One-time Delivery (Coordinate with Multi-Controllers)

By default, the KubeVela controller will prevent configuration drift for applied resources by reconciling them routinely. This is useful if you want to keep your application always having the desired configuration to avoid some unintentional changes by external modifiers.

However, sometimes, you might want to use KubeVela Application to dispatch jobs and recycle jobs, but also want to leave those resources mutable after the workflow is finished. In this case, you can use the following apply-once policy. Some use cases:

1. Working with HPA, which will change the deployment replicas.
2. Working with Istio, which will change the deployment containers.
3. Other controllers…

All managed fields once apply

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
  name: apply-once-app
spec:
  components:
    - name: hello-world
      type: webservice
      properties:
        image: oamdev/hello-world
      traits:
        - type: scaler
          properties:
            replicas: 3
  policies:
    - name: apply-once
      type: apply-once
      properties:
        enable: true

In this case, if you change the replicas or other managed fields of the hello-world deployment after the application enters the running state, the change will not be reverted. On the contrary, if you disable the apply-once policy (by default), any changes to the replicas of the hello-world application will be brought back in the next reconcile loop.

Specified fields once apply

apiVersion: core.oam.dev/v1beta1
kind: Application
metadata:
  name: apply-once-app
spec:
  components:
    - name: hello-world
      type: webservice
      properties:
        image: oamdev/hello-world
      traits:
        - type: scaler
          properties:
            replicas: 3
  policies:
    - name: apply-once
      type: apply-once
      properties:
        enable: true
        rules:
        - strategy:
            path: ["spec.replicas"]
          selector:
            resourceTypes: ["Deployment"]

In this case, only support changing the replicas field by other controllers, such as HPA. The selector rule support: componentNames,componentTypes,oamTypes,resourceNames,resourceTypes and traitTypes.

The configuration drift check will be launched every 5 minutes after the application enters the running state or the suspending state without errors. You can configure the time by setting the application-re-sync-period bootstrap parameter in the controller. See bootstrap parameters for details.