Hunting the Shmoo

Taskcluster Github is the Taskcluster service responsible for kick starting tasks on Github repositories. At a high level:

1. You install a Taskcluster app from the Github marketplace.
2. This app sends webhooks to the Github service.
3. Upon receiving a webhook, the Github service processes your repository’s .taskcluster.yml file.
4. The Github service schedules tasks (if any) and updates the Github checks suite, or comments on your push / pull-request if there is an error.

While the service itself is relatively simple, testing it locally can be a pain! One approach might be to try and synthesize Github’s webhook events, and then intercept the network requests that the Github service makes in response. But this is tricky to do, and without actually seeing the results in a proper Github repo, it’s hard to be sure that your changes are working as intended.

Ideally you would have a real repo, with a development version of the app listed in the Github Marketplace, hooked up to a Taskcluster Github service running on your local machine. This way you could trigger webhooks by performing real actions in your repo (such as opening a pull-request). Better yet, you could see exactly how your Github service changes react!

Thanks to a lot of great work from Yarik, this is easier than ever and is all documented (or linked to) from this page. If you are already familiar with Taskcluster development, or enjoy figuring things out yourself, you may wish to skip this post and read the docs instead. But if you are a Taskcluster newbie, and would appreciate some hand holding, follow along for a step by step tutorial on how to work on and test Taskcluster Github!