Getting your SBT-built Java project onto Heroku

I love Heroku for quickly deploying and testing your applications. The free usage tier makes it no cost for simple applications, and the Git Push To Deploy mechanism is a great way to test your build environment isn’t using cached resources.

If you’ve got a DropWizard 0.7.x service or similar built using SBT 0.13.x, and you deploy it to Heroku you may encounter the following error message:-

[error] Not a valid command: stage (similar: last-grep, set, last)
[error] Not a valid project ID: stage
[error] Expected ':' (if selecting a configuration)
[error] Not a valid key: stage (similar: state, target, tags)

The fix to this is to use the SBT Native Packager.

At the bottom of your ./project/plugins.sbt file, add

addSbtPlugin("com.typesafe.sbt" % "sbt-native-packager" % "0.8.0")

In your ./build.sbt file, add at the top

import NativePackagerKeys._
 
packageArchetype.java_application

and change your ./Procfile to be

web target/universal/stage/bin/**your_project_name** -Ddw.server.connector.port=$PORT server config/local.yml

with your ./config/local.yml file looking something like:-

server:
  type: simple
  applicationContextPath: /
  adminContextPath: /admin
  connector:
    type: http
    port: 8080

This configuration binds the Admin and normal serving ports together because Heroku only allows you to bind to the Heroku-specified $PORT.

Push using Git and you should be up and running. (This is especially useful if you’re using an automated build tool such as Jenkins).