CustomResourceDefinition

CustomResourceDefinition（CRD）是 v1.7 新增的无需改变代码就可以扩展 Kubernetes API 的机制，用来管理自定义对象。它实际上是 ThirdPartyResources（TPR）的升级版本，而 TPR 已经在 v1.8 中弃用。

API 版本对照表

CRD 示例

下面的例子会创建一个 /apis/stable.example.com/v1/namespaces/<namespace>/crontabs/… 的自定义 API：

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  # name must match the spec fields below, and be in the form: <plural>.<group>
  name: crontabs.stable.example.com
spec:
  # group name to use for REST API: /apis/<group>/<version>
  group: stable.example.com
  # versions to use for REST API: /apis/<group>/<version>
  versions:
  - name: v1beta1
    # Each version can be enabled/disabled by Served flag.
    served: true
    # One and only one version must be marked as the storage version.
    storage: true
  - name: v1
    served: true
    storage: false
  # either Namespaced or Cluster
  scope: Namespaced
  names:
    # plural name to be used in the URL: /apis/<group>/<version>/<plural>
    plural: crontabs
    # singular name to be used as an alias on the CLI and for display
    singular: crontab
    # kind is normally the CamelCased singular type. Your resource manifests use this.
    kind: CronTab
    # shortNames allow shorter string to match your resource on the CLI
    shortNames:
    - ct

API 创建好后，就可以创建具体的 CronTab 对象了

$ cat my-cronjob.yaml
apiVersion: "stable.example.com/v1"
kind: CronTab
metadata:
  name: my-new-cron-object
spec:
  cronSpec: "* * * * /5"
  image: my-awesome-cron-image
$ kubectl create -f my-crontab.yaml
crontab "my-new-cron-object" created
$ kubectl get crontab
NAME                 KIND
my-new-cron-object   CronTab.v1.stable.example.com
$ kubectl get crontab my-new-cron-object -o yaml
apiVersion: stable.example.com/v1
kind: CronTab
metadata:
  creationTimestamp: 2017-07-03T19:00:56Z
  name: my-new-cron-object
  namespace: default
  resourceVersion: "20630"
  selfLink: /apis/stable.example.com/v1/namespaces/default/crontabs/my-new-cron-object
  uid: 5c82083e-5fbd-11e7-a204-42010a8c0002
spec:
  cronSpec: '* * * * /5'
  image: my-awesome-cron-image

Finalizer

Finalizer 用于实现控制器的异步预删除钩子，可以通过 metadata.finalizers 来指定 Finalizer。

apiVersion: "stable.example.com/v1"
kind: CronTab
metadata:
  finalizers:
  - finalizer.stable.example.com

Finalizer 指定后，客户端删除对象的操作只会设置 metadata.deletionTimestamp 而不是直接删除。这会触发正在监听 CRD 的控制器，控制器执行一些删除前的清理操作，从列表中删除自己的 finalizer，然后再重新发起一个删除操作。此时，被删除的对象才会真正删除。

Validation

v1.8 开始新增了实验性的基于 OpenAPI v3 schema 的验证（Validation）机制，可以用来提前验证用户提交的资源是否符合规范。使用该功能需要配置 kube-apiserver 的 --feature-gates=CustomResourceValidation=true。

比如下面的 CRD 要求

• spec.cronSpec 必须是匹配正则表达式的字符串
• spec.replicas 必须是从 1 到 10 的整数

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: crontabs.stable.example.com
spec:
  group: stable.example.com
  version: v1
  scope: Namespaced
  names:
    plural: crontabs
    singular: crontab
    kind: CronTab
    shortNames:
    - ct
  validation:
   # openAPIV3Schema is the schema for validating custom objects.
    openAPIV3Schema:
      properties:
        spec:
          properties:
            cronSpec:
              type: string
              pattern: '^(\d+|\*)(/\d+)?(\s+(\d+|\*)(/\d+)?){4}$'
            replicas:
              type: integer
              minimum: 1
              maximum: 10

这样，在创建下面的 CronTab 时

apiVersion: "stable.example.com/v1"
kind: CronTab
metadata:
  name: my-new-cron-object
spec:
  cronSpec: "* * * *"
  image: my-awesome-cron-image
  replicas: 15

会报验证失败的错误：

The CronTab "my-new-cron-object" is invalid: []: Invalid value: map[string]interface {}{"apiVersion":"stable.example.com/v1", "kind":"CronTab", "metadata":map[string]interface {}{"name":"my-new-cron-object", "namespace":"default", "deletionTimestamp":interface {}(nil), "deletionGracePeriodSeconds":(*int64)(nil), "creationTimestamp":"2017-09-05T05:20:07Z", "uid":"e14d79e7-91f9-11e7-a598-f0761cb232d1", "selfLink":"","clusterName":""}, "spec":map[string]interface {}{"cronSpec":"* * * *", "image":"my-awesome-cron-image", "replicas":15}}:
validation failure list:
spec.cronSpec in body should match '^(\d+|\*)(/\d+)?(\s+(\d+|\*)(/\d+)?){4}$'
spec.replicas in body should be less than or equal to 10

Subresources

v1.10 开始 CRD 还支持 /status 和 /scale 等两个子资源（Beta），并且从 v1.11 开始默认开启。

v1.10 版本使用前需要在 kube-apiserver 开启 --feature-gates=CustomResourceSubresources=true。

# resourcedefinition.yaml
apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: crontabs.stable.example.com
spec:
  group: stable.example.com
  version: v1
  scope: Namespaced
  names:
    plural: crontabs
    singular: crontab
    kind: CronTab
    shortNames:
    - ct
  # subresources describes the subresources for custom resources.
  subresources:
    # status enables the status subresource.
    status: {}
    # scale enables the scale subresource.
    scale:
      # specReplicasPath defines the JSONPath inside of a custom resource that corresponds to Scale.Spec.Replicas.
      specReplicasPath: .spec.replicas
      # statusReplicasPath defines the JSONPath inside of a custom resource that corresponds to Scale.Status.Replicas.
      statusReplicasPath: .status.replicas
      # labelSelectorPath defines the JSONPath inside of a custom resource that corresponds to Scale.Status.Selector.
      labelSelectorPath: .status.labelSelector

$ kubectl create -f resourcedefinition.yaml
$ kubectl create -f- <<EOF
apiVersion: "stable.example.com/v1"
kind: CronTab
metadata:
  name: my-new-cron-object
spec:
  cronSpec: "* * * * */5"
  image: my-awesome-cron-image
  replicas: 3
EOF
$ kubectl scale --replicas=5 crontabs/my-new-cron-object
crontabs "my-new-cron-object" scaled
$ kubectl get crontabs my-new-cron-object -o jsonpath='{.spec.replicas}'
5

Categories

Categories 用来将 CRD 对象分组，这样就可以使用 kubectl get <category-name> 来查询属于该组的所有对象。

# resourcedefinition.yaml
apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: crontabs.stable.example.com
spec:
  group: stable.example.com
  version: v1
  scope: Namespaced
  names:
    plural: crontabs
    singular: crontab
    kind: CronTab
    shortNames:
    - ct
    # categories is a list of grouped resources the custom resource belongs to.
    categories:
    - all

# my-crontab.yaml
apiVersion: "stable.example.com/v1"
kind: CronTab
metadata:
  name: my-new-cron-object
spec:
  cronSpec: "* * * * */5"
  image: my-awesome-cron-image

$ kubectl create -f resourcedefinition.yaml
$ kubectl create -f my-crontab.yaml
$ kubectl get all
NAME                          AGE
crontabs/my-new-cron-object   3s

CRD 控制器

在使用 CRD 扩展 Kubernetes API 时，通常还需要实现一个新建资源的控制器，监听新资源的变化情况，并作进一步的处理。

https://github.com/kubernetes/sample-controller 提供了一个 CRD 控制器的示例，包括

• 如何注册资源 Foo
• 如何创建、删除和查询 Foo 对象
• 如何监听 Foo 资源对象的变化情况

Kubebuilder

从上面的实例中可以看到从头构建一个 CRD 控制器并不容易，需要对 Kubernetes 的 API 有深入了解，并且RBAC 集成、镜像构建、持续集成和部署等都需要很大工作量。

kubebuilder 正是为解决这个问题而生，为 CRD 控制器提供了一个简单易用的框架，并可直接生成镜像构建、持续集成、持续部署等所需的资源文件。

安装

# Install kubebuilder
VERSION=1.0.1
wget https://github.com/kubernetes-sigs/kubebuilder/releases/download/v${VERSION}/kubebuilder_${VERSION}_linux_amd64.tar.gz
tar zxvf kubebuilder_${VERSION}_linux_amd64.tar.gz
sudo mv kubebuilder_${VERSION}_linux_amd64 /usr/local/kubebuilder
export PATH=$PATH:/usr/local/kubebuilder/bin
# Install dep kustomize
go get -u github.com/golang/dep/cmd/dep
go get github.com/kubernetes-sigs/kustomize

使用方法

初始化项目

mkdir -p $GOPATH/src/demo
cd $GOPATH/src/demo
kubebuilder init --domain k8s.io --license apache2 --owner "The Kubernetes Authors"

创建 API

kubebuilder create api --group ships --version v1beta1 --kind Sloop

然后按照实际需要修改 pkg/apis/ship/v1beta1/sloop_types.go 和 pkg/controller/sloop/sloop_controller.go 增加业务逻辑。

本地运行测试

make install
make run

如果碰到错误 ValidationError(CustomResourceDefinition.status): missing required field "storedVersions" in io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1beta1.CustomResourceDefinitionStatus]，可以手动修改 config/crds/ships_v1beta1_sloop.yaml:

```yaml status: acceptedNames: kind: “” plural: “” conditions: [] storedVersions: []

然后运行 kubectl apply -f config/crds 创建 CRD。

然后就可以用 `ships.k8s.io/v1beta1` 来创建 Kind 为 `Sloop` 的资源了，比如
```sh
kubectl apply -f config/samples/ships_v1beta1_sloop.yaml

构建镜像并部署控制器

# 替换 IMG 为你自己的
export IMG=feisky/demo-crd:v1
make docker-build
make docker-push
make deploy

kustomize 已经不再支持通配符，因而上述 make deploy 可能会碰到 Load from path ../rbac/*.yaml failed 错误，解决方法是手动修改 config/default/kustomization.yaml:

resources:

• ../rbac/rbac_role.yaml
• ../rbac/rbac_role_binding.yaml
• ../manager/manager.yaml

然后执行 kustomize build config/default | kubectl apply -f - 部署，默认部署到 demo-system namespace 中。

文档和测试

# run unit tests
make test
# generate docs
kubebuilder docs

参考文档

• Extend the Kubernetes API with CustomResourceDefinitions
• CustomResourceDefinition API