Heroku Buildpack Flutter Light 🪶

Build Flutter Web projects on Heroku. A configurable Buildpack with a light footprint. Designed to be easily paired with other Buildpacks and integrated into existing projects.

Why Heroku Buildpack Flutter Light?

This Buildpack was originally forked from Diego Zepeda's Heroku Buildpack Flutter. After testing, we realized that we needed to make different architectural tradeoffs than the original package.

The scope of our Heroku Buildpack Flutter Light is smaller. Unlike the original package, it is not concerned with serving the compiled files. It tests and compiles them but leaves serving them via HTTP to other Buildpacks that are better suited for that purpose (that includes a very straightforward integration with Heroku's heroku-buildpack-static).

This means that the Buildpack is able to deploy only the compiled files, stripping Flutter SDK, Dart SDK, and all other dependencies. That in turn makes the deploys much faster and less likely to hit Heroku's Slug size limit of 500 MB (in our tests we went from being above the limit to having slugs smaller than 10 MB).

Other key improvements include the Heroku CI integration and the ability to configure the project structure (which includes support for repositories where the Flutter project isn't located directly in the root directory).

Features

✅ Light footprint (deploys only the compiled files, stripping all sources, tools, and dependencies)
✅ Configurable directory structure
✅ Heroku CI integration
✅ Caching of dependencies (like Flutter, Dart, and pub.dev packages) between builds
✅ Works well with heroku-buildpack-static and other Buildpacks

Instalation

With heroku-buildpack-static (recommended)

Simply add the following two Buildpacks in your app configuration (in this order):

1. ee/heroku-buildpack-flutter-light
2. heroku-community/static

You can do this using the web interface (in the "Settings" tab) or with the heroku buildpacks:set command.

After deploying you should see your Flutter Web application. You can optionally customize the way the application is built and deployed using Heroku Buildpack Flutter Light's options and heroku-buidlpack-static's configuration. We strongly recommend pinning a specific Flutter version with the FLUTTER_VERSION config variable.

With a different server-side technology (advanced)

If your Flutter application is a part of a bigger project that already has its way of serving static files (for example with Node, Python, PHP, or Ruby), you can easily reuse it.

Add ee/heroku-buildpack-flutter-light to your Buildpacks, set FLUTTER_SOURCE_DIR to the directory (within your repository) where the Flutter project is located, and FLUTTER_DEPLOY_DIR to where the compiled application should be placed (i.e., a directory that your framework uses to serve static files).

Heroku CI integration

The Buildpack can be easily integrated with Heroku's Continuous Integration service (Heroku CI) to automatically run linters and tests.

Use the following steps:

1. Create a Heroku pipleine
2. Enable Heroku CI in the pipeline's configuration
3. Create an app.json file in the root of your repository

The app.json file should contain the app configuration, including the testing command that should be run by Heroku CI. All app.json options can be found in Heroku's app.json documentation. What follows is a very minimalistic (but working) app.json that runs Dart's built-in analyzer and your project's Flutter tests:

{
  "environments": {
    "test": {
      "scripts": {
        "test": "flutter analyze && flutter test"
      }
    }
  },
  "buildpacks": [
    {
      "url": "ee/heroku-buildpack-flutter-light"
    }
  ],
}

Alternatively, for repositories where the Flutter project is not located in the root of the repository, the following configuration can be used (where flutter-directory is the location of the Flutter project):

{
  "environments": {
    "test": {
      "scripts": {
        "test": "cd flutter-directory && flutter analyze && flutter test"
      }
    }
  },
  "buildpacks": [
    {
      "url": "ee/heroku-buildpack-flutter-light"
    }
  ],
  "env": {
    "FLUTTER_SOURCE_DIR": "flutter-directory"
  }
}

During tests, all your project's dependencies are present (including the Dart SDK, Flutter SDK, pub.dev requirements, and command-line tools), so you can use them when specifying the testing command.

Options

Optionally, you can use config variables to customize the Buildpack's behavior:

Variable	Default	Description
FLUTTER_CLEANUP	true	Whether to remove sources, tools, and dependencies before deployment
FLUTTER_VERSION	Last version in stable channel.	Flutter version used to compile the project. You can use any tag in the the official Flutter repository.
FLUTTER_BUILD	flutter build web --release --quiet	The command used to build the project
FLUTTER_SOURCE_DIR	/	The folder in your repository where the Flutter project is kept
FLUTTER_DEPLOY_DIR	public_html	The folder where the compiled app should be placed