development

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 * Notice a requirement that this doc does not capture. * Find a different doc that specifies requirements (the doc should instead link here).

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

Pre submit flight checks

Determine whether your issue or pull request is improving Kubernetes’ architecture or whether it’s simply fixing a bug.

If you need a diagram, add it. SEPARATE the description of the problem (e.g. Y is a critical component that is too slow for an SLA that we care about) from the solution (e.g. make X faster).

Some of these checks were less common in Kubernetes’ earlier days. Now that we have over 1000 contributors, each issue should be filed with care. No issue should take more than 5 minutes to check for sanity (even the busiest of reviewers can spare 5 minutes to review a patch that is thoughtfully justified).

Is this just a simple bug fix?

Simple bug patches are easy to review since test coverage is submitted with the patch. Bug fixes don’t usually require a lot of extra testing, but please update the unit tests so they catch the bug!

Is this an architecture improvement?

Some examples of “Architecture” improvements include:

  • Adding a new feature or making a feature more configurable or modular.
  • 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, especially when they decrease lines of code without breaking functionality. That said, please explain exactly what you are ‘cleaning up’ in your Pull Request so as not to waste a reviewer’s time.

If you’re making code more resilient, include tests that demonstrate the new resilient behavior. For example: if your patch causes a controller to better handle inconsistent data, make a mock object which returns incorrect data a few times and verify the controller’s new behaviour.

Is this a performance improvement ?

Performance bug reports MUST include data that demonstrates the bug. Without data, the issue will be closed. You can measure performance using kubemark, scheduler_perf, go benchmark tests, or e2e tests on a real cluster with metric plots.

Examples of how NOT to suggest a performance bug (these 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 no value to a reviewer because neither is backed by data. Writing issues like this lands your PR in a no-man’s-land and waste your reviewers’ time.

Examples of possible performance improvements include (remember, you MUST document the improvement with data):

  • Improving a caching implementation.
  • Reducing calls to functions which are O(n^2)
  • Reducing dependence on API server requests.
  • Changing the value of default parameters for processes, 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 of 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).

Here are some examples of properly submitted performance issues. If you are new to kubernetes and thinking about filing a performance optimization, re-read one or all of these before you get started.

Since performance improvements can be empirically measured, you should follow the “scientific method” of creating a hypothesis, collecting data, and then revising your hypothesis. The above issues do this transparently, using figures and data rather then conjecture. Notice that the problem is analyzed and a correct solution is created 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.

Building Kubernetes on a local OS/shell environment

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

macOS ships with outdated BSD-based tools. We recommend installing macOS GNU tools.

etcd

Kubernetes maintains state in etcd, a distributed key store.

Please install it locally to run local integration tests.

Go

Kubernetes is written in Go. If you don’t have a Go development environment, please set one up.

Kubernetes requires Go
1.0 - 1.2 1.4.2
1.3, 1.4 1.6
1.5, 1.6 1.7 - 1.7.5
1.7 1.8.1
1.8 1.8.3
1.9 1.9.1
1.10 1.9.1
1.11+ 1.10.2

Ensure your GOPATH and PATH have been configured in accordance with the Go environment instructions.

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 the desired Go version in Dockerfile for the e2e and test. This requires pushing the e2e and test images that are FROM the desired Go version.
  • The cross tag KUBE_BUILD_IMAGE_CROSS_TAG in build/common.sh.

Dependency management

Kubernetes uses godep to manage dependencies.

Developers who need to manage dependencies in the vendor/ tree should read the docs on using godep to manage dependencies.

Build with Bazel/Gazel

Building with Bazel is currently experimental. For more information, see Build with Bazel.

GitHub workflow

To check out code to work on, please refer to this guide.