--- title: Extension API Server --- Rancher extends Kubernetes with additional APIs by registering an extension API server using the [Kubernetes API Aggregation Layer](https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/apiserver-aggregation/). ## Aggregation Layer is Required The API aggregation layer must be configured on the local Kubernetes cluster for the `v1.ext.cattle.io` `APIService` to work correctly. If the `APIService` does not receive a registration request after the Rancher server starts, the pod will crash with a log entry indicating the error. If your pods are consistently failing to detect registration despite having a correctly configured cluster, you can increase the timeout by setting the `.Values.aggregationRegistrationTimeout` in helm. All versions of k8s supported by Rancher with the feature will have the aggregation layer configured by default. If you suspect your cluster may not be configured properly, see the [Kubernetes Aggregation Layer docs](https://kubernetes.io/docs/tasks/extend-kubernetes/configure-aggregation-layer/) for information on configuring the aggregation layer. :::note If the underlying kubernetes distro does not support the aggregation layer, you must migrate to a distro that does before upgrading. :::