Heroku Buildpack for Scala 
This is the official Heroku buildpack for Scala apps.
How it works
The buildpack will detect your app as Scala if it has a project/build.properties file and either a .sbt or .scala based build config (for example, a build.sbt file). It vendors a version of sbt into your slug (if you are not using sbt-native-packager, it also includes your popluated .ivy/cache in the slug). The .ivy2 directory will be cached between builds to allow for faster build times.
It is strongly recommended that you use sbt-native-packager with this buildpack instead of sbt-start-script. The latter is deprecated, and will result in exessively large slug sizes.
Documentation
For more information about using Scala and buildpacks on Heroku, see these articles:
- Heroku's Scala Support
- Play Documentation: Deploying to Heroku
- Customizing the JDK
- Running a Remote sbt Console for a Scala or Play Application
- Using Node.js to perform JavaScript optimization for Play and Scala applications
- Reducing the Slug Size of Play 2.x Applications
Examples
There are a number of example applications that demonstrate various ways of configuring a project for use on Heroku. Here are a few:
Customizing
This buildpack uses sbt-extras to run sbt.
In this way, the execution of sbt can be customized either by setting
the SBT_OPTS config variable, or by creating a .sbtopts file in the
root directory of your project. When passing options to the underlying
sbt JVM, you must prefix them with -J. Thus, setting stack size for
the compile process would look like this:
$ heroku config:set SBT_OPTS="-J-Xss4m"
Running additional tasks before the build
Sometimes, it might be necessary to run additional sbt tasks before a build and deployment (for example, database migrations). Ideally, the tasks should be interdependent such that these tasks run automatically as pre-requisities to compile stage, but sometimes this might not be the case. To add any additional tasks, set the environment variable SBT_PRE_TASKS to a list of tasks that should be executed. If the following is set:
SBT_PRE_TASKS=flyway:migrate info
Then, the following command will be run for build:
sbt flyway:migrate info compile stage
Clean builds
In some cases, builds need to clean artifacts before compiling. If a clean build is necessary, configure builds to perform clean by setting SBT_CLEAN=true:
$ heroku config:set SBT_CLEAN=true
Setting config vars and restarting example-app... done, v17
SBT_CLEAN: true
All subsequent deploys will use the clean task. To remove the clean task, unset SBT_CLEAN:
$ heroku config:unset SBT_CLEAN
Unsetting SBT_CLEAN and restarting example-app... done, v18
Development
To make changes to this buildpack, fork it on Github. Push up changes to your fork, then create a new Heroku app to test it, or configure an existing app to use your buildpack:
# Create a new Heroku app that uses your buildpack
heroku create --buildpack <your-github-url>
# Configure an existing Heroku app to use your buildpack
heroku buildpacks:set <your-github-url>
# You can also use a git branch!
heroku buildpacks:set <your-github-url>#your-branch
License
Licensed under the MIT License. See LICENSE file.