community/contributors/devel/development.md

# Development Guide

This document is the canonical source of truth for things like
supported toolchain versions for building Kubernetes.

Please submit an [issue] on github if you 
* find a requirement that this doc does not capture,
* find other docs with references to requirements that
  are not simply links to this doc.

This document is intended to be relative to the branch in which it is found.

Development branch requirements will change over time, but release branch
requirements are frozen.

## Pre submit flight checks

Make sure you decide whether your issue and/or pull request is improving kubernetes architecture or whether its simply fixing a bug.

Make sure there are no typos, if you need a diagram, add it.  Make sure you SEPARATE the description of the problem
(i.e. Y is a critical component that is too slow for an SLA that we care about) from the solution (i.e. make X faster).

Some of these checks were less common in Kubernetes earlier days, but now having over 1000 contributors, each issue should be
filed with care, and should be sanity-checkable in under 5 minutes (even the busiest of reviewers can spare up to 5 minutes to
review a patch that is thoughtfully justified).

### Is this just a simple bug fix?

These patches can be easy to review since test coverage is submitted with the patch.  Bug fixes don't usually require alot
of extra testing: But please update the unit tests so that they catch the bug !

### Is this an architecture improvement?

Some examples of "Architecture" improvements:

- Adding a new feature or making a feature more configurable/modular.
- Converting structs to interfaces.
- Improving test coverage.
- Decoupling logic or creation of new utilities.
- Making code more resilient (sleeps, backoffs, reducing flakiness, etc).

These sorts of improvements are easily evaluated if they decrease lines of code without breaking functionality.

If you are improving the quality of code, then justify/state exactly what you 'cleaning up' in your Pull Request so as
not to waste reviewer time.

If you're making code more resilient, test it with a local cluster to demonstrate how exactly your patch changes
things.

Example: If you made a controller more robust to inconsistent data, make a mock object which returns incorrect data a
few times and verify the controllers behaviour accordingly.

### Is this a performance improvement ?

If you are submitting a performance bug, you MUST ALSO submit data that demonstrates your problem if you want the issue to
remain open.  This can be done locally using kubemark, scheduler_perf, unit tests, go benchmark tests, or e2e tests on
a real cluster with metrics plots.

Examples of how NOT to suggest a performance bug (these can really lead to a long review process and waste cycles):

- We *should* be doing X instead of Y because it *might* lead to better performance.
- Doing X instead of Y would reduce calls to Z.

The above statements have basically no value to a reviewer, because neither is a strong, testable, assertive statement.
This will land your PR in a no-man's-land zone (at best), or waste tons of time for a busy reviewer (at worst).

Of course any improvement is welcome, but performance improvements are the hardest to review.  They often make code more
complex, and to-often are not easily evaluated at review time due to lack of sufficient data submitted by the author
of a performance improvement patch.

Some examples of "Performance" improvements:

- Improving a caching implementation.
- Reducing calls to functions which are O(n^2), or reducing dependence on API server requests.
- Changing the value of default parameters for proceeses, or making those values 'smarter'.
- Parallelizing a calculation that needs to run on a large set of node/pod objects.

These issues should always be submitted with (in decreasing order or value):

- A golang Benchmark test.
- A visual depiction of reduced metric load on a cluster (measurable using metrics/ endpoints and grafana).
- A hand-instrumented timing test (i.e. adding some logs into the controller manager).

Without submitting data and results for your suggested performance improvements, its very possible that bikeshedding
about meaningless possible performance optimizations could waste both reviewer time as well as your own.

Some examples of properly submitted performance issues, from different parts of the codebase.  They all have one thing
in common: Lots of data in the issue definition.  If you are new to kubernetes and thinking about filing a performance
optimization, re-read one or all of these before you get started.

- https://github.com/kubernetes/kubernetes/issues/18266 (apiserver)
- https://github.com/kubernetes/kubernetes/issues/32833 (node)
- https://github.com/kubernetes/kubernetes/issues/31795 (scheduler)

Since performance improvements deal with empirical systems, one playing in this space should be intimately familiar with
the "scientific method" of creating a hypothesis, collecting data, and then revising your hypothesis.  The above issues
tend to do this transparently, using figures and data rather then theoretical postulations, as a first pass before a
single line of code is reviewed.

## Building Kubernetes with Docker

Official releases are built using Docker containers. To build Kubernetes using Docker please follow 
[these instructions](http://releases.k8s.io/HEAD/build/README.md).

## Building Kubernetes on a local OS/shell environment

Kubernetes development helper scripts assume an up-to-date
GNU tools environment. Most recent Linux distros should work
out-of-the-box.

Mac OS X ships with outdated BSD-based tools.
We recommend installing [Os X GNU tools].

### etcd

Kubernetes maintains state in [`etcd`][etcd-latest], a distributed key store.

Please [install it locally][etcd-install] to run local integration tests.

### Go

Kubernetes is written in [Go](http://golang.org).
If you don't have a Go development environment,
please [set one up](http://golang.org/doc/code.html).


| Kubernetes     | requires Go  |
|----------------|--------------|
| 1.0 - 1.2      | 1.4.2        |
| 1.3, 1.4       | 1.6          |
| 1.5 and higher | 1.7 - 1.7.5  |
| | [1.8][go-1.8] not verified as of Feb 2017 |

After installation, you'll need `GOPATH` defined,
and `PATH` modified to access your Go binaries.

A common setup is
```sh
export GOPATH=$HOME/go
export PATH=$PATH:$GOPATH/bin
```

#### Upgrading Go 

Upgrading Go requires specific modification of some scripts and container
images.

- The image for cross compiling in [build/build-image/cross].
  The `VERSION` file and `Dockerfile`.
- Update [dockerized-e2e-runner.sh] to run a kubekins-e2e with the desired Go version.
  This requires pushing the [e2e][e2e-image] and [test][test-image] images that are `FROM` the desired Go version.
- The cross tag `KUBE_BUILD_IMAGE_CROSS_TAG` in [build/common.sh].


#### Dependency management

Kubernetes build/test scripts use [`godep`](https://github.com/tools/godep) to
manage dependencies.

```sh
go get -u github.com/tools/godep
```

Check your version; `v63` or higher is known to work for Kubernetes.
```sh
godep version
```

Developers planning to manage dependencies in the `vendor/` tree may want to
explore alternative environment setups. See [using godep to manage dependencies](godep.md).



## Workflow

![Git workflow](git_workflow.png)

### 1 Fork in the cloud

1. Visit https://github.com/kubernetes/kubernetes
2. Click `Fork` button (top right) to establish a cloud-based fork.

### 2 Clone fork to local storage

Per Go's [workspace instructions][go-workspace], place Kubernetes' code on your
`GOPATH` using the following cloning procedure.

Define a local working directory:

```sh
# If your GOPATH has multiple paths, pick
# just one and use it instead of $GOPATH here
working_dir=$GOPATH/src/k8s.io
```

> If you already do Go development on github, the `k8s.io` directory
> will be a sibling to your existing `github.com` directory.

Set `user` to match your github profile name:

```sh
user={your github profile name}
```

Both `$working_dir` and `$user` are mentioned in the figure above.

Create your clone:

```sh
mkdir -p $working_dir
cd $working_dir
git clone https://github.com/$user/kubernetes.git
# or: git clone git@github.com:$user/kubernetes.git

cd $working_dir/kubernetes
git remote add upstream https://github.com/kubernetes/kubernetes.git
# or: git remote add upstream git@github.com:kubernetes/kubernetes.git

# Never push to upstream master
git remote set-url --push upstream no_push

# Confirm that your remotes make sense:
git remote -v
```

#### Define a pre-commit hook

Please link the Kubernetes pre-commit hook into your `.git` directory.

This hook checks your commits for formatting, building, doc generation, etc.
It requires both `godep` and `etcd` on your `PATH`.

```sh
cd $working_dir/kubernetes/.git/hooks
ln -s ../../hooks/pre-commit .
```

### 3 Branch

Get your local master up to date:

```sh
cd $working_dir/kubernetes
git fetch upstream
git checkout master
git rebase upstream/master
```

Branch from it:
```sh
git checkout -b myfeature
```

Then edit code on the `myfeature` branch.

#### Build

```sh
cd $working_dir/kubernetes
make
```

To remove the limit on the number of errors the Go compiler reports (default limit is 10 errors):
```sh
make GOGCFLAGS="-e"
```

To build with optimizations disabled for enabling use of source debug tools:

```sh
make GOGCFLAGS="-N -l"
```

To build binaries for all platforms:

```sh
make cross
```

#### Test

```sh
cd $working_dir/kubernetes

# Run every unit test
make test 

# Run package tests verbosely
make test WHAT=pkg/util/cache GOFLAGS=-v

# Run integration tests, requires etcd
make test-integration

# Run e2e tests
make test-e2e
```

See the [testing guide](testing.md) and [end-to-end tests](e2e-tests.md)
for additional information and scenarios.

### 4 Keep your branch in sync

```sh
# While on your myfeature branch
git fetch upstream
git rebase upstream/master
```

### 5 Commit

Commit your changes.

```sh
git commit
```
Likely you go back and edit/build/test some more then `commit --amend`
in a few cycles.

### 6 Push

When ready to review (or just to establish an offsite backup or your work),
push your branch to your fork on `github.com`:

```sh
git push -f origin myfeature
```

### 7 Create a pull request

1. Visit your fork at https://github.com/$user/kubernetes (replace `$user` obviously).
2. Click the `Compare & pull request` button next to your `myfeature` branch.
3. Check out the pull request [process](pull-requests.md) for more details.

_If you have upstream write access_, please refrain from using the GitHub UI for
creating PRs, because GitHub will create the PR branch inside the main
repository rather than inside your fork.

#### Get a code review

Once your pull request has been opened it will be assigned to one or more
reviewers.  Those reviewers will do a thorough code review, looking for
correctness, bugs, opportunities for improvement, documentation and comments,
and style.

Commit changes made in response to review comments to the same branch on your
fork.

Very small PRs are easy to review.  Very large PRs are very difficult to
review.

At the assigned reviewer's discretion, a PR may be switched to use
[Reviewable](https://reviewable.k8s.io) instead.  Once a PR is switched to
Reviewable, please ONLY send or reply to comments through reviewable.  Mixing
code review tools can be very confusing.

See [Faster Reviews](faster_reviews.md) for some thoughts on how to streamline
the review process.


#### Squash and Merge

Upon merge (by either you or your reviewer), all commits left on the review
branch should represent meaningful milestones or units of work.  Use commits to
add clarity to the development and review process.

Before merging a PR, squash any _fix review feedback_, _typo_, and _rebased_
sorts of commits. 

It is not imperative that every commit in a PR compile and pass tests
independently, but it is worth striving for.

For mass automated fixups (e.g. automated doc formatting), use one or more
commits for the changes to tooling and a final commit to apply the fixup en
masse. This makes reviews easier.

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[Os X GNU tools]: https://www.topbug.net/blog/2013/04/14/install-and-use-gnu-command-line-tools-in-mac-os-x
[build/build-image/cross]: https://github.com/kubernetes/kubernetes/blob/master/build/build-image/cross
[build/common.sh]: https://github.com/kubernetes/kubernetes/blob/master/build/common.sh
[dockerized-e2e-runner.sh]: https://github.com/kubernetes/test-infra/blob/master/jenkins/dockerized-e2e-runner.sh
[e2e-image]: https://github.com/kubernetes/test-infra/tree/master/jenkins/e2e-image
[etcd-latest]: https://coreos.com/etcd/docs/latest
[etcd-install]: testing.md#install-etcd-dependency
<!-- https://github.com/coreos/etcd/releases -->
[go-1.8]: https://blog.golang.org/go1.8
[go-workspace]: https://golang.org/doc/code.html#Workspaces
[issue]: https://github.com/kubernetes/kubernetes/issues
[kubectl user guide]: https://kubernetes.io/docs/user-guide/kubectl
[kubernetes.io]: https://kubernetes.io
[mercurial]: http://mercurial.selenic.com/wiki/Download
[test-image]: https://github.com/kubernetes/test-infra/tree/master/jenkins/test-image