# Customize Hook

If the customize hook is defined, Metacontroller will ask for which related objects, or classes of objects that your sync and finalize hooks need to know about. This is useful for mapping across many objects. One example would be a controller that lets you specify ConfigMaps to be placed in every Namespace. Another use-case is being able to reference other objects, e.g. the env section from a core Pod object. If you don't define a customize hook, then the related section of the hooks will be empty.

The customize hook will not provide any information about the current state of the cluster. Thus, the set of related objects may only depend on the state of the parent object.

This hook may also accept other fields in future, for other customizations.

## Customize Hook Request

A separate request will be sent for each parent object, so your hook only needs to think about one parent at a time.

The body of the request (a POST in the case of a webhook) will be a JSON object with the following fields:

FieldDescription
controllerThe whole CompositeController object, like what you might get from kubectl get compositecontroller <name> -o json.
parentThe parent object, like what you might get from kubectl get <parent-resource> <parent-name> -o json.

## Customize Hook Response

The body of your response should be a JSON object with the following fields:

FieldDescription
relatedResourcesA list of JSON objects (ResourceRules) representing all the desired related resource descriptions ().

The relatedResources field should contain a flat list of objects, not an associative array.

Each ResourceRule object should be a JSON object with the following fields:

FieldDescription
apiVersionThe API <group>/<version> of the parent resource, or just <version> for core APIs. (e.g. v1, apps/v1, batch/v1)
resourceThe canonical, lowercase, plural name of the parent resource. (e.g. deployments, replicasets, statefulsets)
labelSelectorA v1.LabelSelector object. Omit if not used (i.e. Namespace or Names should be used)
namespaceOptional. The Namespace to select in
namesOptional. A list of strings, representing individual objects to return

Important note Please note that you can specify label selector or Namespace/Names, not both in the same ResourceRule.

If the parent resource is cluster scoped and the related resource is namespaced, the namespace may be used to restrict which objects to look at. If the parent resource is namespaced, the related resources must come from the same namespace. Specifying the namespace is optional, but if specified must match.

Note that your webhook handler must return a response with a status code of 200 to be considered successful. Metacontroller will wait for a response for up to the amount defined in the Webhook spec.

## Example

Let's take a look at Global Config Map example custom resource object:

---
apiVersion: examples.metacontroller.io/v1alpha1
kind: GlobalConfigMap
name: globalsettings
spec:
sourceName: globalsettings
sourceNamespace: global


it tells that we would like to have globalsettings ConfigMap from global namespace present in each namespace.

The customize hook request will looks like :

{
'controller': '...',
'parent': '...'
}


and we need to extract information identyfying source ConfigMap.

Controller returns :

[
{
'apiVersion': 'v1',
'resource': 'configmaps',
'namespace': ${parent['spec']['sourceNamespace']}, 'names': [${parent['spec']['sourceName']}]
}, {
'apiVersion': 'v1',
'resource': 'namespaces',
'labelSelector': {}
}
]


The first RelatedRule describes that given configmap should be returned (it will be used as souce for our propagation).

The second RelatedRule describes that we want to recieve also all namespaces in the cluster ('labelSelector': {} means - select all objects).

With those rules, call to the sync hook will have non empty related field (if resources exists in the cluster), in which all objects matching given criteria will be present.