Workflow Scaling and Disruption Protection

This document describes the different alternatives for scaling a workflow and how to configure horizontal pod autoscaling and pod disruption budgets.

Scaling a Workflow

The SonataFlow CRD exposes the Kubernetes scale subresource, which enables users and controllers (such as Horizontal Pod Autoscalers) to scale workflows using the standard Kubernetes API.

Below you can see different options for scaling an example-workflow workflow.

Example workflow

apiVersion: sonataflow.org/v1alpha08
kind: SonataFlow
metadata:
  name: example-workflow
  namespace: example-workflow-namespace
  annotations:
    sonataflow.org/description: Example Workflow
    sonataflow.org/version: 0.0.1
    sonataflow.org/profile: preview
spec:
  flow:
    # Only a fragment of the workflow is shown for simplicity
    start: ExampleStartState

Workflows deployed with the dev profile are intended for development purposes and are not designed to be scaled.

Querying the workflow scale subresource

To query the workflow scale subresource you can use the following command:

kubectl get --subresource=scale example-workflow -n example-workflow-namespace -o yaml

You must get an output similar to the following:

apiVersion: autoscaling/v1
kind: Scale
metadata:
  creationTimestamp: "2026-02-12T12:48:46Z"
  name: example-workflow
  namespace: example-workflow-namespace
  resourceVersion: "38397"
  uid: de53b549-dcb5-4b46-bb4e-9a576341e099
spec:
  replicas: 1 (1)
status:
  replicas: 1 (2)
  selector: app=example-workflow,app.kubernetes.io/component=serverless-workflow,app.kubernetes.io/instance=example-workflow,app.kubernetes.io/managed-by=sonataflow-operator,app.kubernetes.io/name=example-workflow,app.kubernetes.io/version=main,sonataflow.org/workflow-app=example-workflow,sonataflow.org/workflow-namespace=example-workflow-namespace (3)

1	Number of configured replicas.
2	Number of currently available replicas.
3	Selector to query the observed Pods.

Scaling the workflow

To scale the workflow you can use any of the following alternatives:

Example of workflow scaling using the kubectl scale command

kubectl scale workflow example-workflow -n example-workflow-namespace --replicas=3

You must get an output similar to the following:

sonataflow.sonataflow.org/example-workflow scaled

Example of workflow scaling by configuring the SonataFlow CR

apiVersion: sonataflow.org/v1alpha08
kind: SonataFlow
metadata:
  name: example-workflow
  namespace: example-workflow-namespace
  annotations:
    sonataflow.org/description: Example Workflow
    sonataflow.org/version: 0.0.1
    sonataflow.org/profile: preview
spec:
  podTemplate:
    replicas: 3 (1)
  flow:
    # Only a fragment of the workflow is shown for simplicity
    start: ExampleStartState

1	Use the field `spec.podTemplate.replicas` to configure the number of replicas.

kubectl apply -f example-workflow.yaml -n example-workflow-namespace

You must get an output similar to the following:

sonataflow.sonataflow.org/example-workflow configured

Example of workflow scaling by patching the field spec.podTemplate.replicas

kubectl patch workflow example-workflow -n example-workflow-namespace \
  --type merge \
  -p '{
    "spec": {
      "podTemplate": {
        "replicas": 3
      }
    }
  }'

You must get an output similar to the following:

sonataflow.sonataflow.org/example-workflow patched

Horizontal Pod Autoscaling configuration

Before configuring a HorizontalPodAutoscaler for a workflow, ensure that the resources you want the scaler to use as metrics are defined in the SonataFlow CR.

The following example shows how to configure such resources:

Example of resources configuration in the SonataFlow CR

apiVersion: sonataflow.org/v1alpha08
kind: SonataFlow
metadata:
  name: example-workflow
  namespace: example-workflow-namespace
  annotations:
    sonataflow.org/description: Example Workflow
    sonataflow.org/version: 0.0.1
    sonataflow.org/profile: preview
spec:
  podTemplate:
    container: (1)
      resources:
        requests:
          cpu: 100m (2)
          memory: 256Mi (3)
        limits:
          cpu: 500m
          memory: 512Mi

  flow:
    # Only a fragment of the workflow is shown for simplicity
    start: ExampleStartState

1	The field `spec.podTemplate.container` supports most of the standard `PodSpec` configurations. For more information see.
2	Example of `cpu` request resource configuration.
3	Example of `memory` request resource configuration.

HorizontalPodAutoscalers use the request resources for the metrics calculations. The resource limits in the example are only illustrative and are not used for scaling.

The following example shows how to configure a HorizontalPodAutoscaler:

Example of HorizontalPodAutoscaler configuration

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: example-autoscaler
spec:
  scaleTargetRef: (1)
    apiVersion: sonataflow.org/v1alpha08
    kind: SonataFlow
    name: example-workflow
  minReplicas: 3
  maxReplicas: 10
  metrics:
    - type: Resource
      resource:
        name: cpu (2)
        target:
          type: Utilization
          averageUtilization: 70

1	Refer the target workflow by configuring the `apiVersion`, `kind` and `name`.
2	Example of a metric based on the cpu resource utilization.

Workflows deployed with spec.podTemplate.deploymentModel: knative cannot be scaled via a HorizontalPodAutoscaler, since Knative Serving controls the number of replicas automatically.

For more information on configuring HorizonalPodAutoscalers you can refer to the Kubernetes documentation

Additional resources

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