Making kubectl plugins mainstream

It's the end of 2019 and kubectl plugins are finally gaining steam. Krew plugin manager for kubectl (https://krew.dev) is now hosting over 60 plugins (doubling every 6 months).
This talk is an introduction to kubectl plugin mechanism, and best practices for developing plugins.

Presented at KubeCon 2019 North America, San Diego, CA by @ahmetb.

Transcript

1. @ahmetb
   making
   kubectl plugins
   mainstream
   ahmet alp balkan (@ahmetb)
   google cloud
   

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2. @ahmetb
   @ahmetb on {twitter, github}
   ➔ ported docker.exe, docker maintainer ~2015
   ➔ started Azure Container Registry ~2016
   ➔ developer advocate @ Google ~2017
   working on Google Cloud Run, Knative, dev tools
   ➔ kubectx & kubens & kubectl-aliases
   ➔ Google’s microservices-demo
   ➔ kubectl plugin manager krew.dev
   about me
   2
   

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3. @ahmetb
   agenda
   1. kubectl plugins 101
   2. krew (plugin manager) overview
   3. why did we need plugins?
   4. let's develop a plugin
   5. plugin runtime
   6. why develop a plugin?
   7. how to distribute your plugins
   8. best practices for writing plugins
   user
   developer
   3
   

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4. @ahmetb
   USING
   PLUGINS
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5. @ahmetb
   kubectl plugins
   circa v1.12
   an extension mechanism
   that lets you write
   your own kubectl subcommands.
   5
   

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6. @ahmetb
   kubectl plugin mechanism
   in a nutshell
   1. write an executable program
   2. name it kubectl-something
   3. put it in your $PATH
   4. invoke as "kubectl something"
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7. @ahmetb
   where do I
   find plugins?
   - github?
   - some list?
   - package manager?
   7
   

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8. @ahmetb
   Krew
   the missing plugin manager for kubectl
   Kubernetes SIG CLI sub-project
   https://krew.dev
   (sigs.k8s.io/krew)
   8
   

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9. @ahmetb
   What is Krew?
   - Functionality
   - discover plugins
   - install plugins
   - update plugins
   - remove plugins
   - Started in 2018 as an intern project at Google Cloud.
   - Donated to Kubernetes project in May 2019.
   - Not an actual package manager
   - Doesn't handle dependencies.
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10. @ahmetb
    kubectl plugins on Krew
    KubeCon 2018 Seattle
    Today
    KubeCon 2019 EU
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11. @ahmetb
    kubectl plugins on Krew
    KubeCon 2018 Seattle
    Today
    KubeCon 2019 EU
    11
    

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12. @ahmetb
    demo: let's try
    krew
    12
    

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13. @ahmetb
    why did we need
    kubectl plugins?
    13
    

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14. @ahmetb
    1.
    people want to add
    new sub-commands
    to kubectl
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15. @ahmetb
    15
    

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16. @ahmetb
    2.
    everybody has
    opinions
    16
    

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17. @ahmetb
    17
    

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18. @ahmetb
    3.
    reaching consensus
    in open source
    is not trivial
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19. @ahmetb
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20. @ahmetb
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21. @ahmetb
    4.
    we cannot solve
    everything in the
    kubernetes core
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22. @ahmetb
    Storage plugins
    Network plugins
    Custom controllers
    Scheduler extension/
    custom scheduler
    Custom resources (CRD)
    API Access Extensions
    (Admission webhooks,
    authentication webhook,
    authz/RBAC webhooks)
    kubernetes.io/docs/concepts/extend-kubernetes/extend-cluster
    Kubectl Plugins
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23. @ahmetb
    5.
    kubernetes core
    moves slower
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24. @ahmetb
    official command plugin
    KEP + approval no approvals
    usefulness and stability no restrictions
    hosted in kubectl codebase
    (Go only)
    any language
    tied to Kubernetes release cycle release at your own pace
    has to be consistent with kubectl has room for creativity
    takes O(months)..O(years)
    from alpha→beta→stable
    develop & distribute
    in O(hours)
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25. @ahmetb
    6.
    people are
    creative
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26. @ahmetb
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27. @ahmetb
    ...even GUI-based plugins
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28. @ahmetb
    7.
    allow safe
    experimentation
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29. @ahmetb
    ➔ deprecating a kubectl command is painful.
    ➔ let people experiment, graduate successful ones.
    experimentation
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30. @ahmetb
    DEVELOPING
    PLUGINS
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31. @ahmetb
    kubectl plugin mechanism
    in a nutshell
    1. write an executable program
    2. name it kubectl-something
    3. put it in your $PATH
    4. invoke as "kubectl something"
    31
    

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32. @ahmetb
    demo: let's develop a plugin!
    git.k8s.io/sample-cli-plugin
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33. @ahmetb
    "kubectl a b c"
    → is "a" builtin command?
    → kubectl-a-b-c ?
    → kubectl-a-b ?
    → kubectl-a ?
    plugin lookup
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34. @ahmetb
    plugin execution runtime
    1. look for the plugin executable in PATH
    2. execve() syscall
    replace kubectl with the plugin process
    ◆ inherit environment variables
    ◆ inherit standard streams
    ◆ determine exitcode of kubectl invocation
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35. @ahmetb
    why develop a kubectl plugin?
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36. @ahmetb
    your tool has a weird name
    and it's not very memorable
    rakkess kubectl access-matrix
    ketall kubectl get-all
    ksort kubectl sort-manifests
    kail kubectl tail
    feels more natural
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37. @ahmetb
    kubectl is missing a feature
    37
    

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38. @ahmetb
    kubectl is missing a feature
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39. @ahmetb
    kubectl is missing a feature
    39
    

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40. @ahmetb
    address shortcomings of kubectl
    kubectl get all:
    lies to you
    plugin: tells you the truth
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41. @ahmetb
    enhances existing kubectl command
    builtin: query one
    resource at a time
    plugin: shows a matrix
    of all capabilities
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42. @ahmetb
    enhances existing kubectl command
    plugin: queries for all
    subjects in the cluster
    builtin: query one
    user at a time
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43. @ahmetb
    so you have a
    plugin, now what?
    ➔ packaging
    ➔ distribution
    ➔ release
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44. @ahmetb
    plugin developer problems
    ● How can people hear about my plugin?
    ● How can I package my plugin for others to install?
    ● How can I deliver updates?
    If you're a kubectl plugin developer,
    Krew solves these problems.
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45. @ahmetb
    packaging/distribution
    user
    plugin
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46. @ahmetb
    packaging/distribution
    macOS
    windows
    linux
    Chocolatey
    Homebrew
    MacPorts
    apt
    yum/dnf
    pacman
    apk
    ...
    user
    plugin
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47. @ahmetb
    Krew to rescue!
    user
    plugin
    Krew
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48. @ahmetb
    Without krew
    https://github.com/guessi/kubectl-grep
    how to update?
    how to uninstall?
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49. @ahmetb
    ...users to:
    ● install plugins
    ● keep them up to date
    ● remove plugins cleanly
    ...developers to:
    ● make their plugins discoverable by users
    ● package their plugins for multiple platforms
    ● deliver updates
    Krew helps...
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50. @ahmetb
    Krew currently operates with a
    centralized package index.
    sigs.k8s.io/krew-index
    centralized discovery
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51. @ahmetb
    packaging & distributing with Krew
    1. make your plugin available as a .tar.gz or .zip archive
    2. write a plugin manifest
    3. submit a pull request to krew-index
    4. party!
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52. @ahmetb
    plugin manifest
    apiVersion: krew.googlecontainertools.github.com/v1alpha2
    kind: Plugin
    metadata:
    name: "access-matrix"
    spec:
    version: "v0.4.0"
    homepage: "https://github.com/corneliusweig/rakkess"
    platforms:
    -
    -
    -
    - ...
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53. @ahmetb
    ... # continued
    spec:
    platforms:
    - selector:
    matchLabels:
    os: linux
    arch: amd64
    uri: https://github.com/corneliusweig/rakkess/releases/v0.4.0/bundle.tar.gz
    sha256: 7a16c61dfc4e2924fdedc894d59db7820bc4643a58d9a853c4eb83eadd4deee8
    files:
    - from: ./rakkess_linux-amd64
    to: ./rakkess
    - from: ./LICENSE
    to: "."
    bin: ./rakkess
    plugin manifest - platform
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54. @ahmetb
    recipes for success
    1. name your plugin for clarity
    (see Krew Naming Guide)
    2. reuse flags/options and KUBECONFIG detection from
    k8s.io/cli-runtime/pkg/genericclioptions
    3. import auth plugins for cloud clusters
    import _ "k8s.io/client-go/plugin/pkg/client/auth"
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55. @ahmetb
    wrap up
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56. @ahmetb
    Join us make kubectl plugins better!
    ● Become a kubectl plugin developer,
    submit your plugins to Krew.dev.
    ● Join developing the Krew project.
    ○ you don’t need to be a Kubernetes expert
    ○ clean and young codebase
    ○ low bug count, high creativity
    ● Bring your ideas to Kubernetes SIG CLI.
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57. @ahmetb
    thanks!
    sigs.k8s.io/krew
    git.k8s.io/sample-cli-plugin
    twitter.com/ahmetb
    github.com/ahmetb
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