UpdateGeneration

Update generation

One of the key features of Firefox is the update system that allows Mozilla to push out bug fixes and new features to users automatically.

Current processes

Currently we use two different sets of processes and tools to generate updates for nightly updates and releases.

Nightly updates

We make updates available for official nightly builds for all current code branches. This helps ensure that our nightly testers are always running the most recent code with the least possible effort. These updates are offered on the 'nightly' update channel.

Both complete and partial updates are offered. If the user is running the most recent previous nightly build, the partial update is served. Otherwise, the complete update is always served. This greatly simplifies/expedites the update generation matrix.

Steps for nightly update generation (3.5 branch and earlier):

• nightly builders generate complete MAR using Makefile
• upload complete MAR to staging along with build
• upload complete snippet to AUS2 server
• prometheus-vm runs cron script every 5 minutes (patch-packager-cron.sh) that calls patch-packager.pl. In the simplest terms, this script does the following:
  1. Read in all of the available builds.
  2. Compute all of the patches we could offer.
  3. Read in all of the offered patches.
  4. Compute which patches we aren't offering which we could.
  5. Create all of the patches we could offer.
  6. Upload them.

As of Firefox 3.6, we've stopped funneling all partial updates through prometheus-vm in favor of generating the partial updates directly on the builders. This gives us much quicker turnaround on update generation.

Steps for nightly update generation (3.6 branch, project branches, and later):

• nightly builder generate complete MAR using Makefile
• nightly builder downloads the previous complete MAR from the latest dir on the staging server
• nightly builder generates partial MAR containing the differences between the two complete MARS using Makefile
• nightly builder generates snippets for both the complete and partial updates
• nightly builder uploads snippets directly to the AUS2 server

What the Makefiles do, or How to make your own updates

The build system generates update MAR files using the Makefile and associated scripts in the tools/update-packaging source directory. The Makefile isn't strictly necessary though. It simply formats the calls to the other scripts based on values stored in environment variables, making it easier to automate update generation.

Creating a complete MAR

This script used to generate a complete MAR file is make_full_update.sh.

Creating a partial MAR

This script used to generate a partial MAR file is make_incremental_update.sh.

Updates for security releases

We create both partial and complete updates for security releases (aka as 'dot' releases, e.g. 3.5.x). These updates are only ever served to users on the same product branch.

Legitimate partial updates, i.e. binary diffs, are generated for migrating users from the previous security release to the new security release, e.g. 3.5.1->3.5.2. Complete mars are served to those users on older security releases, e.g. 3.5->3.5.2. Because the updater checks for partial updates before complete updates, the update system serves the complete update for a security release as a partial update to all users on previous security releases. This avoids presenting the user with a failed check for a partial update that, while harmless, might be confusing.

Steps for security release update generation:

• partial MARs and AUS configuration data are generated using the patcher2 tool: http://mxr.mozilla.org/mozilla/source/tools/patcher/
• a release engineer puts the appropriate URLs, version numbers, and build IDs into the patcher configuration file: http://mxr.mozilla.org/mozilla/source/tools/patcher-configs/
• patcher downloads the complete MARs, creates partial diffs (using mbsdiff), and generates partial MAR files as well as AUS configuration files ("snippet" files).
• patcher generates both production ("release") and testing ("releasetest") snippets, release snippets point to bouncer while releasetest snippets point to stage.
• partial MAR files are copied to the candidates directory, and the releasetest snippets are loaded into AUS.

Which machines do what

Machine Name	Function
any build slave	build generation complete patch(MAR) generation partial patch(MAR) generation (3.6+) XML snippet generation (3.6+)
prometheus-vm	partial patch(MAR) generation (3.5) XML snippet generation (3.5)
aus2-staging.mozilla.com	store/serve snippets

Staging environment for nightly updates

The staging environment for nightly updates consists of two machines:

• staging-nightly-updates: this machine mirrors prometheus-vm in production, running the patch-packager scripts to generate partial mars based on update snippets published to...
• staging-stage: used like stage.m.o in production to house builds and mars, but also holds the aus2 snippets used in update generation and publishing

Common problems and resolutions with updates in the staging environment

Downloaded MAR file doesn't match the hash in the snippet

This can happen when two successful "nightly" builds start in the same hour (this shouldn't ever happen in production FWIW). The result is two different snippet files for two different mars, but only one mar in the corresponding build dir on staging-stage (these dirnames are only accurate down to the hour).

Removing the orphaned snippet should fix things up.