Override Policy

The OverridePolicy and ClusterOverridePolicy are used to declare override rules for resources when they are propagating to different clusters.

Difference between OverridePolicy and ClusterOverridePolicy

ClusterOverridePolicy represents the cluster-wide policy that overrides a group of resources to one or more clusters while OverridePolicy will apply to resources in the same namespace as the namespace-wide policy. For cluster scoped resources, apply ClusterOverridePolicy by policies name in ascending. For namespaced scoped resources, first apply ClusterOverridePolicy, then apply OverridePolicy.

Resource Selector

ResourceSelectors restricts resource types that this override policy applies to. If you ignore this field it means matching all resources.

Resource Selector required apiVersion field which represents the API version of the target resources and kind which represents the Kind of the target resources. The allowed selectors are as follows:

• namespace: namespace of the target resource.
• name: name of the target resource
• labelSelector: A label query over a set of resources.

Examples

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  resourceSelectors:
    - apiVersion: apps/v1
      kind: Deployment
      name: nginx
      namespace: test
      labelSelector:
        matchLabels:
          app: nginx
  overrideRules:
  ...

It means override rules above will only be applied to Deployment which is named nginx in test namespace and has labels with app: nginx.

Target Cluster

Target Cluster defines restrictions on the override policy that only applies to resources propagated to the matching clusters. If you ignore this field it means matching all clusters.

The allowed selectors are as follows:

• labelSelector: a filter to select member clusters by labels.
• fieldSelector: a filter to select member clusters by fields. Currently only three fields of provider(cluster.spec.provider), zone(cluster.spec.zone), and region(cluster.spec.region) are supported.
• clusterNames: the list of clusters to be selected.
• exclude: the list of clusters to be ignored.

labelSelector

Examples

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  ...
  overrideRules:
    - targetCluster:
        labelSelector:
          matchLabels:
            cluster: member1 
      overriders:
      ...

It means override rules above will only be applied to those resources propagated to clusters which has cluster: member1 label.

fieldSelector

Examples

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  ...
  overrideRules:
    - targetCluster:
        fieldSelector:
          matchExpressions:
            - key: region
              operator: In
              values:
                - cn-north-1
      overriders:
      ...

It means override rules above will only be applied to those resources propagated to clusters which has the spec.region field with values in [cn-north-1].

clusterNames

Examples

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  ...
  overrideRules:
    - targetCluster:
        clusterNames:
          - member1
      overriders:
      ...

It means override rules above will only be applied to those resources propagated to clusters whose clusterNames are member1.

exclude

Examples

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  ...
  overrideRules:
    - targetCluster:
        exclude:
          - member1
      overriders:
      ...

It means override rules above will only be applied to those resources propagated to clusters whose clusterNames are not member1.

Overriders

Karmada offers various alternatives to declare the override rules:

• ImageOverrider: dedicated to override images for workloads.
• CommandOverrider: dedicated to override commands for workloads.
• ArgsOverrider: dedicated to override args for workloads.
• PlaintextOverrider: a general-purpose tool to override any kind of resources.

ImageOverrider

The ImageOverrider is a refined tool to override images with format [registry/]repository[:tag|@digest](e.g./spec/template/spec/containers/0/image) for workloads such as Deployment.

The allowed operations are as follows:

• add: appends the registry, repository or tag/digest to the image from containers.
• remove: removes the registry, repository or tag/digest from the image from containers.
• replace: replaces the registry, repository or tag/digest of the image from containers.

Examples

Suppose we create a deployment named myapp.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
  ...
spec:
  template:
    spec:
      containers:
        - image: myapp:1.0.0
          name: myapp

Example 1: Add the registry when workloads are propagating to specific clusters.

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  ...
  overrideRules:
    - overriders:
        imageOverrider:
          - component: Registry
            operator: add
            value: test-repo

It means add a registrytest-repo to the image of myapp.

After the policy is applied for myapp, the image will be:

      containers:
        - image: test-repo/myapp:1.0.0
          name: myapp

Example 2: replace the repository when workloads are propagating to specific clusters.

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  ...
  overrideRules:
    - overriders:
        imageOverrider:
          - component: Repository
            operator: replace
            value: myapp2

It means replace the repository from myapp to myapp2.

After the policy is applied for myapp, the image will be:

      containers:
        - image: myapp2:1.0.0
          name: myapp

Example 3: remove the tag when workloads are propagating to specific clusters.

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  ...
  overrideRules:
    - overriders:
        imageOverrider:
          - component: Tag
            operator: remove

It means remove the tag of the image myapp.

After the policy is applied for myapp, the image will be:

      containers:
        - image: myapp
          name: myapp

CommandOverrider

The CommandOverrider is a refined tool to override commands(e.g./spec/template/spec/containers/0/command) for workloads, such as Deployment.

The allowed operations are as follows:

• add: appends one or more flags to the command list.
• remove: removes one or more flags from the command list.

Examples

Suppose we create a deployment named myapp.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
  ...
spec:
  template:
    spec:
      containers:
        - image: myapp
          name: myapp
          command:
            - ./myapp
            - --parameter1=foo
            - --parameter2=bar

Example 1: Add flags when workloads are propagating to specific clusters.

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  ...
  overrideRules:
    - overriders:
        commandOverrider:
          - containerName: myapp
            operator: add
            value:
              - --cluster=member1

It means add(appending) a new flag --cluster=member1 to the myapp.

After the policy is applied for myapp, the command list will be:

      containers:
        - image: myapp
          name: myapp
          command:
            - ./myapp
            - --parameter1=foo
            - --parameter2=bar
            - --cluster=member1

Example 2: Remove flags when workloads are propagating to specific clusters.

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  ...
  overrideRules:
    - overriders:
        commandOverrider:
          - containerName: myapp
            operator: remove
            value:
              - --parameter1=foo

It means remove the flag --parameter1=foo from the command list.

After the policy is applied for myapp, the command will be:

      containers:
        - image: myapp
          name: myapp
          command:
            - ./myapp
            - --parameter2=bar

ArgsOverrider

The ArgsOverrider is a refined tool to override args(such as /spec/template/spec/containers/0/args) for workloads, such as Deployments.

The allowed operations are as follows:

• add: appends one or more args to the command list.
• remove: removes one or more args from the command list.

Note: the usage of ArgsOverrider is similar to CommandOverrider, You can refer to the CommandOverrider examples.

PlaintextOverrider

The PlaintextOverrider is a simple overrider that overrides target fields according to path, operator and value, just like kubectl patch.

The allowed operations are as follows:

• add: appends one or more elements to the resources.
• remove: removes one or more elements from the resources.
• replace: replaces one or more elements from the resources.

Suppose we create a configmap named myconfigmap.

apiVersion: v1
kind: ConfigMap
metadata:
  name: myconfigmap
  ...
data:
  example: 1

Example 1: replace data of the configmap when resources are propagating to specific clusters.

apiVersion: policy.karmada.io/v1alpha1
kind: OverridePolicy
metadata:
  name: example
spec:
  ...
  overrideRules:
    - overriders:
        plaintext:
          - path: /data/example
            operator: replace
            value: 2

It means replace data of the configmap from example: 1 to the example: 2.

After the policy is applied for myconfigmap, the configmap will be:

apiVersion: v1
kind: ConfigMap
metadata:
  name: myconfigmap
  ...
data:
  example: 2