Policy Definition

    Generate resources in policy is similar to trait, policy can be used to define things across components.

    Let’s use to create a basic policy scaffold:

    The content of the scaffold expected to be:

    1. // $ cat myroute.cue
    2. "my-plc": {
    3.     annotations: {}
    4.     attributes: {}
    5.     description: "My ingress route policy."
    6.     labels: {}
    7.     type: "policy"
    8. }
    10. template: {
    11. }

    The rule is aligned with component definition, you must specify output, while you can use outputs for more objects, the format as below:

    1. "my-plc": {
    2.     description: "My service mesh policy."
    3.     type:        "policy"
    4. }
    6. template: {
    7.     #ServerWeight: {
    9.     }
    10.     parameter: {
    11.         weights: [...#ServerWeight]
    12.     }
    14.     output: {
    15.         apiVersion: "split.smi-spec.io/v1alpha3"
    16.         kind:       "TrafficSplit"
    17.         metadata: name: context.name
    18.         spec: {
    19.             service:  context.name
    20.             backends: parameter.weights
    21.         }
    22.     }
    23. }

    Apply to our control plane to make this Policy work:

    Then our end users can discover it immediately and use it in Application.

    After using vela up by the following command:

    1. cat <<EOF | vela up -f -
    2. apiVersion: core.oam.dev/v1beta1
    4. metadata:
    5. spec:
    6.   components:
    7.     - name: server-v1
    8.       type: webservice
    9.       properties:
    10.         image: oamdev/hello-world:v1
    11.     - name: server-v2
    12.       type: webservice
    13.       properties:
    14.         image: oamdev/hello-world:v2
    15.   policies:
    16.     - type: my-plc
    17.       name: unified
    18.       properties:
    19.         weights:
    20.           - service: server-v1
    21.             weight: 80
    22.           - service: server-v2

    The policy will generate Kubernetes resources by KubeVela like below:

    Not all policies generate resources, there’re several built-in policies which are used to control the whole delivery precess and workflows.

    tip

    These special polices are usually coded in the application controller.