Should Kubernetes have a DSL for configuration?

Slides used for the introduction to my Birds of a Feather session at KubeCon EU in Berlin. A discussion of various approaches to using programming languages to configure Kubernetes rather than writing the raw data.

Transcript

1. (without introducing more risk)
   Should Kubernetes
   have a DSL?
   Puppet
   Gareth Rushgrove
   Alternative configuration options for K8
   

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2. (without introducing more risk)
   @garethr
   

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3. (without introducing more risk)
   Gareth Rushgrove
   

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4. (without introducing more risk)
   What we’ll cover
   This session
   

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5. - Setting the scene
   - Open discussion
   - Summary
   Gareth Rushgrove
   

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6. (without introducing more risk)
   The argument
   Why not (only) YAML
   

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7. Gareth Rushgrove
   Brian Grant, Google, Kubernetes Config SIG
   “We've had a few complaints that YAML is
   ugly, error prone, hard to read, etc. Are
   there any other alternatives we might want
   to support?
   

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8. Gareth Rushgrove
   

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9. (without introducing more risk)
   Gareth Rushgrove
   API wire format as user interface
   template:
   metadata:
   labels:
   app: guestbook
   tier: frontend
   spec:
   containers:
   - name: php-redis
   image: gcr.io/google_samples/gb-frontend:v4
   resources:
   requests:
   cpu: 100m
   memory: 100Mi
   env:
   

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10. The language to represent the data should
    be a simple, data-only format such as JSON
    or YAML, and programmatic modification of
    this data should be done in a real
    programming language
    Gareth Rushgrove
    Borg, Omega, and Kubernetes, ACM Queue, Volume 14, issue 1 http://queue.acm.org/detail.cfm?id=2898444
    “
    

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11. The reality is probably closer to most people
    hand writing YAML files
    Gareth Rushgrove
    

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12. Code allows us to
    - Avoid repetition
    - Combine external inputs
    - Enforce correctness
    - Introduce abstractions
    Gareth Rushgrove
    

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13. (without introducing more risk)
    Configuration language for JSON data
    Jsonnet
    

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14. (without introducing more risk)
    jsonnet.org
    

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15. (without introducing more risk)
    kubernetes examples
    

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16. (without introducing more risk)
    kubecfg
    

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17. (without introducing more risk)
    Gareth Rushgrove
    Jsonnet template
    $ cat squid.jsonnet
    local squid = {
    namespace:: "squid",
    squid_service: kube.Service("proxy") {
    metadata+: { namespace: $.namespace },
    target_pod: $.squid.spec.template,
    port: 80,
    },
    squid_data: kube.PersistentVolumeClaim("proxy") {
    metadata+: { namespace: $.namespace },
    

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18. (without introducing more risk)
    A REPL for Kubernetes
    Kubeplay
    

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19. (without introducing more risk)
    errordeveloper/kubeplay
    

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20. (without introducing more risk)
    Gareth Rushgrove
    A REPL for Kubernetes
    $ ./kubeplay
    kubeplay (namespace="*")> pods # list pods in the cluster
    
    kubeplay (namespace="*")> @pod = _.any # pick a random pod from the list
    kubeplay (namespace="*")> puts @pod.to_json # output the pod definition
    {
    "metadata": {
    ...
    },
    "spec": {
    ...
    "containers": [
    {
    

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21. (without introducing more risk)
    Gareth Rushgrove
    Ruby based DSL
    @metadata = replicasets("*/").to_ruby.items.map do |k,v|
    v.metadata
    end
    @metadata.each do |i|
    puts "Name:\t#{i.name}"
    puts "Labels:\t#{i.labels}"
    puts
    end
    

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22. (without introducing more risk)
    Declarative Domain Specific Language
    Puppet
    

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23. (without introducing more risk)
    garethr/garethr-kubernetes
    

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24. (without introducing more risk)
    Gareth Rushgrove
    Puppet DSL
    kubernetes_pod { 'sample-pod':
    ensure => present,
    metadata => {
    namespace => 'default',
    },
    spec => {
    containers => [{
    name => 'container-name',
    image => 'nginx',
    }]
    },
    }
    

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25. (without introducing more risk)
    More Domain Specific Language
    Terraform
    

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26. (without introducing more risk)
    maxmanuylov/terraform-provider-kubernetes
    

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27. (without introducing more risk)
    Gareth Rushgrove
    Terraform provider
    resource "kubernetes_resource" "mypod" {
    # Required, must link on the corresponding "kubernetes_cluster" data s
    cluster = "${data.kubernetes_cluster.main.cluster}"
    collection = "pods"
    name = "mypod"
    labels {
    a = "b"
    }
    }
    

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28. (without introducing more risk)
    A compiled typed JVM language for config
    Kotlin DSL
    

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29. (without introducing more risk)
    k8-kotlin-dsl
    

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30. (without introducing more risk)
    Gareth Rushgrove
    Ingress in Kotlin
    import com.fkorotkov.kubernetes.*
    import io.fabric8.kubernetes.api.model.IntOrString
    import io.fabric8.kubernetes.client.DefaultKubernetesClient
    fun main(args: Array) {
    val client = DefaultKubernetesClient().inNamespace("default")
    client.extensions().ingresses().createOrReplace(
    ingress {
    metadata {
    name = "example-ingress"
    }
    spec {
    backend {
    

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31. (without introducing more risk)
    A scala language for kubernetes config
    Skuber
    

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32. (without introducing more risk)
    Skuber
    

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33. (without introducing more risk)
    Gareth Rushgrove
    RC in Scala
    import skuber._
    import skuber.json.format._
    val nginxSelector = Map("app" -> "nginx")
    val nginxContainer = Container("nginx",image="nginx").exposePort(80)
    val nginxController=
    ReplicationController("nginx",nginxContainer,nginxSelector)
    .withReplicas(5)
    val nginxService = Service("nginx")
    .withSelector(nginxSelector)
    .exposeOnNodePort(30001 -> 80)
    import scala.concurrent.ExecutionContext.Implicits.global
    

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34. (without introducing more risk)
    Useful parts of potential solutions
    Notable mentions
    

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35. (without introducing more risk)
    JSON Schema
    

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36. (without introducing more risk)
    Open API/Swagger
    

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37. (without introducing more risk)
    Discussion
    And thanks for listening
    

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