Last updated August 02, 2024

Buildpacks are responsible for transforming deployed code into a slug, which can then be executed on a dyno. Buildpacks are composed of a set of scripts, and depending on the programming language, the scripts will retrieve dependencies, output generated assets or compiled code, and more. This output is assembled into a slug by the slug compiler.

Heroku’s support for Ruby, Python, Java, Clojure, Node.js, Scala, Go and PHP is implemented via a set of open source buildpacks.

Officially supported buildpacks

Heroku maintains a collection of officially supported buildpacks that are available by default to all Heroku apps during slug compilation.

By default, these buildpacks will be searched in this order until a match is detected and used to compile your app. If the build succeeds, the detected buildpack will be permanently set for future pushes to your application as if you had run heroku buildpacks:set manually as explained below.

Custom buildpacks can be used to support languages or frameworks that are not covered by Heroku’s officially supported buildpacks. For a list of known third-party buildpacks, see Using a third-party buildpack.

Setting a buildpack on an application

You can change the buildpack used by an application by setting the buildpack value. When the application is next pushed, the new buildpack will be used.

$ heroku buildpacks:set heroku/php
Buildpack set. Next release on random-app-1234 will use heroku/php.
Run `git push heroku master` to create a new release using this buildpack.

You may also specify a buildpack during app creation:

$ heroku create myapp --buildpack heroku/python

Setting a buildpack in app.json

The buildpack can be explicitly set in app.json so that applications created via Heroku buttons, Heroku CI or Review Apps can use custom buildpacks. Changing app.json won’t update the settings of existing apps, you will need to use the heroku buildpacks command instead.

Removing a buildpack from an app

You can easily remove a buildpack from an app:

$ heroku buildpacks:remove heroku/nodejs

Detection failure

If the configured buildpack cannot handle your application (as determined by its detection script), you will receive an error. For example, Heroku’s Ruby buildpack expects a Gemfile to be present in the root folder of an application to correctly identify its type, but if the buildpack of an application is set to heroku/ruby and no Gemfile is present, the application will fail to build.

-----> Using set buildpack heroku/nodejs
 !     Push rejected, failed to detect set buildpack heroku/nodejs

Using an official buildpack

If Heroku’s auto-detection of buildpacks is not sufficient, or if you need multiple buildpacks you can configure your app to run with one of the default buildpacks by executing a command such as this:

$ heroku buildpacks:set heroku/ruby
Buildpack set. Next release on random-app-1234 will use heroku/ruby.
Run `git push heroku master` to create a new release using this buildpack.

This example forces Heroku to use the latest release version of the official Ruby buildpack on your next deployment (and every deployment after unless you change it). Instead of heroku/ruby, you may use any of the other shorthand identifiers listed above in the table of official buildpacks.

Using a third-party buildpack

If Heroku’s official buildpacks don’t support your app’s requirements, check out the curated list of custom, third-party buildpacks in the Elements marketplace. You can also search through hundreds of custom buildpacks via the CLI. To search, run:

$ heroku buildpacks:search elixir
Buildpack        Category   Description
───────────────  ─────────  ───────────────────────────
hashnuke/elixir  languages  Heroku Buildpack for Elixir

$ heroku buildpacks:info hashnuke/elixir
description: Heroku Buildpack for Elixir
category:    languages
license:     MIT License
support:     https://github.com/HashNuke/heroku-buildpack-elixir/issues
source:      https://github.com/HashNuke/heroku-buildpack-elixir
readme:

$ heroku buildpacks:set hashnuke/elixir
Buildpack set. Next release on agile-plains-12843 will use hashnuke/elixir.
Run git push heroku master to create a new release using this buildpack.

You can specify the buildpack namespace/name or Git URL of a third-party buildpack when creating a new app:

$ heroku create myapp --buildpack https://github.com/some/buildpack.git

You can also do so for an existing app like so:

$ heroku buildpacks:set https://github.com/some/buildpack.git -a myapp

You can return to using your app’s default Heroku buildpack with the following command:

$ heroku buildpacks:clear

Buildpack references

Buildpack values can be set to any of:

• the short-form Buildpack Registry name (for published buildpacks), eg: heroku/python
• the URL of a Git repository, eg https://github.com/heroku/heroku-buildpack-nodejs.git
• a gzipped tarball URL

Using multiple buildpacks

There are many scenarios in which a single buildpack is not sufficient when building an application. Typical scenarios include database connection pooling using PgBouncer, or asset handling using a Node.js library in combination with a Ruby, Python or PHP application.

When this is the case, please follow our guide to Using Multiple Buildpacks for an App.

Creating a buildpack

If you’d like to use a language or framework not yet supported on Heroku you can create a custom buildpack. To get started, see the following articles:

• To learn about the structure of a buildpack, see Buildpack API.

Build manifest

If you would like to create a build manifest, which can be checked into source control and allows you to easily install packages, learn more about heroku.yml

Other compilation & deployment methods

• You can deploy Docker images directly to Heroku
• You can manually create and deploy a slug via the platform API.