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horizontal_pod_autoscaling.md

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Horizontal Pod Autoscaling

With Horizontal Pod Autoscaling, Kubernetes automatically scales the number of pods in a replication controller, deployment, or replica set based on observed CPU utilization (or, with alpha support, on some other, application-provided metrics).

The HorizontalPodAutscaler autoscaling/v2 stable API moved to GA in 1.23. The previous stable version, which only includes support for CPU autoscaling, can be found in the autoscaling/v1 API version. The beta version, which includes support for scaling on memory and custom metrics, can be found in autoscaling/v2beta1 in 1.8 - 1.24 (and autoscaling/v2beta2 in 1.12 - 1.25).

kOps sets up HPA out of the box. Relevant reading to go through:

While the above links go into details on how Kubernetes needs to be configured to work with HPA, the work is already done for you by kOps. Specifically:

  • Enable the Aggregation Layer via the following kube-apiserver flags:
    • --requestheader-client-ca-file=<path to aggregator CA cert>
    • --requestheader-allowed-names=aggregator
    • --requestheader-extra-headers-prefix=X-Remote-Extra-
    • --requestheader-group-headers=X-Remote-Group
    • --requestheader-username-headers=X-Remote-User
    • --proxy-client-cert-file=<path to aggregator proxy cert>
    • --proxy-client-key-file=<path to aggregator proxy key>
  • Enable Horizontal Pod Scaling ... set the appropriate flags for kube-controller-manager:
    • --kubeconfig <path-to-kubeconfig>

Cluster Configuration

Support For Multiple Metrics

To enable the resource metrics API for scaling on CPU and memory, enable metrics-server by setting spec.metricsServer.enabled=true in the Cluster spec. The compatibility matrix is as follows:

Metrics Server Metrics API group/version Supported Kubernetes version
0.3.x metrics.k8s.io/v1beta1 1.8+

Support For Custom Metrics

To enable the custom metrics API, register it via the API aggregation layer. If you're using Prometheus, checkout the custom metrics adapter for Prometheus.