GitHub Actions

Getting started

Check out this quick guide. I recommend testing with a public repository as you go along with the guide. It’s very fast! ⚡️

Basics

• It’s a good idea to install this VSCode extension. At the very least, it can help lint the YAML files you write.
• You can test actions locally by using act, which essentially just uses the Docker API to do everything that GitHub would (but on your machine).

Manually running a workflow

• When authoring a workflow, consider using workflow_dispatch, which lets you manually trigger the workflow rather than waiting for an event like a push (reference, YAML reference):

on:
  push:
    branches: [main]

  # Allow manual triggering. Just leave this blank if you have no inputs.
  workflow_dispatch:

• Note that you don’t need the YML file to specify contents: write; it’s your user that needs write permissions. So if you don’t have the “Run workflow” button after adding workflow_dispatch, make sure you’re logged in as an admin of the repo.

Reference links

• All Docker-related GitHub actions: https://docs.docker.com/build/ci/github-actions/
• Workflows that I’ve written for my bot

Finding a usable tag from an action in the marketplace

Suppose you’re on a page like this: https://github.com/docker/login-action. You may see a “View on Marketplace” button:

Clicking that will bring you to a page with a version selector at the upper right which you can use to see which tags are available:

Alternatively, you can just go to the Releases page and click “Tags” on it, which results in a URL like this: https://github.com/docker/login-action/tags

Troubleshooting

Can’t build a Docker image through GitHub actions

If you can build locally, then perhaps you should try cloning the repo and trying to build in that fresh clone. It’s possible that a COPY . . command doesn’t have the same source to copy from.