Change effective on 18 November 2015
The labs feature Dyno Metadata has been released. This gives processes running in a dyno easy access to information about the dyno, the app and the environment. Examples of available dyno metadata include details about the release, dyno size, application name as well as the unique identifier for the particular running dyno.
You can enable this by running:
heroku labs:enable runtime-dyno-metadata -a <app name>
In addition to this, from now on, it is not recommended that you set HEROKU_* environment variables on your application as it runs the risk of conflicting with these changes.
See this Dev Center article for more information.