Technically, the Horizontal Pod Autoscaler is a controller in the Kubernetes controller manager, and it is configured by HorizontalPodAutoscaler resource objects.
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That's how the Horizontal Pod Autoscaler works, but how do you use it?
Configuring the Horizontal Pod Autoscaler to autoscale your app is done by creating a HorizontalPodAutoscaler resource.
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When you define a HorizontalPodAutoscaler resource you have to specify such a metric.
But how does the Horizontal Pod Autoscaler know how to obtain these metrics?
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The Horizontal Pod Autoscaler queries metrics from the metrics registry:
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The Horizontal Pod Autoscaler is one of these clients.
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Any metric that you want to use as a scaling metric must be exposed through one of these three metric APIs.
Because only in that way they are accessible to the Horizontal Pod Autoscaler.
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