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Kubernetes Enhancement Proposal Process

Table of Contents

Summary

A standardized development process for Kubernetes is proposed, in order to:

  • provide a common structure for proposing changes to Kubernetes
  • ensure that the motivation for a change is clear
  • allow for the enumeration of stability milestones and stability graduation criteria
  • persist project information in a Version Control System (VCS) for future Kubernauts
  • support the creation of high-value, user-facing information such as:
    • an overall project development roadmap
    • motivation for impactful user-facing changes
  • reserve GitHub issues for tracking work in flight, instead of creating "umbrella" issues
  • ensure community participants can successfully drive changes to completion across one or more releases while stakeholders are adequately represented throughout the process

This process is supported by a unit of work called a Kubernetes Enhancement Proposal, or KEP. A KEP attempts to combine aspects of

  • a feature, and effort-tracking document
  • a product requirements document
  • a design document

into one file, which is created incrementally in collaboration with one or more Special Interest Groups (SIGs).

Motivation

For cross-project SIGs such as SIG Release, an abstraction beyond a single GitHub Issue or pull request seems to be required in order to understand and communicate upcoming changes to Kubernetes. In a blog post describing the road to Go 2, Russ Cox explains:

that it is difficult but essential to describe the significance of a problem in a way that someone working in a different environment can understand

It is vital for the project to be able to track the chain of custody for a proposed enhancement from conception through implementation.

Without a standardized mechanism for describing important enhancements, our talented technical writers and product managers struggle to weave a coherent narrative explaining why a particular release is important. Additionally, adopters of critical infrastructure such as Kubernetes need a forward-looking roadmap in order to plan their adoption strategies.

The purpose of the KEP process is to reduce the amount of "tribal knowledge" in our community. By moving decisions from a smattering of mailing lists, video calls and hallway conversations into a well tracked artifact, this process aims to enhance communication and discoverability.

A KEP is broken into sections which can be merged into source control incrementally in order to support an iterative development process. An important goal of the KEP process is ensuring that the process for submitting the content contained in design proposals is both clear and efficient. The KEP process is intended to create high-quality, uniform design and implementation documents for SIGs to deliberate.

Stewardship

The following DACI model identifies the responsible parties for KEPs.

Workstream Driver Approver Contributor Informed
KEP Process Stewardship SIG Leadership Community
Enhancement Delivery Enhancement Owner SIG leadership (SIG Chairs + TLs) Enhancement Implementer(s) (may overlap with Driver) Community

Reference-Level Explanation

What Type of Work Should Be Tracked by a KEP

The definition of what constitutes an "enhancement" is a foundational concern for the Kubernetes project. Roughly any Kubernetes user or operator facing enhancement should follow the KEP process. If an enhancement would be described in either written or verbal communication to anyone besides the KEP author or developer, then consider creating a KEP.

Similarly, any technical effort (refactoring, major architectural change) that will impact a large section of the development community should also be communicated widely. The KEP process is suited for this even if it will have zero impact on the typical user or operator.

As the local bodies of governance, SIGs should have broad latitude in describing what constitutes an enhancement that should be tracked through the KEP process. SIGs may find it more helpful to enumerate what does not require a KEP, than what does. SIGs also have the freedom to customize the KEP template according to their SIG-specific concerns. For example, the KEP template used to track API changes will likely have different subsections than the template for proposing governance changes. However, as changes start impacting other SIGs or the larger developer community outside of a SIG, the KEP process should be used to coordinate and communicate.

Enhancements that have major impacts on multiple SIGs should use the KEP process. A single SIG will own the KEP, but it is expected that the set of approvers will span the impacted SIGs. The KEP process is the way that SIGs can negotiate and communicate changes that cross boundaries.

KEPs will also be used to drive large changes that will cut across all parts of the project. These KEPs will be owned by SIG-architecture and should be seen as a way to communicate the most fundamental aspects of what Kubernetes is.

KEP Template

The template for a KEP is precisely defined here.

KEP Metadata

There is a place in each KEP for a YAML document that has standard metadata. This will be used to support tooling around filtering and display. It is also critical to clearly communicate the status of a KEP.

While this defines the metadata schema for now, these things tend to evolve. The KEP template is the authoritative definition of things like the metadata schema.

Metadata items:

  • title Required
    • The title of the KEP in plain language. The title will also be used in the KEP filename. See the template for instructions and details.
  • status Required
    • The current state of the KEP.
    • Must be one of provisional, implementable, implemented, deferred, rejected, withdrawn, or replaced.
  • authors Required
    • A list of authors of the KEP. This is simply the GitHub ID. In the future we may enhance this to include other types of identification.
  • owning-sig Required
    • The SIG most closely associated with this KEP. If code or other artifacts will result from this KEP, then it is expected that this SIG will take responsibility for the bulk of those artifacts.
    • Sigs are listed as sig-abc-def, where the name matches the directory entry in the kubernetes/community repo.
  • participating-sigs Optional
    • A list of SIGs that are involved or impacted by this KEP.
    • A special value of kubernetes-wide will indicate that this KEP has impact across the entire project.
  • reviewers Required
    • Reviewer(s) chosen after triage, according to the proposal process.
    • If not yet chosen, replace with TBD.
    • Same name/contact scheme as authors.
    • Reviewers should be a distinct set from authors.
  • approvers Required
    • Approver(s) chosen after triage, according to the proposal process.
    • Approver(s) are drawn from the impacted SIGs. It is up to the individual SIGs to determine how they pick approvers for KEPs impacting them. The approvers are speaking for the SIG in the process of approving this KEP. The SIGs in question can modify this list as necessary.
    • The approvers are the individuals who decide when to move this KEP to the implementable state.
    • Approvers should be a distinct set from authors.
    • If not yet chosen, replace with TBD.
    • Same name/contact scheme as authors.
  • editor Required
    • Someone to keep things moving forward.
    • If not yet chosen, replace with TBD.
    • Same name/contact scheme as authors.
  • creation-date Required
    • The date that the KEP was first submitted in a PR.
    • In the form yyyy-mm-dd.
    • While this info will also be in source control, it is helpful to have the set of KEP files stand on their own.
  • last-updated Optional
    • The date that the KEP was last changed significantly.
    • In the form yyyy-mm-dd.
  • see-also Optional
    • A list of other KEPs that are relevant to this KEP.
    • In the form KEP-123.
  • replaces Optional
    • A list of KEPs that this KEP replaces. Those KEPs should list this KEP in their superseded-by.
    • In the form KEP-123.
  • superseded-by
    • A list of KEPs that supersede this KEP. Use of this should be paired with this KEP moving into the Replaced status.
    • In the form KEP-123.

KEP Workflow

A KEP has the following states:

  • provisional: The KEP has been proposed and is actively being defined. This is the starting state while the KEP is being fleshed out and actively defined and discussed. The owning SIG has accepted that this work must be done.
  • implementable: The approvers have approved this KEP for implementation.
  • implemented: The KEP has been implemented and is no longer actively changed.
  • deferred: The KEP is proposed but not actively being worked on.
  • rejected: The approvers and authors have decided that this KEP is not moving forward. The KEP is kept around as a historical document.
  • withdrawn: The authors have withdrawn the KEP.
  • replaced: The KEP has been replaced by a new KEP. The superseded-by metadata value should point to the new KEP.

Git and GitHub Implementation

KEPs are checked into the Enhancements repo under the /keps directory. KEPs in SIG specific subdirectories have limited impact outside of the SIG and can leverage SIG-specific OWNERS files.

New KEPs can be checked in with a file name in the form of draft-YYYYMMDD-my-title.md. As significant work is done on the KEP, the authors can assign a KEP number. No other changes should be put in that PR so that it can be approved quickly and minimize merge conflicts. The KEP number can also be done as part of the initial submission if the PR is likely to be uncontested and merged quickly.

KEP Editor Role

Taking a cue from the Python PEP process, we define the role of a KEP editor. The job of an KEP editor is likely very similar to the PEP editor responsibilities and will hopefully provide another opportunity for people who do not write code daily to contribute to Kubernetes.

In keeping with the PEP editors, who:

Read the PEP to check if it is ready: sound and complete. The ideas must make technical sense, even if they don't seem likely to be accepted. The title should accurately describe the content. Edit the PEP for language (spelling, grammar, sentence structure, etc.), markup (for reST PEPs), code style (examples should match PEP 8 & 7)

KEP editors should generally not pass judgement on a KEP beyond editorial corrections. KEP editors can also help inform authors about the process and otherwise help things move smoothly.

Important Metrics

It is proposed that the primary metrics that would signal the success or failure of the KEP process are:

  • how many "enhancements" are tracked with a KEP
  • distribution of time a KEP spends in each state
  • KEP rejection rate
  • PRs referencing a KEP merged per week
  • number of issues open which reference a KEP
  • number of contributors who authored a KEP
  • number of contributors who authored a KEP for the first time
  • number of orphaned KEPs
  • number of retired KEPs
  • number of superseded KEPs

Prior Art

The KEP process, as proposed, was essentially stolen from the Rust RFC process which itself resembles the Python PEP process.

Drawbacks

Any additional process has the potential to engender resentment within the community. There is also a risk that the KEP process as designed will not sufficiently address the scaling challenges we face today. PR review bandwidth is already at a premium, and we may find that the KEP process introduces an unreasonable bottleneck on our development velocity.

It certainly can be argued that the lack of a dedicated issue/defect tracker beyond GitHub issues contributes to our challenges in managing a project as large as Kubernetes. However, given that other large organizations, including GitHub itself, make effective use of GitHub issues, perhaps the argument is overblown.

The centrality of Git and GitHub within the KEP process also may place too high a barrier to potential contributors. However, given that both Git and GitHub are required to contribute code changes to Kubernetes today, perhaps it would be reasonable to invest in providing support to those unfamiliar with this tooling.

Expanding the proposal template beyond the single-sentence description currently required in the features issue template may be a heavy burden for non-native English speakers. Here, the role of the KEP editor, combined with kindness and empathy, will be crucial to making the process successful.

Alternatives

This KEP process is related to:

this proposal attempts to place these concerns within a general framework.

GitHub Issues vs. KEPs

The use of GitHub issues when proposing changes does not provide SIGs good facilities for signaling approval or rejection of a proposed change to Kubernetes, because anyone can open a GitHub issue at any time. Additionally, managing a proposed change across multiple releases is somewhat cumbersome as labels and milestones need to be updated for every release that a change spans. These long-lived GitHub issues lead to an ever-increasing number of issues open against kubernetes/features, which itself has become a management problem.

In addition to the challenge of managing issues over time, searching for text within an issue can be challenging. The flat hierarchy of issues can also make navigation and categorization tricky. Not all community members will be uncomfortable using Git directly, but it is imperative for our community to educate people on a standard set of tools so they can take their experience to other projects they may decide to work on in the future. While git is a fantastic version control system (VCS), it is neither a project management tool nor a cogent way of managing an architectural catalog or backlog. This proposal is limited to motivating the creation of a standardized definition of work in order to facilitate project management. This primitive for describing a unit of work may also allow contributors to create their own personalized view of the state of the project while relying on Git and GitHub for consistency and durable storage.

Unresolved Questions

  • How reviewers and approvers are assigned to a KEP
  • Example schedule, deadline, and time frame for each stage of a KEP
  • Communication/notification mechanisms
  • Review meetings and escalation procedure