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Version: 0.1

Warning: This document is incomplete. We’ve added it to the repo before it’s finished because we would like a couple of trial runs before we say we’re happy, and we would like something to refer to during those reviews.

Architecture Review Process


Architectural Reviews within the Firefox organization fall into two categories: “Roadmap” and “Design”.

The function of a Roadmap Review is to decide if a thing should be done. The goal is to bring together a packet of data to inform a management decision to provide resources to make the thing happen. A Roadmap Review should happen early in the process so that build time isn’t wasted on a “No” decision, but so that enough information is available to management.

A Design Review is to decide if the thing should be done in a particular way. The goal is to ensure that the problem space is understood well enough that a realistic bug breakdown can be made, that those working on the problem all agree on the challenge, and that work can be prioritized to hit the hardest parts of the problem first (in order to get early warning if the hard parts prove impossible or to inform schedule projections early).


For both a Roadmap Review and a Design Review the timetable is as follows:

  1. The team should set the stage:
    • Summarize in one or two sentences the proposal to be reviewed. This should be agreed between the team asking for review and the reviewer.
    • Find a reviewer:
      • For a Roadmap Review this will be the least senior manager with the ability to address the problem in its entirety.
      • For a Design Review this will be an experienced engineer in the problem domain outside of the team willing to put time into the problem. As engineers don’t review their own code they shouldn’t review their own designs. The principle is to get the most informed and least biased feedback possible.
    • Optionally, for larger reviews, find someone to chair the review. This can facilitate the process (i.e. scheduling the meeting, managing the clock, ensuring minutes are taken, etc.) and enables the reviewer to concentrate on the review itself. The rest of this document uses ‘chair’ for the administrative role. For smaller reviews the reviewer also does the tasks of the chair.
  2. The team produces a Review Packet designed to document the proposal identified in step 1. The production of the Review Packet is expected to be collaborative and iterative to ensure that the review focuses on the key issues so the team presents its best case. This is particularly true of a Roadmap Review where the consequences of the review are likely to be more significant. The Review Packet includes:
    • A lay summary of the problem space which is focused on defining a shared language and identifying the key forces behind the problem
    • A list of the groups directly affected by the proposal to ensure that the review meeting includes representatives from those groups.
    • A vision of what the project will achieve on completion
    • A brief that explains what the team is proposing. This should read more like an encyclopedia entry than a marketing document. The audience is the people in the review; i.e. this should attempt to plug organizational documentation holes. The documentation process should not be more onerous than is required for the review. The brief should identify:
      • the architecture being proposed
      • the non-functional requirements, like accessibility, performance, security, and stability
      • relevant business goals, such as improving user satisfaction and retention
      • scenarios that exercise the requirements/goals against the proposed architecture
      • how the proposal handles these scenarios
      • what review and discussion of the proposed architecture has already happened (and with whom)
    • A competitive analysis suggesting alternatives, costs, and opportunities
  3. The reviewer creates a list of questions to be discussed during the review. These questions should be:
    • Open-ended
    • Made available to the the team prior to the review so they can prepare answers
  4. The chair convenes a review meeting. The discussions of this meeting should be carefully minuted.
    • The meeting should have a limited attendance to avoid a sprawling unfocussed meeting, but it should include:
      • The team making the proposal
      • Others who will provide valuable input, taking care to:
        • Select a full range of perspectives
        • Avoid “stacking the deck” with too many people that think the same way
    • A suggested agenda for the review meeting:
      • Short opening statement by the team on the current state of play
      • Discussion of Questions and Answers (see 3. above)
      • A step back to discuss if the proposal is right in the wider context

The review meeting should be a discussion of the issues, but should avoid feeling pressured to make a decision. The goal is to understand the issues raised by the question(s) and the background from the review packet, and to add to it wisdom from the people at the review. The meeting may decide to alter the questions and undergo a subsequent review. We should be very open about conversations that happen after the review meeting.

The ideal review process scales well. The same basic system should work for a quick 2 person decision over the best way to design a certain feature, and for a critical organization-wide decision about a path to take. The term “team” is used above although we strongly recommend design reviews for smaller questions. If you feel yourself wondering if some design is best, it should be easy to perform a review.

For particularly small reviews it is possible to merge a roadmap review and design review into a single review, in which case the question is both ‘should we do this’, and ‘should we do it this way’. It is possible to conduct combined reviews where the total time for the review for all participants is 1 working day.

For both a Roadmap Review and a Design Review the goal is to hear perspectives that will lead to a better definition of a problem or solution, and better judgment about whether it should be solved or how to solve it.


Key considerations

Outputs and Audience

The first two considerations define the goals of the review process and are two sides of the same coin.

The audience of a Roadmap Review is those “up the chain” of decision makers and the audience of a Design Review is those running “down the chain” of implementors.

A Roadmap Review should focus on:

The key outcome is firstly, senior management investing in the problem space and building consensus around a shared reality. Secondly, to provide documentation of both the goals and assumptions of the project to aid later evaluation.

A Design Review should focus on:

The key outcome for middle management is to understand the value proposition and the path to success. The key outcome for engineers is firstly to understand the design constraints and the tradeoffs between them, which is important to avoid unnecessary re-work when implementation reality causes a re-think. Secondly, to provide a proposal detailed enough to begin an initial breakdown of engineering work for the proposal (although the work implied by the proposal should not be filed prior to the completion of the review).

Structure and Inputs

The second two considerations shape how the review process actually happens.

The reviewer and the team frame the proposal at the start of the process to ensure agreement on what should be tested. The reviewer is accountable for summarizing the response to the proposal following the review process.

In order to agree on the proposal, the reviewer and the team/technical lead or principals will generally have an initial meeting. This meeting should be as small as possible and is intended to:

Subsequently, the team prepares a review packet detailing the problem space and their approach.

The goal is to have the reviewer and the team establish some shared reality informally, and then to have the team document this and explain how their proposal would address the problem.

The reviewer then evaluates and refines the team’s document with the assistance of domain experts and the identified stakeholders. Hopefully the consulted stakeholders concur with the framing of the problem and are aligned behind the architectural approach, but perhaps they are not. The reviewer collects such concerns and presents them. This should be a collaborative process whereby the architectural review functions to document a problem and a proposed solution, in which case the reviewer can solicit response from the team.

Process and Conduct

Involving the team and the reviewer informally and subsequently sharing ownership of a document is designed to seed a collaborative process. A particular benefit is avoiding drift between the proposal and the focus of the review.

An Architecture Review process can be formally mandated. This may work in environments with a large degree of formality and process. This isn’t how Mozilla works. For an Architecture Review process to be successful at Mozilla it must be beneficial to the team undergoing review.

The primary informal output of a review should be learning. It is expected that go/no-go decisions will be the result of additional learning rather than the team seeing a ‘no-go’ as something that needs fighting. Imposed decisions may be required, but learning is a preferred outcome.

Maturity and Dissemination

The final two considerations shape what is reviewed and how the review concludes.

A project under review will be in one of the following states:

Generally our review process focuses on projects in the “Roadmap” or “Design” stages. However a project in the “Execution” or “Landing” stage may need subsequent review to decide if the project is being done the correct way, or if it should be continued at all, so it may return to either of the “Roadmap” or “Design” phases.

After the review, the reviewer and responsible decision makers should provide concrete recommendations and examples for the next teams to undergo the review process. The results should be disseminated as widely as possible, with the package documents and recommendation document archived. Some version of the decision should be publicly linked, so that it can be the decision of record, to which blog posts, mailing list posts, the message saying that the GitHub repository is obsolete, etc., can refer. The goal is to avoid critical technical and resourcing decisions being internally settled and only — later, begrudgingly — being made public on some mailing list.


A number of reviews have been completed and can be used as a template for a successful architectural review. XBL Removal was the first example of a design review, Sync and Storage was the first roadmap review, however any of the documents on this website with a title that includes “review” could be used.

Additional Reading

Multiple Perspectives On Technical Problems and Solutions - John Allspaw - 2017

Describes how Etsy’s architecture review process evolved. A solid write-up of the social side of an Architecture Review process in an environment that is likely closer to Mozilla’s than many of the other write-ups.

Fundamental: engineering decision-making is a socially constructed activity

We called these “something new” things departures. … the basic idea is that there are costs … for making departures that attempt to solve a local problem without thinking about the global effects it can have on an organization.

Architecture Reviews - Grady Booch - 2010

A formal write-up from someone who spends a significant time in Architecture Reviews. I’ve not found the paper online, but the MP3 is an audio version of the paper (with bonus guitar-riff intro). This IBM process suffers from lack of attention to the social aspects, but is helpful in digging into the mechanics of the review itself.

A Toolbox of Software Architecture Review Techniques - Jason Baragry - 2014, 2015

Jason Baragry reviews approaches to architecture review and notes some potential pitfalls.

Architecturally significant requirements are often hard to identify, the architecturally significant decisions are often not documented, and the way the decisions interrelate is often not easily understood. A significant part of the review process is often teasing these out.

Software Architecture Review and Assessment (SARA) Report - Kruchten et al. - 2002

Formal process with input from a number of companies which targets a more enterprise environment than exists at Mozilla, however the process is clearly defined.

A software architecture is a set of concepts and design decisions about structure and texture of software that must be made prior to concurrent engineering (i.e., implementation) to enable effective satisfaction of architecturally significant, explicit functional and quality requirements, along with implicit requirements of the problem and the solution domains.

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