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Merge pull request #873 from spiffxp/owners 

Rewrite OWNERS docs
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# Owners files
_Note_: This is a design for a feature that is not yet implemented. See the [contrib PR](https://github.com/kubernetes/contrib/issues/1389) for the current progress.
# OWNERS files
## Overview
We want to establish owners for different parts of the code in the Kubernetes codebase. These owners
will serve as the approvers for code to be submitted to these parts of the repository. Notably, owners
are not necessarily expected to do the first code review for all commits to these areas, but they are
required to approve changes before they can be merged.
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](https://chromium.googlesource.com/chromium/src/+/master/docs/code_reviews.md), which in turn
inspired [GitHub's CODEOWNERS files](https://help.github.com/articles/about-codeowners/).
**Note** The Kubernetes project has a hiatus on adding new approvers to OWNERS files. At this time we are [adding more reviewers](https://github.com/kubernetes/kubernetes/pulls?utf8=%E2%9C%93&q=is%3Apr%20%22Curating%20owners%3A%22%20) to take the load off of the current set of approvers and once we have had a chance to flush this out for a release we will begin adding new approvers again. Adding new approvers is planned for after the Kubernetes 1.6.0 release.
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
## High Level flow
## OWNERS spec
### Step One: A PR is submitted
The [mungegithub gitrepos
feature](https://github.com/kubernetes/test-infra/blob/master/mungegithub/features/repo-updates.go)
is the main consumer of OWNERS files. If this page is out of date, look there.
After a PR is submitted, the automated kubernetes PR robot will append a message to the PR indicating the owners
that are required for the PR to be submitted.
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.
Subsequently, a user can also request the approval message from the robot by writing:
OWNERS files are in YAML format and support the following keys:
- `approvers`: a list of GitHub usernames or aliases that can `/approve` a PR
- [DEPRECATED] `assignees`: do not use, equivalent to `approvers`
([kubernetes/test-infra#3851](https://github.com/kubernetes/test-infra/issues/3851))
- `labels`: a list of GitHub labels to automatically apply to a PR
- `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:
```
@k8s-bot approvers
approvers:
- alice
- bob # this is a comment
reviewers:
- alice
- carol # this is another comment
- sig-foo # this is an alias
```
into a comment.
Each repo may contain at its root an OWNERS_ALIAS file.
In either case, the automation replies with an annotation that indicates
the owners required to approve. The annotation is a comment that is applied to the PR.
This comment will say:
OWNERS_ALIAS files are in YAML format and support the following keys:
```
Approval is required from <owner-a> OR <owner-b>, AND <owner-c> OR <owner-d>, AND ...
- `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
```
The set of required owners is drawn from the OWNERS files in the repository (see below). For each file
there should be multiple different OWNERS, these owners are listed in the `OR` clause(s). Because
it is possible that a PR may cover different directories, with disjoint sets of OWNERS, a PR may require
approval from more than one person, this is where the `AND` clauses come from.
## Code Review Process
`<owner-a>` should be the github user id of the owner _without_ a leading `@` symbol to prevent the owner
from being cc'd into the PR by email.
This is a simplified description of our [full PR testing and merge
workflow](https://github.com/kubernetes/community/blob/master/contributors/devel/pull-requests.md#the-testing-and-merge-workflow)
that conveniently forgets about the existence of tests, to focus solely on the roles driven by
OWNERS files.
### Step Two: A PR is LGTM'd
- The **author** submits a PR
- Phase 0: Automation determines **reviewers** and **approvers** for the PR
- Determine the set of OWNERS files nearest to the code being changed
- Choose two **reviewers**, and assign them to the PR (choose more than one to avoid assigning to
an inactive / unavailable reviewer)
- 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.
- The PR **author** cannot be their own **reviewer**
- 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](https://github.com/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")
- The PR **author** can be their own **approver** (assuming they are listed in the appropriate
OWNERS files)
- **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`
- `mungegithub` ([@k8s-merge-robot](https://github.com/k8s-merge-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,
`mungegithub` ([@k8s-merge-robot](https://github.com/k8s-merge-robot/)) applies an `approved`
label
- Phase 3: Automation merges the PR
- All required labels are present (eg: `lgtm`, `approved`)
- All required status checks for the PR are verified as green
- The PR is merged
Once a PR is reviewed and LGTM'd it is eligible for submission. However, for it to be submitted
an owner for all of the files changed in the PR have to 'approve' the PR. A user is an owner for a
file if they are included in the OWNERS hierarchy (see below) for that file.
## Quirks of the Process
Owner approval comes in two forms:
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 owner adds a comment to the PR saying "I approve" or "approved"
* An owner is the original author of the PR
- 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 **approves)
- 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](https://k8s-gubernator.appspot.com/pr)
- 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)
## Implementation
In the case of a comment based approval, the same rules as for the 'lgtm' label apply. If the PR is
changed by pushing new commits to the PR, the previous approval is invalidated, and the owner(s) must
approve again. Because of this is recommended that PR authors squash their PRs prior to getting approval
from owners.
### [`mungegithub`](https://github.com/kubernetes/test-infra/tree/master/mungegithub)
### Step Three: A PR is merged
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.
Once a PR is LGTM'd and all required owners have approved, it is eligible for merge. The merge bot takes care of
the actual merging.
- [feature:
gitrepos](https://github.com/kubernetes/test-infra/blob/master/mungegithub/features/repo-updates.go)
- responsible for parsing OWNERS and OWNERS_ALIAS files
- if its `use-reviewers` flag is set to false, **approvers** will also be **reviewers**
- if its `enable-md-yaml` flag is set, `.md` files will also be parsed to see if they have
embedded OWNERS content (this is only used by
[kubernetes.github.io](https://github.com/kubernetes/kubernetes.github.io/))
- used by other mungers to get the set of **reviewers** or **approvers** for a given path
- [munger:
blunderbuss](https://github.com/kubernetes/test-infra/blob/master/mungegithub/mungers/blunderbuss.go)
- responsible for determining **reviewers** and assigning to them
- chooses from people in the deepest/closest OWNERS files to the code being changed
- weights its choice based on the magnitude of lines changed for each file
- randomly chooses to ensure the same people aren't chosen every time
- if its `blunderbuss-number-assignees` flag is unset, it will default to 2 assignees
- [munger:
approval-handler](https://github.com/kubernetes/test-infra/blob/master/mungegithub/mungers/approval-handler.go)
- responsible for adding the `approved` label once an **approver** for each of the required
OWNERS files has `/approve`'d
- responsible for commenting as required OWNERS files are satisfied
- responsible for removing outdated approval status comments
- [full description of the
algorithm](https://github.com/kubernetes/test-infra/blob/6f5df70c29528db89d07106a8156411068518cbc/mungegithub/mungers/approval-handler.go#L99-L111)
- [munger:
submit-queue](https://github.com/kubernetes/test-infra/blob/master/mungegithub/mungers/submit-queue.go)
- 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)
## Design details
### [`prow`](https://github.com/kubernetes/test-infra/tree/master/prow)
We need to build new features into the existing github munger in order to accomplish this. Additionally
we need to add owners files to the repository.
Prow receives events from GitHub, and reacts to them. It is effectively stateless.
### Approval Munger
- [plugin: lgtm](https://github.com/kubernetes/test-infra/tree/master/prow/plugins/lgtm)
- responsible for adding the `lgtm` label when a **reviewer** comments `/lgtm` on a PR
- the **PR author** may not `/lgtm` their own PR
- [plugin: assign](https://github.com/kubernetes/test-infra/tree/master/prow/plugins/assign)
- responsible for assigning GitHub users in response to `/assign` comments on a PR
- responsible for unassigning GitHub users in response to `/unassign` comments on a PR
We need to add a munger that adds comments to PRs indicating whose approval they require. This munger will
look for PRs that do not have approvers already present in the comments, or where approvers have been
requested, and add an appropriate comment to the PR.
### GitHub
GitHub provides a few integration points for our automation:
- [Status Checks](https://help.github.com/articles/about-required-status-checks/): our tests and
submit queue use these to communicate whether a commit is OK
- [Protected Branches](https://help.github.com/articles/about-protected-branches/): ensure that a
branch cannot be merged unless all status checks are green
- [Merge Button](https://developer.github.com/v3/pulls/#merge-a-pull-request-merge-button): the
submit queue effectively uses an API driven click of this button
### Status Munger
## Updating OWNERS
GitHub has a [status api](https://developer.github.com/v3/repos/statuses/), we will add a status munger that pushes a status onto a PR of approval status. This status will only be approved if the relevant
approvers have approved the PR.
OWNERS files should be regularly maintained.
### Requiring approval status
We should strive to:
Github has the ability to [require status checks prior to merging](https://help.github.com/articles/enabling-required-status-checks/)
- 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
Once we have the status check munger described above implemented, we will add this required status check
to our main branch as well as any release branches.
Bad examples of OWNERS usage:
### Adding owners files
- 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
In each directory in the repository we may add an OWNERS file. This file will contain the github OWNERS
for that directory. OWNERSHIP is hierarchical, so if a directory does not container an OWNERS file, its
parent's OWNERS file is used instead. There will be a top-level OWNERS file to back-stop the system.
Good examples of OWNERS usage:
Obviously changing the OWNERS file requires OWNERS permission.
<!-- BEGIN MUNGE: GENERATED_ANALYTICS -->
[![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/docs/devel/owners.md?pixel)]()
<!-- END MUNGE: GENERATED_ANALYTICS -->
- 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)