At Pulumi, we do all of our development on GitHub, with a workflow built around topic branches. When a developer wants to make a change, they push a branch to GitHub, open a pull request and (in theory) once it’s merged, delete the branch. In practice, we’ll often forget to delete the topic branch (I’m probably the worst offender), which means we end up having topic branches linger on our main repository until they are explicitly cleaned up. While it’s a lot of fun to go a click through the GitHub UI from time to time, deleting merged branches, it’s even more fun to build automation to do this for us. Since GitHub has a rich set of webhooks and Pulumi makes it easy to write serverless functions, it felt like it would be natural to use Pulumi to write a hook that would clean up branches after a pull request got merged. In addition, Pulumi lets us leverage real programming languages to build abstractions, which means we can build a simple framework that hides much of the ceremony behind defining a hook and lets us focus on the core logic of our hook, without worrying about how it is deployed and managed.