kubevela.github.io/versioned_docs/version-v0.3.5/platform-builder-guide/using-helm/trait.md

title
Attach Traits

Attach Traits to Helm Based Components

Most traits in KubeVela can be attached to Helm based component seamlessly. In this sample application below, we add two traits, scaler and virtualgroup, to a Helm based component.

apiVersion: core.oam.dev/v1alpha2
kind: Application
metadata:
  name: myapp
  namespace: default
spec:
  components:
    - name: demo-podinfo 
      type: webapp-chart 
      settings: 
        image:
          tag: "5.1.2"
      traits:
        - name: scaler
          properties:
            replicas: 4
        - name: virtualgroup
          properties:
            group: "my-group1"
            type: "cluster"

Note: when use Trait system with Helm module workload, please make sure the target workload in your Helm chart strictly follows the qualified-full-name convention in Helm. For example in this chart, the workload name is composed of release name and chart name.

This is because KubeVela relies on the name to discovery the workload, otherwise it cannot apply traits to the workload. KubeVela will generate a release name based on your Application name and component name automatically, so you need to make sure never override the full name template in your Helm chart.

Verify traits work correctly

You may wait a bit more time to check the trait works after deploying the application. Because KubeVela may not discovery the target workload immediately when it's created because of reconciliation interval.

Check the scaler trait.

$ kubectl get manualscalertrait
NAME                            AGE
demo-podinfo-scaler-d8f78c6fc   13m

$ kubectl get deployment myapp-demo-podinfo -o json | jq .spec.replicas
4

Check the virtualgroup trait.

$ kubectl get deployment myapp-demo-podinfo -o json | jq .spec.template.metadata.labels
{
  "app.cluster.virtual.group": "my-group1",
  "app.kubernetes.io/name": "myapp-demo-podinfo"
}

Update an application

After the application is deployed and workloads/traits are created successfully, you can update the application, and corresponding changes will be applied to the workload.

Let's make several changes on the configuration of the sample application.

apiVersion: core.oam.dev/v1alpha2
kind: Application
metadata:
  name: myapp
  namespace: default
spec:
  components:
    - name: demo-podinfo 
      type: webapp-chart 
      settings: 
        image:
          tag: "5.1.3" # 5.1.2 => 5.1.3 
      traits:
        - name: scaler
          properties:
            replicas: 2 # 4 => 2
        - name: virtualgroup
          properties:
            group: "my-group2" # my-group1 => my-group2
            type: "cluster"

Apply the new configuration and check the results after several minutes.

Check the new values(image.tag = 5.1.3) from application's settings are assigned to the chart.

$ kubectl get deployment myapp-demo-podinfo -o json | jq '.spec.template.spec.containers[0].image'
"ghcr.io/stefanprodan/podinfo:5.1.3"

Under the hood, Helm makes an upgrade to the release (revision 1 => 2).

$ helm ls -A
NAME              	NAMESPACE	REVISION	UPDATED                                	STATUS  	CHART        	APP VERSION
myapp-demo-podinfo	default  	2       	2021-03-15 08:52:00.037690148 +0000 UTC	deployed	podinfo-5.1.4	5.1.4

Check the scaler trait.

$ kubectl get deployment myapp-demo-podinfo -o json | jq .spec.replicas
2

Check the virtualgroup trait.

$ kubectl get deployment myapp-demo-podinfo -o json | jq .spec.template.metadata.labels
{
  "app.cluster.virtual.group": "my-group2",
  "app.kubernetes.io/name": "myapp-demo-podinfo"
}

Delete a trait

Let's have a try removing a trait from the application.

apiVersion: core.oam.dev/v1alpha2
kind: Application
metadata:
  name: myapp
  namespace: default
spec:
  components:
    - name: demo-podinfo 
      type: webapp-chart 
      settings: 
        image:
          tag: "5.1.3"
      traits:
        # - name: scaler
        #   properties:
        #    replicas: 2 
        - name: virtualgroup
          properties:
            group: "my-group2"
            type: "cluster"

Apply the configuration and check manualscalertrait has been deleted.

$ kubectl get manualscalertrait
No resources found