owners

OWNERS files

Overview

OWNERS files are used to designate responsibility over different parts of the Kubernetes codebase. Today, we use them to assign the reviewer and approver roles used in our two-phase code review process. Our OWNERS files were inspired by Chromium OWNERS files, which in turn inspired GitHub’s CODEOWNERS files.

The velocity of a project that uses code review is limited by the number of people capable of reviewing code. The quality of a person’s code review is limited by their familiarity with the code under review. Our goal is to address both of these concerns through the prudent use and maintenance of OWNERS files

OWNERS spec

The k8s.io/test-infra/prow/repowners package is the main consumer of OWNERS files. If this page is out of date, look there.

OWNERS

Each directory that contains a unit of independent code or content may also contain an OWNERS file. This file applies to everything within the directory, including the OWNERS file itself, sibling files, and child directories.

OWNERS files are in YAML format and support the following keys:

  • approvers: a list of GitHub usernames or aliases that can /approve a PR
  • labels: a list of GitHub labels to automatically apply to a PR
  • options: a map of options for how to interpret this OWNERS file, currently only one:
    • no_parent_owners: defaults to false if not present; if true, exclude parent OWNERS files. Allows the use case where a/deep/nested/OWNERS file prevents a/OWNERS file from having any effect on a/deep/nested/bit/of/code
  • reviewers: a list of GitHub usernames or aliases that are good candidates to /lgtm a PR

All users are expected to be assignable. In GitHub terms, this means they are either collaborators of the repo, or members of the organization to which the repo belongs.

A typical OWNERS file looks like:

approvers:
  - alice
  - bob     # this is a comment
reviewers:
  - alice
  - carol   # this is another comment
  - sig-foo # this is an alias

OWNERS_ALIASES

Each repo may contain at its root an OWNERS_ALIAS file.

OWNERS_ALIAS files are in YAML format and support the following keys:

  • aliases: a mapping of alias name to a list of GitHub usernames

We use aliases for groups instead of GitHub Teams, because changes to GitHub Teams are not publicly auditable.

A sample OWNERS_ALISES file looks like:

aliases:
  sig-foo:
    - david
    - erin
  sig-bar:
    - bob
    - frank

GitHub usernames and aliases listed in OWNERS files are case-insensitive.

Code Review using OWNERS files

This is a simplified description of our full PR testing and merge workflow that conveniently forgets about the existence of tests, to focus solely on the roles driven by OWNERS files. Please see below for details on how specific aspects of this process may be configured on a per-repo basis.

The Code Review Process

  • The author submits a PR
  • Phase 0: Automation suggests reviewers and approvers for the PR
    • Determine the set of OWNERS files nearest to the code being changed
    • Choose at least two suggested reviewers, trying to find a unique reviewer for every leaf OWNERS file, and request their reviews on the PR
    • Choose suggested approvers, one from each OWNERS file, and list them in a comment on the PR
  • Phase 1: Humans review the PR
    • Reviewers look for general code quality, correctness, sane software engineering, style, etc.
    • Anyone in the organization can act as a reviewer with the exception of the individual who opened the PR
    • If the code changes look good to them, a reviewer types /lgtm in a PR comment or review; if they change their mind, they /lgtm cancel
    • Once a reviewer has /lgtm‘ed, prow (@k8s-ci-robot) applies an lgtm label to the PR
  • Phase 2: Humans approve the PR
    • The PR author /assign’s all suggested approvers to the PR, and optionally notifies them (eg: “pinging @foo for approval”)
    • Only people listed in the relevant OWNERS files, either directly or through an alias, can act as approvers, including the individual who opened the PR
    • Approvers look for holistic acceptance criteria, including dependencies with other features, forwards/backwards compatibility, API and flag definitions, etc
    • If the code changes look good to them, an approver types /approve in a PR comment or review; if they change their mind, they /approve cancel
    • prow (@k8s-ci-robot) updates its comment in the PR to indicate which approvers still need to approve
    • Once all approvers (one from each of the previously identified OWNERS files) have approved, prow (@k8s-ci-robot) applies an approved label
  • Phase 3: Automation merges the PR:
    • If all of the following are true:
    • All required labels are present (eg: lgtm, approved)
    • Any blocking labels are missing (eg: there is no do-not-merge/hold, needs-rebase)
    • And if any of the following are true:
    • there are no presubmit prow jobs configured for this repo
    • there are presubmit prow jobs configured for this repo, and they all pass after automatically being re-run one last time
    • Then the PR will automatically be merged

Quirks of the Process

There are a number of behaviors we’ve observed that while possible are discouraged, as they go against the intent of this review process. Some of these could be prevented in the future, but this is the state of today.

  • An approver’s /lgtm is simultaneously interpreted as an /approve
    • While a convenient shortcut for some, it can be surprising that the same command is interpreted in one of two ways depending on who the commenter is
    • Instead, explicitly write out /lgtm and /approve to help observers, or save the /lgtm for a reviewer
    • This goes against the idea of having at least two sets of eyes on a PR, and may be a sign that there are too few reviewers (who aren’t also approver)
  • An approver can /approve no-issue to bypass the requirement that PR’s must have linked issues
    • There is disagreement within the community over whether requiring every PR to have a linked issue provides value
    • Protest is being expressed in the form of overuse of /approve no-issue
    • Instead, suggest to the PR author that they edit the PR description to include a linked issue
    • This is a sign that we need to actually deliver value with linked issues, or be able to define what a “trivial” PR is in a machine-enforceable way to be able to automatically waive the linked issue requirement
  • Technically, anyone who is a member of the kubernetes GitHub organization can drive-by /lgtm a PR
    • Drive-by reviews from non-members are encouraged as a way of demonstrating experience and intent to become a collaborator or reviewer
    • Drive-by /lgtm’s from members may be a sign that our OWNERS files are too small, or that the existing reviewers are too unresponsive
    • This goes against the idea of specifying reviewers in the first place, to ensure that author is getting actionable feedback from people knowledgeable with the code
  • Reviewers, and approvers are unresponsive
    • This causes a lot of frustration for authors who often have little visibility into why their PR is being ignored
    • Many reviewers and approvers are so overloaded by GitHub notifications that @mention’ing is unlikely to get a quick response
    • If an author /assign’s a PR, reviewers and approvers will be made aware of it on their PR dashboard
    • An author can work around this by manually reading the relevant OWNERS files, /unassign‘ing unresponsive individuals, and /assign‘ing others
    • This is a sign that our OWNERS files are stale; pruning the reviewers and approvers lists would help with this
  • Authors are unresponsive
    • This costs a tremendous amount of attention as context for an individual PR is lost over time
    • This hurts the project in general as its general noise level increases over time
    • Instead, close PR’s that are untouched after too long (we currently have a bot do this after 90 days)

Automation using OWNERS files

~mungegithub~ is deprecated

Mungegithub’s blunderbuss and submit-queue mungers are currently used for kubernetes/kubernetes. Their equivalents are the prow blunderbuss plugin, and prow’s tide cmd. These docs will be removed once kubernetes/kubernetes has transitioned over to tide.

~Mungegithub polls GitHub, and “munges” things it finds, including issues and pull requests. It is stateful, in that restarting it means it loses track of which things it has munged at what time.~

  • ~munger: blunderbuss~
    • ~responsible for determining reviewers and assigning to them~
  • munger: submit-queue
    • responsible for merging PR’s
    • responsible for updating a GitHub status check explaining why a PR can’t be merged (eg: a missing lgtm or approved label)

prow

Prow receives events from GitHub, and reacts to them. It is effectively stateless. The following pieces of prow are used to implement the code review process above.

  • cmd: tide
    • per-repo configuration:
    • labels: list of labels required to be present for merge (eg: lgtm)
    • missingLabels: list of labels required to be missing for merge (eg: do-not-merge/hold)
    • reviewApprovedRequired: defaults to false; when true, require that there must be at least one approved pull request review present for merge
    • merge_method: defaults to merge; when squash or rebase, use that merge method instead when clicking a PR’s merge button
    • merges PR’s once they meet the appropriate criteria as configured above
    • if there are any presubmit prow jobs for the repo the PR is against, they will be re-run one final time just prior to merge
  • plugin: assign
    • assigns GitHub users in response to /assign comments on a PR
    • unassigns GitHub users in response to /unassign comments on a PR
  • plugin: approve
    • per-repo configuration:
    • issue_required: defaults to false; when true, require that the PR description link to an issue, or that at least one approver issues a /approve no-isse
    • implicit_self_approve: defaults to false; when true, if the PR author is in relevant OWNERS files, act as if they have implicitly /approve’d
    • adds the approved label once an approver for each of the required OWNERS files has /approve’d
    • comments as required OWNERS files are satisfied
    • removes outdated approval status comments
  • plugin: blunderbuss
    • determines reviewers and requests their reviews on PR’s
  • plugin: lgtm
    • adds the lgtm label when a reviewer comments /lgtm on a PR
    • the PR author may not /lgtm their own PR
  • pkg: k8s.io/test-infra/prow/repowners
    • parses OWNERS and OWNERS_ALIAS files
    • if the no_parent_owners option is encountered, parent owners are excluded from having any influence over files adjacent to or underneath of the current OWNERS file

Maintaining OWNERS files

OWNERS files should be regularly maintained.

We encourage people to self-nominate or self-remove from OWNERS files via PR’s. Ideally in the future we could use metrics-driven automation to assist in this process.

We should strive to:

  • grow the number of OWNERS files
  • add new people to OWNERS files
  • ensure OWNERS files only contain org members and repo collaborators
  • ensure OWNERS files only contain people are actively contributing to or reviewing the code they own
  • remove inactive people from OWNERS files

Bad examples of OWNERS usage:

  • directories that lack OWNERS files, resulting in too many hitting root OWNERS
  • OWNERS files that have a single person as both approver and reviewer
  • OWNERS files that haven’t been touched in over 6 months
  • OWNERS files that have non-collaborators present

Good examples of OWNERS usage:

  • team aliases are used that correspond to sigs
  • there are more reviewers than approvers
  • the approvers are not in the reviewers section
  • OWNERS files that are regularly updated (at least once per release)