Building brntn.me when another Github Repo changes using Github Actions

Note: my website no longer builds using this method, but triggering a GitHub Actions build from a different build is still a useful ability.

The repository that builds my website (sesh/brntn.me) pulls in content from other repositories. I wanted my site to automatically rebuild any time one of those other repositories is updated.

There's a few examples of how to do this out there, but I wanted to jot down my quick and dirty solution in case it's helpful for anyone else.

We're going to be working with two different repositories here, so lets name them to make things simpler:

• parent-repo is the main repository. It should already have a Github Action that builds the site. In my case this is the repository for this website.
• child-repo is a second repository that should trigger the build of parent-repo on change.

Step One: Add repository_dispatch to your build Github Action for parent-repo

In the on block of the Github Action that builds your parent project add a new repository_dispatch block. The repository_dispatch allows calls to the Github API to trigger your action. The types list is a list of dispatch types that will be used as triggers, in our case, we're going to add a single build type (we'll use this later).

on:
  repository_dispatch:
    types:
      - build

Step Two: Generate a Personal Access Token with repo permissions

To trigger the build you'll need a Personal Access token that has the repo set of scopes. You can create this from the Developer Settings section of your Github settings.

Once created, copy this and keep it safe.

Step Three: Add the secret to child-repo

In the Secrets section of the child-repo settings add the token that you just generated as a Repository Secret. I've named mine NOTIFY_TOKEN (you'll need this in the next step).

Step Four: Add the Notify action to child-repo

The final step is to add a new action to your child-repo that triggers the build. This action uses the NOTIFY_TOKEN created above. You'll need to manually update the action with the parent-repo name (see placeholder below).

For my projects I've put this in .github/workflows/notify.yml:

name: Trigger rebuild of parent repo
on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]
  workflow_dispatch:

jobs:
  notify:
    runs-on: ubuntu-20.04
    container: alpine/httpie
    steps:
      - name: Notify parent repo
        run: http post https://api.github.com/repos/<<YOUR_PARENT_REPO>>/dispatches "Authorization:token ${{ secrets.NOTIFY_TOKEN }}" event_type=build --ignore-stdin

And that's it! When your child-repo actions run (and we have it set to run on all pushes) it will trigger a build in the parent repo.