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Heroku Cloud Native sbt Buildpack

CI

Heroku's official Cloud Native Buildpack for sbt usage in Scala applications.

How it works

The buildpack will detect if your application requires sbt if any one of the following file patterns match:

  • project/build.properties
  • project/*.scala
  • *.sbt
  • .sbt/*.scala

Step 1: Download sbt

An sbt wrapper script is written into its own layer that will contain the sbt build tooling. This wrapper script then executes to download the sbt version specified in your project/build.properties file.

Step 2: Run sbt

By default, the sbt command used to build the application is sbt compile stage. Applications that require customizations to this process to build successfully should refer to the Customizing section of this document.

Customizing

This buildpack exposes the following configurable settings. The order they appear in the table indicates their precedence.

For example, if your application contains:

  • a system.properties file with the sbt.project property set
  • and the environment variable SBT_PROJECT is set

Then the value from system.properties will be used.

Configure a sbt subproject build

When this setting is configured, the default build tasks will be prepended with the supplied project name. E.g.; the default compile and stage tasks would become {subproject}/compile and {subproject}/stage.

From Path Name
Java property file system.properties sbt.project
Environment SBT_PROJECT

Specify tasks to execute before building

This setting will prepend the supplied tasks to the list of tasks to run during the build. These must be supplied as a string of space-separated task names. E.g.; a value of task1 task2 would cause the build step to be invoked with sbt task1 task2 compile stage.

From Path Name
Java property file system.properties sbt.pre-tasks
Environment SBT_PRE_TASKS

Specify which build tasks to use

This setting will override the default build tasks of compile and stage. These must be supplied as a string of space-separated task names. E.g.; a value of mybuild would cause the build step to be invoked with sbt mybuild.

From Path Name
Java property file system.properties sbt.tasks
Environment SBT_TASKS

Cleaning the project before build

This setting will prepend a clean task to before all other tasks to run during the build. This must be supplied as a value of either true or false. E.g.; setting this value to true would cause the build step to be invoked with sbt clean compile stage.

From Path Name
Java property file system.properties sbt.clean
Environment SBT_CLEAN

Making sbt available at launch

By default, the sbt executable as well as its caches are only available during the build process. If you need sbt to launch your application you can configure this setting with a value of true.

From Path Name
Java property file system.properties sbt.available-at-launch
Environment SBT_AVAILABLE_AT_LAUNCH

Adding custom sbt options

If the SBT_OPTS environment variable is defined when sbt starts, its content are passed as command line arguments to the JVM running sbt.

If a file named .sbtopts exists, its content is appended to SBT_OPTS.

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"
From Path Name
Environment SBT_OPTS
Options file .sbtopts

Build Plan

Requires

  • jdk: To compile Java sources a JDK is required. It can be provided by the heroku/jvm (Source, Readme) buildpack.
  • jvm-application: This is not a strict requirement of the buildpack. Requiring jvm-application ensures that this buildpack can be used even when no other buildpack requires jvm-application.

Provides

  • jvm-application: Allows other buildpacks to depend on a compiled JVM application.

License

See LICENSE file.