Balrog in Release Promotion


Balrog is Mozilla’s update server. It is responsible for delivering newer versions of Firefox to existing Firefox installations. If you are not already, it would be useful to be familiar with Balrog’s core concepts before continuing with this doc. You can find that information on Balrog’s official documentation.

The basic interactions that Release Promotion has with Balrog are as follows:

  1. Submit new release metadata to Balrog with a number of balrog tasks and the release-balrog-submit-toplevel task.

  2. Update test channels to point at the new release in the release-balrog-submit-toplevel task.

  3. Verify the new release updates with release-update-verify and release-final-verify tasks.

  4. Schedule the new release to be shipped in the release-balrog-scheduling task.

Submit New Release Metadata

Balrog requires many different pieces of information before it can ship updates. Most of this information revolves around update file (MAR) metadata (hash, filesize, target platform, target locale). This information is submitted by balrog tasks.

We also submit some more general information about releases (version number, MAR url templates, release name, etc.) as part of the release-balrog-submit-toplevel task.

All balrog submission is done by balrogscript workers, and happens in the promote phase.

Update Test Channels

Balrog has “test” channels that we use to allow verification of new release updates prior to shipping. The release-balrog-submit-toplevel task is responsible for updating these test channels whenever we prepare a new release. This happens in the promote phase.

Verify the Release

Once a release is live on a test channel release-update-verify begins and performs same sanity checks. This happens in the promote phase.

After a release has been pushed to cdns, release-final-verify runs and performs some additional checks. This happens in the push phase.

Schedule Shipping

When we’re ready to ship a release we need to let Balrog know about it by scheduling a change to the appropriate Balrog rule. If release_eta is set it will be used as the ship date and time. If not, the release will be scheduled for shipping 5 minutes in the future. In either case, signoff will need to be done in Balrog by multiple parties before the release is actually made live.

This step is done by the release-balrog-scheduling task in the ship phase.

secondary tasks

You may have noticed secondary variants of the release-balrog-submit-toplevel, release-update-verify, release-final-verify, and release-balrog-scheduling tasks. These fulfill the same function as their primary counterparts, but for the “beta” update channel. They are only used when we build Release Candidates.