Github Actions

https://docs.github.com/actions

Github Actions are open-ended workflows you can run from repositories. A common use case is CICD.

Most of the minutiae is in here: https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions

Tips and Tricks

Triggering workflows based on subdirectory changes

You can use on.push.paths and associated keywords to filter on changes within a particular path. You can also use path-ignore, which would be for changes anywhere except an ignored path.

You must pay attention to glob patterns if you want to correctly match file paths to patterns. For example, if you only want to run tests when the sub/ folder has changed, no matter how deeply nested the files, you need to match against sub/**.

on:
  push:
    paths:
      - 'sub/**'

It also seems important to use single quotes and not double quotes. I haven't confirmed why but I suspect it's a yaml thing.

Workflows

Triggers

Workflow triggers begin with on in the yaml file. It can be as simple as on: push or can be more complex, such as triggering on particular branch PRs. The example below would trigger on pushes to main and on pull requests targeting main.

on:
  push:
    branches: main
  pull_request:
    branches: main

Triggering jobs from other jobs

Use jobs.<job_id>.needs to have job b run only after the success of job a.

jobs:
  test:

  deploy:
    needs: test

Triggering workflows from other workflows

Use on: workflow_run. The example below runs every time the 'Run Tests' workflow completes regardless of success or failure.

on:
  workflow_run:
    workflows:
      - Run Tests
    types:
      - completed

To run a workflow conditioned on the success of the previous workflow, checking the previous workflow's conclusion outcome,

on:
  workflow_run:
    workflows:
      - Build
    types:
      - completed

jobs:
  on-success:
    runs-on: ubuntu-latest
    if: ${{ github.event.workflow_run.conclusion == 'success' }}
    steps:
      - run: echo 'The triggering workflow passed'
  on-failure:
    runs-on: ubuntu-latest
    if: ${{ github.event.workflow_run.conclusion == 'failure' }}
    steps:
      - run: echo 'The triggering workflow failed'