The scaler trait statically modifies the number of replicas of a given component. This is specilly useful for component definitions that do not provide such capability on its properties. For a dynamic approach to change the replication, check the cpuscaler trait.
The following snippet shows an application in which the number of replicas for a component is set with the trait.
apiVersion: core.oam.dev/v1beta1 kind: Application metadata: name: my-app annotations: version: "v0.0.1" description: "My scaler application" spec: components: - name: scaler-component type: worker properties: image: my-app-image:v1.0.0 cmd: ["cmd"] cpu: "0.25" memory: "200Mi" traits: - type: scaler # Set to scaler properties: replicas: 2 # (Required) number of replicas. 1 by default