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 current stable version, which only includes support for CPU autoscaling, can
be found in the autoscaling/v1 API version. The alpha version, which includes
support for scaling on memory and custom metrics, can be found in
autoscaling/v2beta1 (and autoscaling/v2beta2 in 1.12 and later).
kOps can assist in setting up HPA. Relevant reading you will need to go through:
- Extending the Kubernetes API with the aggregation layer
- Configure The Aggregation Layer
- Horizontal Pod Autoscaling
While the above links go into details on how Kubernetes needs to be configured to work with HPA, a lot of that 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:-
--horizontal-pod-autoscaler-use-rest-clientsshould be true. -
--kubeconfig <path-to-kubeconfig>
-
To enable the resource metrics API for scaling on CPU and memory, install metrics-server (installation instruction here). The compatibility matrix is as follows:
| Metrics Server | Metrics API group/version | Supported Kubernetes version |
|---|---|---|
| 0.3.x | metrics.k8s.io/v1beta1 |
1.8+ |
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.