56 lines
2.5 KiB
Markdown
56 lines
2.5 KiB
Markdown
---
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title: Kubernetes API Aggregation Layer
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reviewers:
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- lavalamp
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- cheftako
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- chenopis
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content_type: concept
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weight: 20
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---
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<!-- overview -->
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The aggregation layer allows Kubernetes to be extended with additional APIs, beyond what is
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offered by the core Kubernetes APIs.
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The additional APIs can either be ready-made solutions such as a
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[metrics server](https://github.com/kubernetes-sigs/metrics-server), or APIs that you develop yourself.
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The aggregation layer is different from
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[Custom Resources](/docs/concepts/extend-kubernetes/api-extension/custom-resources/),
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which are a way to make the {{< glossary_tooltip term_id="kube-apiserver" text="kube-apiserver" >}}
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recognise new kinds of object.
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<!-- body -->
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## Aggregation layer
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The aggregation layer runs in-process with the kube-apiserver. Until an extension resource is
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registered, the aggregation layer will do nothing. To register an API, you add an _APIService_
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object, which "claims" the URL path in the Kubernetes API. At that point, the aggregation layer
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will proxy anything sent to that API path (e.g. `/apis/myextension.mycompany.io/v1/…`) to the
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registered APIService.
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The most common way to implement the APIService is to run an *extension API server* in Pod(s) that
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run in your cluster. If you're using the extension API server to manage resources in your cluster,
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the extension API server (also written as "extension-apiserver") is typically paired with one or
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more {{< glossary_tooltip text="controllers" term_id="controller" >}}. The apiserver-builder
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library provides a skeleton for both extension API servers and the associated controller(s).
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### Response latency
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Extension API servers should have low latency networking to and from the kube-apiserver.
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Discovery requests are required to round-trip from the kube-apiserver in five seconds or less.
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If your extension API server cannot achieve that latency requirement, consider making changes that
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let you meet it.
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## {{% heading "whatsnext" %}}
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* To get the aggregator working in your environment, [configure the aggregation layer](/docs/tasks/extend-kubernetes/configure-aggregation-layer/).
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* Then, [setup an extension api-server](/docs/tasks/extend-kubernetes/setup-extension-api-server/) to work with the aggregation layer.
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* Read about [APIService](/docs/reference/kubernetes-api/cluster-resources/api-service-v1/) in the API reference
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Alternatively: learn how to
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[extend the Kubernetes API using Custom Resource Definitions](/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions/).
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