We do not recommend tracking master branch for your Discourse instance, because master branch is usually bleeding edge or unstable. In this guide we’ll describe how to change tracking branch for your Discourse instance to tests-passed. Let’s get started!

Open configuration file app.yml. From console, run these commands:

cd /var/discourse
git pull
nano containers/app.yml

Configuration file will open in nano editor. Search for version (with Ctrl+W) in the file:

params:
  ## Which Git revision should this container use?
  version: HEAD

Replace HEAD with tests-passed:

params:
  ## Which Git revision should this container use?
  version: tests-passed

After completing your edits, press Ctrl+O then Enter to save and Ctrl+X to exit.

Rebuild the container:

git pull
./launcher rebuild app

That’s it! Your Discourse instance is tracking tests-passed branch now!

Source: https://meta.discourse.org/t/change-tracking-branch-for-your-discourse-instance/17014