Yesterday I updated a Play Framework running on Heroku from version 2.2.x to 2.3.x. The process was mostly pain free. I updated some dependecies and did a couple of migration steps, no problems. Finally I ran sbt clean build to test my application. Testing when fine so I decided to deploy the new version.
I got the first error during the build process on heroku. The message was:
java.util.NoSuchElementException: key not found XXX
The missing element actually changed during subsequent builds on heroku. At first I thought it migth be a problem running on Java 6, so I updated to Java 7. The problem still existed. When I finally sat down to read all the output from Heroku, I discovered that Heroku does not run the sbt clean command before building the project. A quick google search told my how to run sbt clean on Heroku. All you have to do is set the environment variable SBT_CLEAN=true for your application. If you have the heroku toolbelt installed you can do this by running:
heroku config:set SBT_CLEAN=true
That’s it! Heroku will now run sbt clean before building your projects.