第19章 Extending the Kubernetes API with Custom Resources

To create a CRD, open a YAML file and enter the fields in the following example.

apiVersion: apiextensions.k8s.io/v1beta1 1
kind: CustomResourceDefinition
metadata:
  name: crontabs.stable.example.com 2
spec:
  group: stable.example.com 3
  version: v1 4
  scope: Namespaced 5
  names:
    plural: crontabs 6
    singular: crontab 7
    kind: CronTab 8
    shortNames:
    - ct 9

After configuring the definition file, create the object:

oc create -f <file-name>.yaml

新規の RESTful API エンドポイントは以下のように作成されます。

/apis/<spec:group>/<spec:version>/<scope>/*/<names-plural>/...

For example, using the example file, the following endpoint would be created:

/apis/stable.example.com/v1/namespaces/*/crontabs/...

This endpoint URL can then be used to create and manage custom objects. The kind of object is based on the spec.kind field of the Custom Resource Definition object you created.

After the custom resource definition object has been created, you can create custom objects.

Custom objects can contain custom fields. These fields can contain arbitrary JSON.

In the following example, the cronSpec and image custom fields are set in a custom object of kind CronTab. The kind CronTab comes from the spec.kind field of the custom resource definition object you created above.

apiVersion: "stable.example.com/v1" 1
kind: CronTab 2
metadata:
  name: my-new-cron-object 3
spec: 4
  cronSpec: "* * * * /5"
  image: my-awesome-cron-image

After configuring the object file, create the object:

oc create -f <file-name>.yaml

You can then manage your custom resources.

特定の種類のカスタムリソースについての情報を取得するには、以下を入力します。

oc get <kind>

例:

oc get crontab

NAME                 KIND
my-new-cron-object   CronTab.v1.stable.example.com

リソース名では大文字と小文字が区別されず、CRD で定義される単数形または複数形のいずれか、および任意の短縮名を指定できることに注意してください。以下は例になります。

oc get crontabs
oc get crontab
oc get ct

You can also view the raw JSON data:

oc get <kind> -o yaml

You should see that it contains the custom <1> cronSpec and <2> image fields from the YAML you used to create it:

oc get ct -o yaml

apiVersion: v1
items:
- apiVersion: stable.example.com/v1
  kind: CronTab
  metadata:
    clusterName: ""
    creationTimestamp: 2017-05-31T12:56:35Z
    deletionGracePeriodSeconds: null
    deletionTimestamp: null
    name: my-new-cron-object
    namespace: default
    resourceVersion: "285"
    selfLink: /apis/stable.example.com/v1/namespaces/default/crontabs/my-new-cron-object
    uid: 9423255b-4600-11e7-af6a-28d2447dc82b
  spec:
    cronSpec: '* * * * /5' 1
    image: my-awesome-cron-image 2

Custom objects support finalizers, which allow controllers to implement conditions that must be completed before the object can be deleted.

You can add a finalizer to a custom object like this:

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

The first delete request on an object with finalizers sets a value for the metadata.deletionTimestamp field instead of deleting the object. This triggers controllers watching the object to execute any finalizers they handle.

Each controller then removes the finalizer from the list and issues the delete request again. This request deletes the object only if the list of finalizers is empty, meaning all finalizers are done.