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Contributing to Kubeflow

How to start contributing to Kubeflow

Welcome to the Kubeflow project!

Getting started as a Kubeflow contributor

This document is the single source of truth for how to contribute to the code base. We’d love to accept your patches and contributions to this project. There are just a few small guidelines you need to follow.

Sign the CLA

Contributions to this project must be accompanied by a Contributor License Agreement. You (or your employer) retain the copyright to your contribution, this simply gives us permission to use and redistribute your contributions as part of the project. Head over to to see your current agreements on file or to sign a new one.

You generally only need to submit a CLA once, so if you’ve already submitted one (even if it was for a different project), you probably don’t need to do it again.

Follow the code of conduct

Please make sure to read and observe our Code of Conduct.

Consider participating in Kubeflow user research

Maggie Lynn, a user experience researcher, is conducting user studies to inform future developments for Kubeflow. These typically involve a one hour study session conducted online with a thank you gift for providing your feedback. As a member of the Kubeflow community, your feedback and expertise are extremely valuable to us, so if you have time in the next month, please consider participating. To gather your interest, availability, and some basic information about you, please fill out this form where you’ll find out more details about this research opportunity:

Joining the community

Follow these instructions if you want to

  • Become a member of the Kubeflow GitHub org (see below)
  • Become part of the Kubeflow build cop or release teams
  • Be recognized as an individual or organization contributing to Kubeflow

Joining the Kubeflow GitHub Org

Before asking to join the community, we ask that you first make a small number of contributions to demonstrate your intent to continue contributing to Kubeflow.

There are are a number of ways to contribute to Kubeflow

  • Submit PRs
  • File issues reporting bugs or providing feedback
  • Answer questions on Slack or GitHub issues

You can use this table to see how many contributions you’ve made

  • Note: This only counts GitHub related ways of contributing

When you are ready to join

  • Send a PR adding yourself as a member in org.yaml
  • After the PR is merged an admin will send you an invite
    • This is a manual process that’s generally run a couple times a week
    • If a week passes without receiving an invite reach out on kubeflow#community


If you would like your company or organization to be acknowledged for contributing to Kubeflow or participating in the community (being a user counts) please send a PR adding the relevant info to member_organizations.yaml.

If you want your employee’s GitHub contributions to be attributed to your company please ask them to set the company field in their GitHub profile.

Community discussions

There are many ways to contribute! Join one of our communication channels, attend a community meeting, get to know the community. Read the details in our community guide.

Your first contribution

Find something to work on

Help is always welcome! For example, documentation (like the text you are reading now) can always use improvement. There’s always code that can be clarified and variables or functions that can be renamed or commented. There’s always a need for more test coverage. You get the idea - if you ever see something you think should be fixed, you should own it. Here is how you get started.

Starter issues

To find Kubeflow issues that make good entry points, look at the following tags:

Owners files and PR workflow

Our PR workflow is nearly identical to Kubernetes’. Most of these instructions are a modified version of Kubernetes’ contributors and owners guides.

Overview of OWNERS files

OWNERS files are used to designate responsibility over different parts of the Kubeflow 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


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:

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


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_ALIASES file looks like:

    - david
    - erin
    - bob
    - frank

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

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)
  • Technically, anyone who is a member of the Kubeflow 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


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:
    • 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:

  • 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)

Last modified 28.04.2019: Resolved typos (#665) (44f20b5)