You are viewing documentation for Kubernetes version: v1.19
Kubernetes v1.19 documentation is no longer actively maintained. The version you are currently viewing is a static snapshot. For up-to-date documentation, see the latest version.
Extending the Kubernetes API with the aggregation layer
The aggregation layer allows Kubernetes to be extended with additional APIs, beyond what is offered by the core Kubernetes APIs. The additional APIs can either be ready-made solutions such as service-catalog, or APIs that you develop yourself.
The aggregation layer is different from Custom Resources, which are a way to make the kube-apiserver recognise new kinds of object.
Aggregation layer
The aggregation layer runs in-process with the kube-apiserver. Until an extension resource is registered, the aggregation layer will do nothing. To register an API, you add an APIService object, which "claims" the URL path in the Kubernetes API. At that point, the aggregation layer will proxy anything sent to that API path (e.g. /apis/myextension.mycompany.io/v1/…) to the registered APIService.
The most common way to implement the APIService is to run an extension API server in Pod(s) that run in your cluster. If you're using the extension API server to manage resources in your cluster, the extension API server (also written as "extension-apiserver") is typically paired with one or more controllers. The apiserver-builder library provides a skeleton for both extension API servers and the associated controller(s).
Response latency
Extension API servers should have low latency networking to and from the kube-apiserver. Discovery requests are required to round-trip from the kube-apiserver in five seconds or less.
If your extension API server cannot achieve that latency requirement, consider making changes that let you meet it. You can also set the
EnableAggregatedDiscoveryTimeout=false feature gate on the kube-apiserver
to disable the timeout restriction. This deprecated feature gate will be removed in a future release.
What's next
- To get the aggregator working in your environment, configure the aggregation layer.
- Then, setup an extension api-server to work with the aggregation layer.
- Also, learn how to extend the Kubernetes API using Custom Resource Definitions.
- Read the specification for APIService