Code Review Process

In order to manage incoming pull requests effectively, and provide timely feedback and/or acceptance this document serves as a guideline for the review process and outlines the expectations for those submitting code to the project as well as those reviewing the code. Code is reviewed for acceptance by at least one core team member (later referred to as committers), but comments and suggestions from others are encouraged and welcome.

The process is intended to provide timely and actionable feedback for any submission.

Asking For Help

cloud-init contributors, potential contributors, community members and users are encouraged to ask for any help that they need. If you have questions about the code review process, or at any point during the code review process, these are the available avenues:

  • if you have an open Pull Request, comment on that pull request
  • join the #cloud-init channel on the Libera IRC network and ask away
  • send an email to the cloud-init mailing list, cloud-init@lists.launchpad.net

These are listed in rough order of preference, but use whichever of them you are most comfortable with.

Goals

This process has the following goals:

  • Ensure code reviews occur in a timely fashion and provide actionable feedback if changes are desired.
  • Ensure the minimization of ancillary problems to increase the efficiency for those reviewing the submitted code

Role Definitions

Any code review process will have (at least) two involved parties. For our purposes, these parties are referred to as Proposer and Reviewer. (We also have the Committer role which is a special case of the Reviewer role.) The terms are defined here (and the use of the singular form is not meant to imply that they refer to a single person):

Proposer
The person proposing a pull request (hereafter known as a PR).
Reviewer
A person who is reviewing a PR.
Committer
A cloud-init core developer (i.e. a person who has permission to merge PRs into master).

Prerequisites For Landing Pull Requests

Before a PR can be landed into master, the following conditions must be met:

  • the CLA has been signed by the Proposer (or is covered by an entity-level CLA signature)
  • all required status checks are passing
  • at least one “Approve” review from a Committer
  • no “Request changes” reviews from any Committer

The following conditions should be met:

  • any Python functions/methods/classes have docstrings added/updated
  • any changes to config module behaviour are captured in the documentation of the config module
  • any Python code added has corresponding unit tests
  • no “Request changes” reviews from any Reviewer

These conditions can be relaxed at the discretion of the Committers on a case-by-case basis. Generally, for accountability, this should not be the decision of a single Committer, and the decision should be documented in comments on the PR.

(To take a specific example, the cc_phone_home module had no tests at the time PR #237 was submitted, so the Proposer was not expected to write a full set of tests for their minor modification, but they were expected to update the config module docs.)

Non-Committer Reviews

Reviews from non-Committers are always welcome. Please feel empowered to review PRs and leave your thoughts and comments on any submitted PRs, regardless of the Proposer.

Much of the below process is written in terms of the Committers. This is not intended to reflect that reviews should only come from that group, but acknowledges that we are ultimately responsible for maintaining the standards of the codebase. It would be entirely reasonable (and very welcome) for a Reviewer to only examine part of a PR, but it would not be appropriate for a Committer to merge a PR without full scrutiny.

Opening Phase

In this phase, the Proposer is responsible for opening a pull request and meeting the prerequisites laid out above.

If they need help understanding the prerequisites, or help meeting the prerequisites, then they can (and should!) ask for help. See the Asking For Help section above for the ways to do that.

These are the steps that comprise the opening phase:

  1. The Proposer opens PR

  2. CI runs automatically, and if

    CI fails

    The Proposer is expected to fix CI failures. If the Proposer doesn’t understand the nature of the failures they are seeing, they should comment in the PR to request assistance, or use another way of Asking For Help.

    (Note that if assistance is not requested, the Committers will assume that the Proposer is working on addressing the failures themselves. If you require assistance, please do ask for help!)

    CI passes

    Move on to the Review Phase.

Review Phase

In this phase, the Proposer and the Reviewers will iterate together to, hopefully, get the PR merged into the cloud-init codebase. There are three potential outcomes: merged, rejected permanently, and temporarily closed. (The first two are covered in this section; see Inactive Pull Requests for details about temporary closure.)

(In the below, when the verbs “merge” or “squash merge” are used, they should be understood to mean “squash merged using the GitHub UI”, which is the only way that changes can land in cloud-init’s master branch.)

These are the steps that comprise the review phase:

  1. The Committers assign a Committer to the PR

    This Committer is expected to shepherd the PR to completion (and merge it, if that is the outcome reached). This means that they will perform an initial review, and monitor the PR to ensure that the Proposer is receiving any assistance that they require. The Committers will perform this assignment on a daily basis.

    This assignment is intended to ensure that the Proposer has a clear point of contact with a cloud-init core developer, and that they get timely feedback after submitting a PR. It is not intended to preclude reviews from any other Reviewers, nor to imply that the Committer has ownership over the review process.

    The assigned Committer may choose to delegate the code review of a PR to another Reviewer if they think that they would be better suited.

    (Note that, in GitHub terms, this is setting an Assignee, not requesting a review.)

  2. That Committer performs an initial review of the PR, resulting in one of the following:

    Approve

    If the submitted PR meets all of the Prerequisites For Landing Pull Requests and passes code review, then the Committer will squash merge immediately.

    There may be circumstances where a PR should not be merged immediately. The wip label will be applied to PRs for which this is true. Only Committers are able to apply labels to PRs, so anyone who believes that this label should be applied to a PR should request its application in a comment on the PR.

    The review process is DONE.

    Approve (with nits)

    If the Proposer submits their PR with “Allow edits from maintainer” enabled, and the only changes the Committer requests are minor “nits”, the Committer can push fixes for those nits and immediately squash merge. If the Committer does not wish to fix these nits but believes they should block a straight-up Approve, then their review should be “Needs Changes” instead.

    A nit is understood to be something like a minor style issue or a spelling error, generally confined to a single line of code.

    If a Committer is unsure as to whether their requested change is a nit, they should not treat it as a nit.

    (If a Proposer wants to opt-out of this, then they should uncheck “Allow edits from maintainer” when submitting their PR.)

    The review process is DONE.

    Outright rejection

    The Committer will close the PR, with useful messaging for the Proposer as to why this has happened.

    This is reserved for cases where the proposed change is completely unfit for landing, and there is no reasonable path forward. This should only be used sparingly, as there are very few cases where proposals are completely unfit.

    If a different approach to the same problem is planned, it should be submitted as a separate PR. The Committer should include this information in their message when the PR is closed.

    The review process is DONE.

    Needs Changes

    The Committer will give the Proposer a clear idea of what is required for an Approve vote or, for more complex PRs, what the next steps towards an Approve vote are.

    The Proposer will ask questions if they don’t understand, or disagree with, the Committer’s review comments.

    Once consensus has been reached, the Proposer will address the review comments.

    Once the review comments are addressed (as well as, potentially, in the interim), CI will run. If CI fails, the Proposer is expected to fix CI failures. If CI passes, the Proposer should indicate that the PR is ready for re-review (by @ing the assigned reviewer), effectively moving back to the start of this section.

Inactive Pull Requests

PRs will be temporarily closed if they have been waiting on Proposer action for a certain amount of time without activity. A PR will be marked as stale (with an explanatory comment) after 14 days of inactivity. It will be closed after a further 7 days of inactivity.

These closes are not considered permanent, and the closing message should reflect this for the Proposer. However, if a PR is reopened, it should effectively enter the Opening Phase again, as it may need some work done to get CI passing again.