Investigate building images via GitHub Actions and configuring Heroku to deploy from those images, rather than duplicate build steps across services

[hancush]

Background

tk

Proposal

tk

Deliverables

tk

Timeline

tk

[hancush]

On deck for spring. Potentially impacts local development, as well.

[fgregg]

For a personal project, I used the github container service to significantly speed up CI. It was a good experience!

By default, the "docker/build-push-action" looks for a Dockerfile in the root directory. If it finds it, it builds the image and pushes it to github's newish container service ghcr.io. It only does this on tagged commits.

https://github.com/fgregg/knoxville_utility_burden/blob/main/.github/workflows/publish_docker.yml

To do this currently, you need to Enable improved container support.

[fgregg]

For private repos, if we were pulling this from outside the GH universe, you would need to login with a github personal authentication token, but that's a secret we can set in Heroku's environment

[hancush]

From what I can tell, Heroku doesn't allow you to deploy apps from external container registries. You can either build your image on deploy from a Dockerfile co-located with the code (our current paradigm), or push your image/s to the Heroku container registry. One huge downside to the latter strategy is that we'd no longer get review apps, which have been hugely beneficial to our productivity.

[hancush]

Great pattern suggestion from @fgregg: Have a primary Dockerfile that builds the image for GitHub, then a Heroku Dockerfile that just inherits from the existing image FROM ghci.io/${REPOSITORY}/${IMAGE}.