heroku-buildpack-bun

Heroku buildpack for Bun.

Fork of jetthoughts/heroku-buildpack-bun, which is itself copied from chibat/heroku-buildpack-deno.

Why this fork

Upstream doesn't support pinning a specific Bun version — it always installs the latest and runs bun upgrade. This fork reads .bun-version and installs that exact version, which matters when a newer Bun release has a regression you need to avoid.

Usage

Add the buildpack to your app:

heroku buildpacks:add https://github.com/devjah/heroku-buildpack-bun

Pin a Bun version by writing it to .bun-version in your repo root:

1.0.18

The buildpack also requires a bun.lockb in the repo to detect the app as a Bun app.

On every build it runs bun install --ignore-scripts (arbitrary postinstall scripts from transitive dependencies are not executed).

Supported stacks

Stack-agnostic — tested on heroku-22. Should work on heroku-24 (Bun requires glibc ≥ 2.28; heroku-24 ships glibc 2.39).

Caveats

• Heroku's Linux kernel doesn't support io_uring, which Bun uses for Bun.write(). Use node:fs.writeFile() instead.
• Switching .bun-version wipes the cached Bun binary and reinstalls, so the first build after a version bump is slightly slower.