Heroku-16 Stack

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Last updated October 24, 2026

The Heroku-16 stack reached end-of-life on May 1st, 2021. Please upgrade to a newer stack as soon as possible. See the Heroku-16 End-Of-Life FAQ for more details.

This article describes the Heroku-16 stack, based on Ubuntu 16.04. What is a stack?

What’s new

We’ve made the following changes from the Cedar-14 stack to the Heroku-16 stack:

  • Heroku-16 is much smaller, with a Docker image of 465 MB (vs 1.35 GB for Cedar-14).
  • Improved support for compiling native Ruby and Python packages
  • The JDK is installed by the Java/JVM buildpack. If you have an app that uses Java, but not the Java buildpack (e.g., jython or a Java Bridge), you’ll have to set the JVM buildpack on your app (instructions are listed below).
  • The HEROKU_ namespace is reserved for config vars set by the Heroku platform in order to offer functionality. If you have created HEROKU_ config vars, we suggest you change them when upgrading to Heroku-16, in order to avoid config var conflicts.

Support period

Heroku-16 is based on Ubuntu 16.04, and so reached end-of-life on May 1st, 2021. See the Heroku-16 End-Of-Life FAQ for more details.

Using Heroku-16

It is no longer possible to create new Heroku-16 apps, or to switch an existing app’s stack to Heroku-16. Please use a supported stack instead.