---
title: Extension API Server
---

<head>
  <link rel="canonical" href="https://ranchermanager.docs.rancher.com/api/extension-apiserver"/>
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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 Kubernetes supported in this Rancher versions K8s distributions (RKE2/K3s) will have the aggregation layer configured and enabled by default. However, if you suspect that your cluster configuration is incorrect, refer to the [Kubernetes Aggregation Layer documentation](https://kubernetes.io/docs/tasks/extend-kubernetes/configure-aggregation-layer/) for information on configuring the aggregation layer.


:::note
If the underlying Kubernetes distribution does not support the aggregation layer, you must migrate to a Kubernetes distribution that does before upgrading.
:::
