The document describes Chrome's release cycle, which aims for predictable, regular releases by adopting an overlapping development model. Key aspects include releasing every 6 weeks on 3 channels, addressing all work on a central trunk before branching for stabilization, and controlling scope by disabling unfinished features at branch points. This approach improved flow by making releases less draining and more predictable compared to long-lived branches and unpredictable cycles under the previous model.

1. Chrome Release Cycle
Author: Anthony Laforge (laforge@chromium.org)

2. Our Philosophy
Think of any major website, even the fancy Web 2.HTML5
ones... do they have version numbers?
We took the same approach to our client software as an
online web service.
That is... we treat releases as a means of getting features
out to users and not goals in and of themselves.
It's about flow.

3. How Our Users Work
Users sign up for Chrome release channels based on the
level of stability they want.
Updates happen automatically in the background.
New features and functionality just flow in without any effort
on the user's part.

4. How the Chrome Team Works
Developers work almost exclusively on a single
central trunk (possible due to our try bots and continuous
build infrastructure)
Our branches stem from points on the trunk
We stabilize branches by pulling in changes from trunk (i.e.
everything lands on trunk first)

5. Where we started (v1-4) - On Paper

6. In practice, for that final beta...we'd
Cut a branch (when we thought we had everything)
Merge about ~500 patches (since we didn't have
everything)
Spend weeks stabilizing and re-stabilizing issues.
Ended up working 1-3 months to get a release out the door,
always certainly missing our 13 week plan.
And at the end finally shipping something we were happy
with... but that left us pretty drained (i.e. the bad flow)

7. The chain of events
We'd hold releases, sometimes our branch points, until
features were done, which meant...
Lots of changes got queued up on the trunk, which
caused...
Engineers merging lots of changes to the branch, which led
to...
Instability on the branch that we had to deal with and that
meant...

8. That chain of events...
Long lived branches, which...
Made supporting the branch (i.e. merging changes) more
difficult as we drifted further from the trunk...
All of which led to...
Unpredictable release cycles, with date targets we could
never hit, and....
Engineers who were always in a rush to get their features
into "this" release since we couldn't make any promises
about the schedule

9. Which led me to think...
I need a long vacation.
There has to be a better way.
What's causing things not to flow smoothly?
...Yes...In that order.

10. Primary Goals
Shorten the release cycle and reduce the life span of a
branch (make merges easier)
Make releases more predictable and easier to scope
Reduce the strain on the entire team
Good Bad

11. Goal to Plan - Getting down the cycle
Originally set out a plan to simplify the 12 week cycle, 6
weeks on dev, 6 weeks on beta, and then to stable.
Once diagrammed, using blocks to represent the weeks,
realized that with 3 channels you could have two
overlapping releases running at once, which could get us a
stable release ~ every 6 weeks.

12. Block diagrams

13. It was a start, but it wasn't the full answer
Sure, turning the wheel faster would make some things, like
merges, easier.
But without addressing the scope problems, the flow
wouldn't be any better and would continue
to interrupt releases.
Things wouldn't be any more predictable and the whole
cycle would just fall apart (more puddles, less of a stream).

14. Goal to Plan - Controlling Scope
The pace of the schedule sets the boundaries for the amount
of work that can be completed.
It's important to have specific points in the schedule to
review features and cut scope.
Establish clear expectations (and engineering practice) to
developers that any features not ready to ship at branch will
be disabled (i.e. we only cut post branch, never add).

15. Plan to Pitch
Reached out to the various cross functional groups on the
Chrome team, who would all be impacted, before
approaching our executives.
Engineering, QA, Product, Marketing, Support,
Localization, Security, etc...
There were a lot of concerns to address, but the exercise
forced a lot of thought on the implications of the schedule
change.
It took time, but it made the pitch easier to present to the
leadership and the rest of the team.

16. Concerns
Would large feature development still be possible?
"Yes, engineers would have to work behind flags, however
they can work for as many releases as they need to and can
remove the flag when they are done."
Can the engineers keep up?
"Their pace won't need to change, since features can be
disabled there should be no milestone pressure, things ship
when they are ready."
What would a world look like where we didn't base our
marketing on releases?
"We market features, not releases."

17. And so we implemented it
11 week overlapping schedules.

18. Our General Rules
The branch point is the end of our development cycle
Features only get disabled post branch point
Features should be engineered so that they can be disabled
easily (1 patch)
Only stability, security, and critical regressions can ever
block a release

19. Things we struggled with
Overcoming team inertia (particularly when we cut scope)
Saying no consistently to the team
Fighting the urge to return to date driven management
decisions
We initially didn't solve the trunk->dev->branch time to
patch problem (daily channel helped).
Setting the right burn down point (i.e. branch point).
Disabling features.

20. Key Lessons
Having clear and concise rules is important.
Predictable schedules cut down on communication costs
and team confusion.
It takes work and fore-thought to disable features.
Diligent feature tracking is important.

21. Conclusion
Speed alone isn't always the right answer, it's about keeping
things running smoothly.
For us, scope was getting in the way of that goal.
We basically wanted to operate more like trains leaving Grand Central Station
(regularly scheduled and always on time), and less like taxis leaving the Bronx
(ad hoc and unpredictable).