Buildpack: Scala

This is a Buildpack for Scala apps. It uses sbt 0.11.0+.

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.

$ scalingo create scala-app

$ git push scalingo master
...
-----> Scala app detected
-----> Building app with sbt
-----> Running: sbt compile stage

The buildpack will detect your app as Scala if it has the project/build.properties and either .sbt or .scala based build config. It vendors a version of sbt and your popluated .ivy/cache into your container. The .ivy2 directory will be cached between builds to allow for faster build times.

Documentation

For more information about using Scala and buildpacks on Scalingo, see these articles:

Scalingo's Scala Support

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:

$ scalingo env-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:

$ scalingo env-set SBT_CLEAN=true
SBT_CLEAN has been set to true.

All subsequent deploys will use the clean task. To remove the clean task, unset SBT_CLEAN:

$ scalingo env-unset SBT_CLEAN
SBT_CLEAN has been unset.

Development

To use this buildpack, fork it on Github. Push up changes to your fork, then create a test app with --buildpack <your-github-url> and push to it.

For example, to reduce your container size by not including the .ivy2/cache, you could add the following.

for DIR in $CACHED_DIRS ; do
rm -rf $CACHE_DIR/$DIR
mkdir -p $CACHE_DIR/$DIR
cp -r $DIR/.  $CACHE_DIR/$DIR
# The following 2 lines are what you would add
echo "-----> Dropping ivy cache from the container"
rm -rf $SBT_USER_HOME/.ivy2

Note: You will need to have your build copy the necessary jars to run your application to a place that will remain included with the container.