From MozillaWiki
Jump to: navigation, search

If you are looking for the general documentation that used to live here, it has been moved into the Balrog repository, and a built version of it is available on Read The Docs.

This page will continue to host information about Balrog that doesn't make sense to put into the repository, such as meeting notes and things related to our hosted versions of Balrog.

Balrog is the software that runs the server side component of the update system used by Firefox and other Mozilla products. It is the successor to AUS (Application Update Service), which did not scale to our current needs nor allow us to adapt to more recent business requirements. Balrog helps us ship updates faster and with much more flexibility than we’ve had in the past.



Balrog admin interface is accessible at (vpn required).

The public interface that Firefox and other applications talk to is at Many older update domains are also served by Balrog, including,, and More details on these can be found on the Client Domains page.

Support & Escalation

If the issue may be visible to users, please make sure #moc is also notified. They can also assist with the notifications below.

RelEng is the first point of contact for issues. To contact them, follow the standard RelEng escalation path.

If RelEng is unable to correct the issue, they may escalate to CloudOps.

Monitoring & Metrics

Metrics from RDS, EC2, and Nginx are available in the Datadog Dashboard.

We aggregate exceptions from both the public apps and admin app to CloudOps' Sentry instance.

Change Notification

Changes made to Rules, Scheduled Rule Changes, Permissions, or the read-only flag of a Release will send e-mail notification to the balrog-db-changes mailing list. This serves us an alert system - if we see changes made that we weren't expecting, we can go investigate them.

ELB Logs

Public app

NOTE: These instructions were written before Amazon Athena existed. The next time we need to do such analysis, it's probably worth giving it a try. Other techniques may be better too - the instructions below are just something we've done in the past.

The ELB logs for the public-facing application are replicated to the balrog-us-west-2-elb-logs S3 bucket, located in us-west-2. Logs are rotated very quickly, and we end up with tens of thousands of separate files each day. Because of this, and the fact that S3 has a lot of overhead per-file, it can be tricky to do analysis on them. You're unlikely to be able to download the logs locally in any reasonable amount of time (ie, less than a day), but mounting them on an EC2 instance in us-west-2 should provide you with reasonably quick access. Here's an example:

  • Launch EC2 instance (you probably a compute-optimized one, and at least 100GB of storage).
  • Generate an access token for your CloudOps AWS account. If you don't have a CloudOps AWS account, talk to Ben Hearsum or Bensong Wong. Put the token in a plaintext file somewhere on the instance.
    • If you've chosen local storage, you'll probably need to format and mount volume.
  • Install s3fs by following the instructions on
  • Mount the bucket on your instance, eg:
s3fs balrog-us-west-2-elb-logs /media/bucket -o passwd_file=pw.txt
  • Do some broad grepping directly on the S3 logs, and store it in a local file. This should speed up subsequent queries. Eg:
grep '/Firefox/.*WINNT.*/release/' /media/bucket/AWSLogs/361527076523/elasticloadbalancing/us-west-2/2016/09/17/* | gzip > /media/ephemeral0/sept-17-winnt-release.txt.gz
  • Do additional queries on the new logfile.

Admin app

Nginx logs for the admin app are available (on a ~1 day time delay) in the "net-mozaws-prod-us-west-2-logging" S3 bucket. These logs are small enough that downloading and querying them locally is generally the most efficient thing to do.


Balrog uses the built-in RDS backups. The database in snapshotted nightly, and incremental backups are done throughout the day. If necessary, we have the ability to recover to within a 5 minute window. Database restoration is done by CloudOps, and they should be contacted immediately if needed.

Deploying Changes

Balrog's stage and production infrastructure is managed by the Cloud Operations team. This section describes how to go from a reviewed patch to deploying it in production. You should generally begin this process at least 1 hour before you want the new code live in production. This gives CloudOps plenty of time to respond to the request.

Is now a good time?

Before you deploy, consider whether or not it's an appropriate time to. Some factors to consider:

  • Are we in the middle of an important release such as a chemspill? If so, it's probably not a good time to deploy.
  • Is it Friday? You probably don't want to deploy on a Friday except in extreme circumstances.
  • Do you need to migrate any data? If you do, make sure you have time to do so right after deploying.
  • Do you have enough time to safely do a push? Most pushes take at most 60 minutes to complete after the stage push has been done. This time is mostly affected by how long it takes you to verify your changes in stage and production.

Schema Upgrades

If you need to do a schema change you must ensure that either the current production code can run with your schema change applied, or that your new code can run with the old schema. Code and schema changes cannot be done at the same instant, so you must be able to support one of these scenarios. Generally, additive changes (column or table additions) should do the schema change first, while destructive changes (column or table deletions) should do the schema change second. You can simulate the upgrade with your local Docker containers to verify which is right for you.

When you file the deployment bug (see below), include a note about the schema change in it. Something like:

This push requires a schema change that needs to be done _prior_ to the new code going out. That can be performed by running the Docker image with the "upgrade-db" command, with DBURI set.

bug 1295678 is an example of a push with a schema change.


The stage environment automatically deploys new code from the master branch of the Balrog repository (including any necessary schema changes). Before asking for a push, you should do some functional testing there. At the very least, you should do explicit testing of all the new code that would be included in the push. Eg: if you're changing the format of a blob, make sure that you can add a new blob of that type, and that the XML response looks correct. When you've completed testing take note of the "commit" on - you'll need it when filing the production push bug.

If you have schema changes you must also ensure that the existing deployed code will work with the new schema. To do this, CloudOps will downgrade the stage apps. You should do some routine testing (make some changes to some objects, try some update requests) to ensure that everything works. If you have any issues you CANNOT proceed to production.

Pushing to production

Pushing live requires CloudOps. For non-urgent pushes, please make sure you file the bug for them X hours in advance. For urgent pushes, file the bug immediately and escalate if no action is taken quickly. Either way, you must follow this procedure to push:

  1. Tag the repository with a "vX.Y" tag. Eg: "git tag -s vX.Y"
  2. Diff against the previous release tag. Eg: "git diff v2.24 v2.25"
    • Look for anything unexpected, or any schema changes. If schema changes are present, see the above section for instructions on handling them.
  3. Wait for CI jobs to complete. Unit tests must pass and a new Docker Image for the webapps and the Agent must be pushed to Dockerhub before you proceed.
  4. File a bug to have the new version pushed to production. Be sure to substitute the new version number, and commit SHA for the Docker image tags.
    • This bug should generally be filed at least a few hours in advance of the desired production push time to ensure that CloudOps has time to react to it.
    • Wednesdays are usually the best day to push to production, because they are generally free of release events. Unless you have a specific need to deploy on a different day, you should request the prod push for a Wednesday.
    • You should link any bugs being deployed is the "Blocks" field.
  5. Once the push has happened, verify that the code was pushed to production by checking the __version__ endpoints on the Admin and Public apps.
  6. Bump the in-repo version to the next available one to ensure the next push gets a new version.

Meeting Notes