but at least now app reloads even after code errors.

UPDATE:

My previous solution will mess up the ./run pip3:install script. Here are my latest changes:

1. Add new environment variable DOCKER_ENV to .env with value development
2. In compose.yaml, add this to x-app (after volumes):

  command: >
    sh -c
    'if [ "$DOCKER_ENV" = "development" ]; then
      exec python manage.py runserver 0.0.0.0:8000
    else
      exec gunicorn -c python:config.gunicorn config.wsgi
    fi'

3. Remove last line from Dockerfile (CMD [...] )
4. Leave bin/docker-entrypoint-web as it is!

And you're done.

[nickjj]

That is one way to solve it. The concern there is not using the same app server in development vs production. That's why I tend to stick with gunicorn in all environments although it shouldn't be too bad.

I'm not aware of too many other options unless you had a wrapper process start gunicorn which always stays up and then if it detects gunicorn went down it would restart it. Basically a process monitor.