Code reviews are mandatory for every merge request, you should get familiar with and follow our Code Review Guidelines.
These guidelines also describe who would need to review, approve and merge your, or a community member's, merge request. They also describe the review response time SLO's team members have to abide by.
Every reviewer at GitLab must strive for our reviewer values.
All GitLab engineers can, and are encouraged to, perform a code review on merge requests of colleagues and community contributors. If you want to review merge requests, you can wait until someone assigns you one, but you are also more than welcome to browse the list of open merge requests and leave any feedback or questions you may have.
You can also help community contributors get their merge requests ready, by becoming a Merge Request Coach.
Note that while all engineers can review all merge requests, the ability to accept merge requests is restricted to maintainers.
Maintainers are GitLab engineers who are experts at code review, know the GitLab product and codebase very well, and are empowered to accept merge requests in one or several GitLab Engineering Projects.
Every project should have at least two maintainers, but most should have more. Some projects have separate maintainers for different specialties. For example, the main GitLab codebase has separate maintainers for frontend, backend, and database.
Great engineers are often also great reviewers, but code review is a skill in and of itself and not every engineer, no matter their seniority, will have had the same opportunities to hone that skill. It's also important to note that a big part of being a good maintainer comes from knowing the existing product and codebase extremely well, which lets them spot inconsistencies, edge cases, or non-obvious interactions with other features that would otherwise be missed easily.
Becoming a reviewer/maintainer means you are taking on a broader responsibility beyond your immediate group. Your available capacity should be adjusted accordingly to make room for you to work effectively. There is no strict formula for this as each project comes with a different workload, but do make sure to discuss this with your manager to avoid burnout and to ensure your manager understands how this may impact your team's capacity.
To protect and ensure the quality of the codebase and the product as a whole, people become maintainers only once they have convincingly demonstrated that their reviewing skills are at a comparable level to those of existing maintainers.
For senior+ engineers, being a maintainer is part of their job family unless they have discussed with their manager or Team Member Relations in line with our reasonable accommodation process. Any of the engineering projects considered as part of the product are suitable, provided the individual has been a contributor and an active reviewer of the project. Effective 2022-08-01, we use the following table for the timeframe expectations of maintainership:
|Intermediate Engineers||Maintainership is optional|
|Existing Senior+ Engineer||Existing senior+ engineers who are not already maintainers are encouraged to complete the trainee program in support of our team's productivity and motivation. There is no expected completion timeframe of the trainee program.|
|Newly hired Senior+||During onboarding, newly hired senior+ engineers will be asked to become trainee maintainers instead of reviewers. We expect their maintainership to be complete within 12 months of their onboarding completion.|
|Promotions to Senior||For engineers moving into the Senior role, we expect that they have already become a maintainer prior to promotion.|
Communication happens easier when you are familiar with the person reviewing the code. Take opportunities (for example coffee chats) to get to know reviewers to break the ice and facilitate future communication.
This applies specifically to backend, frontend and database maintainers. Other areas (docs, etc.) may have separate processes documented below.
Before considering maintainership, first you should be a contributor. You should have made at least a few feature or maintenance contributions to the project before you can become a reviewer in the trainee maintainer process. These contributions should be complex enough to give you an understanding of the project's unique domain and design.
Interested reviewers should check in regularly with their manager/mentor to discuss progress towards maintainership and review any recent detailed reviews, for example during their 1-on-1s. Reviewers are encouraged to also seek out a maintainer mentor for further perspective on their reviews. Reviewers are encouraged to think of their eligibility for maintainership in the terms of "I could be ready at any time to be a maintainer as long as it is justified".
After each review is complete, the reviewer should write up a justification about why they believe the merge request is ready to merge. This justification is then reviewed by the maintainer and if the maintainer agrees with the justification they should add a 👍 reaction to the comment, even if they have additional non-blocking comments. The maintainer should leave a comment highlighting any blocking concerns that were missed in the initial review.
At any time, the manager/mentor may choose to open a merge request, adding the reviewer as a maintainer. This merge request should have a justification from the manager/mentor as to why the reviewer should become a maintainer. You are also welcome to open this merge request yourself at any time. There are merge request templates available to help you with the content and steps.
Before opening the merge request, the author should:
Before merging, the manager/mentor should:
If the manager/mentor is given feedback that indicates the reviewer is not ready to become a maintainer: the manager/mentor should close the merge request and provide the feedback directly to the reviewer to address the gaps before the reviewer is re-submitted. The earlier the manager/mentor can solicit this feedback the better.
Handling disagreements in maintainer readiness:
The manager/mentor should seek to understand any concern raised by a current maintainer when they disagree with a trainee maintainer's readiness or qualifications. Use the following guidelines to determine if a single disapproval should veto approvals received in favor of the trainee maintainer.
In order to better inform a decision, the manager should privately reach out to 2 existing maintainers without sharing any personal information regarding the feedback. The manager is ultimately responsible for the readiness of the trainee maintainer and owns the decision to entrust the trainee maintainer with maintainer responsibilities.
After merging, the manager should:
Interested reviewers for the projects below should complete the listed tasks in addition to what is described in How to become a project maintainer to progress from a reviewer to a maintainer.
@gl-databasegroup and respond to @-mentions to the group (reach out to any maintainer on the group to get added). You will get TODOs on gitlab.com for group mentions..
AllFeaturesUseraccess to database lab/postgres.ai if you do not already have
~"database::reviewed"label, reach out to the database group manager to get one. (Example)
gitlab-designproject. If you are interested in becoming a Maintainer of UI (
gitlab-uiprojects, please follow the Engineering Review Workflow.
#pajamas-design-systemSlack channels. If you are not receiving enough MRs to advance in your training, be proactive and work on your own improvements to Pajamas. This will demonstrate overall understanding of the product, as well as quality contributions, and help propel your progress. Maintainers are available to help guide you.
license-dbnamespace. Maintainership is granted per project.
While any reviewer may be recommended by their manager to become a maintainer at any time, reviewers who wish to become maintainers should follow a few basic steps on each review in order to get into a maintainer mindset, and learn from feedback from maintainers.
Create a merge request and indicate your role as a
project-name: trainee_maintainer in your team member entry. Assign MR to your manager for merge.
After each review, reviewers should summarize why they believe a merge request is ready to be merged:
Looks good! I believe this MR resolves the issue and it looks safe because the code change is relatively isolated.
LGTM! I feel this MR is a good iteration. And it has low risk because it is behind a feature flag.
Maintainers should respond to the comment from the reviewer with a 👍 if they agree, and upon merging if there were additional comments they feel should have been caught, they should ping any reviewers so they are aware of the comments.
Some reviewers find it helpful to track their progress. This is not required, but a few ways people have done this are:
If you’ve become a new maintainer, follow these instructions to request relevant permissions that will allow you to fulfill your role:
Training and onboarding new maintainers is an important process. As the engineering team grows and the total number of MRs rapidly expands, the number of MR reviews per maintainer quickly becomes unsustainable.
Recent research has shown that the trainee process for new maintainers is hindered by several key factors:
After consultation with your manager, you may wish or need to transition away from being a reviewer/maintainer. Regardless of the circumstances, it's perfectly OK for this to happen! Responsibilities and workloads change; projects evolve. So it's important to ensure your time is spent on the areas that are most important. To make the change official and to be removed from reviewer roulette:
After a period of transitioning away from being a reviewer/maintainer, you may wish to return to performing these duties. To make the request official, see the section on how to become a project maintainer, creating the tracking issue and Merge Request, referencing previous tracking issue(s) and Merge Request(s) for context. The newly created Merge Request should be assigned to your manager for immediate review as the process can usually be fast tracked.
This is a general purpose template that projects belonging to a specific group and/or projects with less than 10 internal contributors can use to define and document their maintainership process.
Projects may adopt these guidelines for maintainership to help grow maintainers in projects where there are not enough maintainers.
simple_roulettewithin the project to identify MR reviewers.
Smaller projects with a limited number of maintainers can benefit from an accelerated onboarding process. This process is less involved than the main GitLab maintainership, mainly because there is not enough feature work and MRs in these smaller projects. Each project can modify this process to fit their needs.
The onboarding process consists of the following steps:
By following this onboarding process, projects can efficiently add new maintainers with a solid understanding of the codebase and the project's business logic. An example of this process in action can be seen in the GitLab VS Code Extension Project.
Use this lightweight template as a starting point for defining your project's maintainer requirements.
[project or team]Slack channel.
project-name: trainee_maintainerin your team member entry. Assign MR to your manager for merge.
We aim to keep the engineer : maintainer ratio under 6, for both frontend and backend. We track this in the Engineer : Maintainer Ratio dashboard:
We can gauge demand by looking at the Maintainership Demand dashboard, which can be filtered by month, project and technology:
Definitions of metrics:
maintainerspecified in their
Explanation of charts:
Targets are calculated based on the number of available maintainers (described above) and what a "reasonable" number of reviews per maintainer per month is. "Reasonable" has been defined for some areas in separate analysis issues. These are custom targets defined in the "maintainer_custom_targets" Sisense snippet. There are general targets for all other projects based on the number of incoming merge requests to the project. These numbers are a first iteration and were based on the analysis issues, where less demanding projects had fewer maintainers (therefore requiring more monthly reviews per person) and more demanding projects had more maintainers (therefore requiring less monthly reviews per person):
To add a custom target to an area using the
maintainer_custom_targets Sisense snippet:
CASE/WHENstatement based on the project name and optionally technology group
team.ymlfor reviewer roulette. Another reason might be that the project is not using reviewer roulette. In these cases, the project will need to be set up and configured correctly to use reviewer roulette. Finally, the
team.ymlmust match the requirements of the project or area - for example, if reviews in your project are able to go to any maintainer, the
maintainer. If the reviews in your project are separated by specialty, the
maintainer [SPECIALTY]and the merge request should be labeled according to that specialty.
We aim to have enough reviewers and maintainers across timezones to ensure that there are people available to review MRs in a timely manner while keeping review load at a reasonable level. We track this in the Reviewer/Maintainer Availability and Capacity dashboard:
All wider community members, and their organizations, can
contribute. We strongly believe that contributing to
open source, and particularly to GitLab is a competitive advantage for organizations and their members, and want to
reward those organizations for doing so. GitLab highly encourages, celebrates & rewards those that contribute in
frequent and atomic iterations. When an organization or individual without affiliations
reaches 20 merged merge requests or more within the last 3 completed months, we consider that organization or individual
Organizations are matched based on the
Organization field in your profile. GitLab
can also match individuals to organizations using other metadata available to the Contributor Success team. Create an
issue in the Contributor Success queue if you
think you or your organization should qualify but is not receiving the label
Leading Organization on your merge
Leading Organization is entitled to a review response SLO. This entitlement will be
awarded in the beginning of each month. Merge requests that were created during the time in which an organization is
entitled to the
Leading Organization status, will receive the label
Leading Organization = 20 merged Merge Requests or more within the last 3 completed months.
Eligible merge requests include contributions to the GitLab product and documentation. Contributions to the www-gitlab-com repository (e.g. the GitLab handbook) are not currently included or entitled to a review response SLO.
Our Code Review Guidelines states that we default to assigning reviews to team members with domain expertise.
We currently don't provide rigid rules for what qualifies a team member as a domain expert and instead we use a boring solution of implicit and self-identification.
The only requirement to be considered a domain expert is to have substantial experience with a specific technology, product feature or area of the codebase. We leave it up to the team member to decide whether they meet this criteria.
domain_expertiseproperty and list all domain expertise keys.
webpack: display_name: Webpack link: https://webpack.js.org/ frontend_architecture: display_name: Frontend Architecture link: https://docs.gitlab.com/ee/development/fe_guide/architecture.html
domain_expertise: - webpack - frontend_architecture
When self-identifying as a domain expert, it is recommended to assign the MR to be merged by an already established Domain Expert or a corresponding Engineering Manager.
The expertise of a team member can be seen on the Engineering Projects page.
Because unblocking others is always a top priority, reviewers are expected to review merge requests in a timely manner, even when this may negatively impact their other tasks and priorities.
Doing so allows everyone involved in the merge request to iterate faster as the context is fresh in memory, and improves contributors' experience significantly.
To ensure swift feedback to ready-to-review code, we maintain a
Review-response Service-level Objective (SLO).
The SLO applies to GitLab team members and Leading Organizations, but not to other wider community contributors.
The SLO is defined as:
Review-response SLO = (time when review is provided) - (time MR is assigned to reviewer)
The SLO value depends on the author of the merge request:
Review-responseSLO < 2 business days
Review-responseSLO < 4 business days
If you don't think you can review a merge request in the
time frame, let the author know as soon as possible in the comments
(no later than 36 hours after first receiving the review request)
and try to help them find another reviewer or maintainer who is able to, so that they can be unblocked
and get on with their work quickly. Remove yourself as a reviewer.
If you are at capacity and are unable to accept any more reviews until
some have been completed, communicate this through your GitLab status by setting
:red_circle: emoji and mentioning that you are at capacity in the status
text. This guides contributors to pick a different reviewer, helping us to
meet the SLO.
Reviewers may also communicate their status through the use of several other emoji. For more details on these other statuses, please refer to the code review page in the developer documentation.
Of course, if you are out of office and have communicated this through your GitLab.com Status, authors are expected to realize this and find a different reviewer themselves.
When a merge request author has been blocked for longer than
Review-response SLO, they are free to remind the reviewer through Slack or add
When you are assigned to review an MR and you are not able to get to it within the
Review-response SLO, you should leave a comment on the MR informing the author of your delayed response. If possible, you should also indicate when the author can expect your feedback or help them find an alternative reviewer.
As the author of an MR you should reassign to another reviewer or maintainer if the
Review-response SLO has not been met and you have been unable to contact the assignee.
Some GitLab projects use GitLab's CODEOWNERS file feature to manage approvals for specific file paths and types. In the
gitlab-org/gitlab project, we use a combination of CODEOWNERS approval rules plus MR approval settings in order to follow segregation of duties best practices. This section describes the process for updating the eligible approvers for CODEOWNERS changes for the
The Code Owners for the CODEOWNERS file itself are managed with a rule in the file. For example:
CODEOWNERS @gitlab-org/development-leaders @gitlab-org/tw-leadership
There are two ways to update the Code Owner(s) of the