Restore Resource Modifiers

Resource Modifiers

Velero provides a generic ability to modify the resources during restore by specifying json patches. The json patches are applied to the resources before they are restored. The json patches are specified in a configmap and the configmap is referenced in the restore command.

Creating resource Modifiers

Below is the two-step of using resource modifiers to modify the resources during restore.

Creating resource modifiers configmap

You need to create one configmap in Velero install namespace from a YAML file that defined resource modifiers. The creating command would be like the below:
```
kubectl create cm <configmap-name> --from-file <yaml-file> -n velero
```
Creating a restore reference to the defined resource policies

You can create a restore with the flag --resource-modifier-configmap, which will apply the defined resource modifiers to the current restore. The creating command would be like the below:
```
velero restore create --resource-modifier-configmap <configmap-name>
```

YAML template

Yaml template:

version: v1
resourceModifierRules:
- conditions:
     groupResource: persistentvolumeclaims
     resourceNameRegex: "^mysql.*$"
     namespaces:
     - bar
     - foo
     labelSelector:
        matchLabels:
           foo: bar
  patches:
  - operation: replace
    path: "/spec/storageClassName"
    value: "premium"
  - operation: remove
    path: "/metadata/labels/test"

The above configmap will apply the JSON Patch to all the PVCs in the namespaces bar and foo with name starting with mysql and match label foo: bar. The JSON Patch will replace the storageClassName with “premium” and remove the label “test” from the PVCs.
Note that the Namespace here is the original namespace of the backed up resource, not the new namespace where the resource is going to be restored.
You can specify multiple JSON Patches for a particular resource. The patches will be applied in the order specified in the configmap. A subsequent patch is applied in order and if multiple patches are specified for the same path, the last patch will override the previous patches.
You can specify multiple resourceModifierRules in the configmap. The rules will be applied in the order specified in the configmap.

Operations supported by the JSON Patch RFC:

add
remove
replace
move
copy
test (covered below)

Advanced scenarios

Conditional patches using test operation

The test operation can be used to check if a particular value is present in the resource. If the value is present, the patch will be applied. If the value is not present, the patch will not be applied. This can be used to apply a patch only if a particular value is present in the resource. For example, if you wish to change the storage class of a PVC only if the PVC is using a particular storage class, you can use the following configmap.

version: v1
resourceModifierRules:
- conditions:
    groupResource: persistentvolumeclaims
    resourceNameRegex: ".*"
    namespaces:
    - bar
    - foo
  patches:
  - operation: test
    path: "/spec/storageClassName"
    value: "premium"
  - operation: replace
    path: "/spec/storageClassName"
    value: "standard"

Other examples

version: v1
resourceModifierRules:
- conditions:
    groupResource: deployments.apps
    resourceNameRegex: "^test-.*$"
    namespaces:
    - bar
    - foo
  patches:
    # Dealing with complex values by escaping the yaml
  - operation: add
    path: "/spec/template/spec/containers/0"
    value: "{\"name\": \"nginx\", \"image\": \"nginx:1.14.2\", \"ports\": [{\"containerPort\": 80}]}"
    # Copy Operator
  - operation: copy
    from: "/spec/template/spec/containers/0"
    path: "/spec/template/spec/containers/1"

Note:

The design and approach is inspired from kubectl patch command
Update a container’s image using a json patch with positional arrays kubectl patch pod valid-pod -type=‘json’ -p='[{“op”: “replace”, “path”: “/spec/containers/0/image”, “value”:“new image”}]'
Before creating the resource modifier yaml, you can try it out using kubectl patch command. The same commands should work as it is.

JSON Merge Patch

You can modify a resource using JSON Merge Patch

version: v1
resourceModifierRules:
- conditions:
    groupResource: pods
    namespaces:
    - ns1
  mergePatches:
  - patchData: |
      {
        "metadata": {
          "annotations": {
            "foo": null
          }
        }
      }

The above configmap will apply the Merge Patch to all the pods in namespace ns1 and remove the annotation foo from the pods.
Both json and yaml format are supported for the patchData.
For more details, please refer to this doc

Strategic Merge Patch

You can modify a resource using Strategic Merge Patch

version: v1
resourceModifierRules:
- conditions:
    groupResource: pods
    resourceNameRegex: "^my-pod$"
    namespaces:
    - ns1
  strategicPatches:
  - patchData: |
      {
        "spec": {
          "containers": [
            {
              "name": "nginx",
              "image": "repo2/nginx"
            }
          ]
        }
      }

The above configmap will apply the Strategic Merge Patch to the pod with name my-pod in namespace ns1 and update the image of container nginx to repo2/nginx.
Both json and yaml format are supported for the patchData.
For more details, please refer to this doc

Conditional Patches in ALL Patch Types

A new field matches is added in conditions to support conditional patches.

Example of matches in conditions

version: v1
resourceModifierRules:
- conditions:
    groupResource: persistentvolumeclaims.storage.k8s.io
    matches:
    - path: "/spec/storageClassName"
      value: "premium"
  mergePatches:
  - patchData: |
      {
        "metadata": {
          "annotations": {
            "foo": null
          }
        }
      }

The above configmap will apply the Merge Patch to all the PVCs in all namespaces with storageClassName premium and remove the annotation foo from the PVCs.
You can specify multiple rules in the matches list. The patch will be applied only if all the matches are satisfied.

Wildcard Support for GroupResource

The user can specify a wildcard for groupResource in the conditions' struct. This will allow the user to apply the patches for all the resources of a particular group or all resources in all groups. For example, *.apps will apply to all the resources in the apps group, * will apply to all the resources in core group, *.* will apply to all the resources in all groups.

If both *.groupName and namespaces are specified, the patches will be applied to all the namespaced resources in this group in the specified namespaces and all the cluster resources in this group.

Documentation