kubevela.github.io/docs/platform-engineers/kube/component.md

title
How-to

In this section, it will introduce how to use simple template to declare Kubernetes API resource into a component.

Before reading this part, please make sure you've learned the definition and template concepts.

Declare ComponentDefinition

Here is a simple template based ComponentDefinition example which provides a abstraction for worker workload type:

apiVersion: core.oam.dev/v1beta1
kind: ComponentDefinition
metadata:
  name: kube-worker
  namespace: default
spec:
  workload: 
    definition: 
      apiVersion: apps/v1
      kind: Deployment
  schematic:
    kube: 
      template:
        apiVersion: apps/v1
        kind: Deployment
        spec:
          selector:
            matchLabels:
              app: nginx
          template:
            metadata:
              labels:
                app: nginx
            spec:
              containers:
              - name: nginx
                ports:
                - containerPort: 80 
      parameters: 
      - name: image
        required: true
        type: string
        fieldPaths: 
        - "spec.template.spec.containers[0].image"

In detail, the .spec.schematic.kube contains template of a workload resource and configurable parameters.

• .spec.schematic.kube.template is the simple template in YAML format.
• .spec.schematic.kube.parameters contains a set of configurable parameters. The name, type, and fieldPaths are required fields, description and required are optional fields.
  • The parameter name must be unique in a ComponentDefinition.
  • type indicates the data type of value set to the field. This is a required field which will help KubeVela to generate a OpenAPI JSON schema for the parameters automatically. In simple template, only basic data types are allowed, including string, number, and boolean, while array and object are not.
  • fieldPaths in the parameter specifies an array of fields within the template that will be overwritten by the value of this parameter. Fields are specified as JSON field paths without a leading dot, for example spec.replicas, spec.containers[0].image.

Declare an Application

Here is an example Application.

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
  name: myapp
  namespace: default
spec:
  components:
    - name: mycomp
      type: kube-worker
      properties: 
        image: nginx:1.14.0

Since parameters only support basic data type, values in properties should be simple key-value, <parameterName>: <parameterValue>.

Deploy the Application and verify the running workload instance.

kubectl get deploy

NAME                     READY   UP-TO-DATE   AVAILABLE   AGE
mycomp                   1/1     1            1           66m

And check the parameter works.

kubectl get deployment mycomp -o json | jq '.spec.template.spec.containers[0].image'

"nginx:1.14.0"