Override Policy

The OverridePolicy and ClusterOverridePolicy are used to define override rules for resources when they are being propagated 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 order. For namespaced scoped resources, ClusterOverridePolicy is applied first, followed by OverridePolicy.

Resource Selector

ResourceSelectors restrict resource types that the override policy applies to. If you ignore this field, it matches all resources.

Resource Selector requires the 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

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   resourceSelectors:
  7.     - apiVersion: apps/v1
  8.       kind: Deployment
  9.       name: nginx
  10.       namespace: test
  11.       labelSelector:
  12.         matchLabels:
  13.           app: nginx
  14.   overrideRules:
  15.   #...

Override rules above will only be applied to the Deployment named nginx in test namespace and has the app: nginx label.

Target Cluster

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

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - targetCluster:
  9.         labelSelector:
  10.           matchLabels:
  11.             cluster: member1 
  12.       overriders:
  13.       #...

Override rules above will only be applied to resources propagated to clusters which have the cluster: member1 label.

fieldSelector

Examples

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - targetCluster:
  9.         fieldSelector:
  10.           matchExpressions:
  11.             - key: region
  12.               operator: In
  13.               values:
  14.                 - cn-north-1
  15.       overriders:
  16.       #...

Override rules above will only be applied to resources propagated to clusters which have the spec.region field with values in [cn-north-1].

Examples

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - targetCluster:
  9.         fieldSelector:
  10.           matchExpressions:
  11.             - key: provider
  12.               operator: In
  13.               values:
  14.                 - aws
  15.       overriders:
  16.       #...

Override rules above will only be applied to resources propagated to clusters which have the spec.provider field with values in [aws].

Examples

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - targetCluster:
  9.         fieldSelector:
  10.           matchExpressions:
  11.             - key: zone
  12.               operator: In
  13.               values:
  14.                 - us
  15.       overriders:
  16.       #...

Override rules above will only be applied to resources propagated to clusters which have the spec.zone field with values in [us].

clusterNames

Examples

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - targetCluster:
  9.         clusterNames:
  10.           - member1
  11.       overriders:
  12.       #...

Override rules above will only be applied to resources propagated to clusters whose clusterNames are member1.

exclude

Examples

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - targetCluster:
  9.         exclude:
  10.           - member1
  11.       overriders:
  12.       #...

Override rules above will only be applied to resources propagated to clusters whose clusterNames are not member1.

Overriders

Karmada offers various alternatives to declare the override rules:

  • ImageOverrider: overrides images for workloads.
  • CommandOverrider: overrides commands for workloads.
  • ArgsOverrider: overrides args for workloads.
  • LabelsOverrider: overrides labels for workloads.
  • AnnotationsOverrider: overrides annotations for workloads.
  • PlaintextOverrider: a general-purpose tool to override any kind of resources.
  • FieldOverrider: partially override values inside JSON and YAML fields.

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.

  1. apiVersion: apps/v1
  2. kind: Deployment
  3. metadata:
  4.   name: myapp
  5.   #...
  6. spec:
  7.   template:
  8.     spec:
  9.       containers:
  10.         - image: myapp:1.0.0
  11.           name: myapp

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

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - overriders:
  9.         imageOverrider:
  10.           - component: Registry
  11.             operator: add
  12.             value: test-repo

This will add a test-repo registry to the image of myapp.

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

  1.       containers:
  2.         - image: test-repo/myapp:1.0.0
  3.           name: myapp

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

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - overriders:
  9.         imageOverrider:
  10.           - component: Repository
  11.             operator: replace
  12.             value: myapp2

This will replace the myapp repo with myapp2 on the image.

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

  1.       containers:
  2.         - image: myapp2:1.0.0
  3.           name: myapp

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

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - overriders:
  9.         imageOverrider:
  10.           - component: Tag
  11.             operator: remove

This will remove the myapp image’s tag.

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

  1.       containers:
  2.         - image: myapp
  3.           name: myapp

CommandOverrider

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

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.

  1. apiVersion: apps/v1
  2. kind: Deployment
  3. metadata:
  4.   name: myapp
  5.   #...
  6. spec:
  7.   template:
  8.     spec:
  9.       containers:
  10.         - image: myapp
  11.           name: myapp
  12.           command:
  13.             - ./myapp
  14.             - --parameter1=foo
  15.             - --parameter2=bar

Example 1: add flags when propagating workloads to specific clusters.

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - overriders:
  9.         commandOverrider:
  10.           - containerName: myapp
  11.             operator: add
  12.             value:
  13.               - --cluster=member1

This will add (append) a new flag --cluster=member1 to myapp command.

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

  1.       containers:
  2.         - image: myapp
  3.           name: myapp
  4.           command:
  5.             - ./myapp
  6.             - --parameter1=foo
  7.             - --parameter2=bar
  8.             - --cluster=member1

Example 2: remove flags when propagating workloads to specific clusters.

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - overriders:
  9.         commandOverrider:
  10.           - containerName: myapp
  11.             operator: remove
  12.             value:
  13.               - --parameter1=foo

This will remove the flag --parameter1=foo from the command list.

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

  1.       containers:
  2.         - image: myapp
  3.           name: myapp
  4.           command:
  5.             - ./myapp
  6.             - --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: ArgsOverrider functions similarly to CommandOverrider. You can refer to the CommandOverrider examples.

LabelsOverrider

The allowed operations are as follows:

  • add: the items in value will be appended to labels.
  • remove: if the item in value matches the item in labels, the former will be deleted. If they do not match, nothing will be done.
  • replace: if the key in value matches the key in the label, the former will be replaced. If they do not match, nothing will be done.

Examples

Suppose we create a deployment named myapp.

  1. apiVersion: apps/v1
  2. kind: Deployment
  3. metadata:
  4.   name: myapp
  5.   labels: 
  6.     foo: foo
  7.     baz: baz
  8.   #...
  9. spec:
  10.   template:
  11.     spec:
  12.       containers:
  13.         - image: myapp:1.0.0
  14.           name: myapp

Example 1: add/remove/replace labels

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - overriders:
  9.         labelsOverrider:
  10.           - operator: add
  11.             value: 
  12.               bar: bar  # It will be added to labels
  13.           - operator: replace
  14.             value: 
  15.               foo: exist # "foo: foo" will be replaced by "foo: exist"
  16.           - operator: remove
  17.             value: 
  18.               baz: baz   # It will be removed from labels

AnnotationsOverrider

Note: AnnotationsOverrider functions similarly to LabelsOverrider. You can refer to the LabelsOverrider examples.

FieldOverrider

The FieldOverrider allows users to partially override values inside JSON and YAML fields.

The allowed operations are as follows:

  • add: appends new key-value pairs at the specified sub path.
  • remove: removes specific key-value pairs at the specified sub path.
  • replace: replaces existing values with new values at the specified sub path.

Suppose we have a ConfigMap named myconfigmap that contains some nested YAML data:

  1. apiVersion: v1
  2. kind: ConfigMap
  3. metadata:
  4.   name: myconfigmap
  5. data:
  6.   config.yaml: |
  7.     app:
  8.       database:
  9.         port: 5432

Example 1: replace the database port within the ConfigMap using YAML Patch operations.

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - overriders:
  9.         fieldOverrider:
  10.           - fieldPath: /data/config.yaml
  11.             yaml:
  12.               - subPath: /app/database/port
  13.                 operator: replace
  14.                 value: "3306"

After applying this OverridePolicy, the ConfigMap will be updated as follows:

  1. apiVersion: v1
  2. kind: ConfigMap
  3. metadata:
  4.   name: myconfigmap
  5. data:
  6.   config.yaml: |
  7.     app:
  8.       database:
  9.         port: 3306

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.

  1. apiVersion: v1
  2. kind: ConfigMap
  3. metadata:
  4.   name: myconfigmap
  5.   #...
  6. data:
  7.   example: 1

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

  1. apiVersion: policy.karmada.io/v1alpha1
  2. kind: OverridePolicy
  3. metadata:
  4.   name: example
  5. spec:
  6.   #...
  7.   overrideRules:
  8.     - overriders:
  9.         plaintext:
  10.           - path: /data/example
  11.             operator: replace
  12.             value: 2

This will replace data of the configmap from example: 1 to example: 2.

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

  1. apiVersion: v1
  2. kind: ConfigMap
  3. metadata:
  4.   name: myconfigmap
  5.   #...
  6. data:
  7.   example: 2