Update horizontal_pod_autoscaling.md

docs/horizontal_pod_autoscaling.md

@@ -1,17 +1,16 @@
 # 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
+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/v2alpha1` in 1.7 and `autoscaling/v2beta1` 1.8 and 1.9.
+`autoscaling/v2beta1` (and `autoscaling/v2beta2` in 1.12 and later).
 
-Kops can assist in setting up HPA and recommends Kubernetes `1.7.x` to `1.9.x`
+Kops can assist in setting up HPA. Relevant reading you will need to go through:
-and Kops `>=1.7`. Relevant reading you will need to go through:
 
 * [Extending the Kubernetes API with the aggregation layer][k8s-extend-api]
 * [Configure The Aggregation Layer][k8s-aggregation-layer]
@@ -35,102 +34,25 @@ Specifically:
    * [x] `--horizontal-pod-autoscaler-use-rest-clients` should be true.
    * [x] `--kubeconfig <path-to-kubeconfig>`
 
-Ensure that you use **1.8.5 at minimum for Kubernetes 1.8.x** due to [a nasty
-bug affecting the API aggregation layer][issue-1]. It was fixed in
-[kubernetes/kubernetes#55259][pr-5].
-
 ## Cluster Configuration
 
 ### Support For Multiple Metrics
 
-Enable API versions required to support scaling on cpu, memory and custom
+To enable the resource metrics API for scaling on CPU and memory, install metrics-server
-metrics:
+([installation instruction here][k8s-metrics-server]). The
-
-```yaml
-# On K8s 1.7
-spec:
-  kubeAPIServer:
-    runtimeConfig:
-      autoscaling/v2alpha1: "true"
-```
-
-```yaml
-# On K8s 1.8 and 1.9
-spec:
-  kubeAPIServer:
-    runtimeConfig:
-      autoscaling/v2beta1: "true"
-```
-
-If you've set the above configuration, your cluster is now ready for the
-resource metrics API ([installation instruction here][k8s-metrics-server]). The
 compatibility matrix is as follows:
 
 Metrics Server | Metrics API group/version | Supported Kubernetes version
 ---------------|---------------------------|-----------------------------
 0.3.x          | `metrics.k8s.io/v1beta1`  | 1.8+
-0.2.x          | `metrics.k8s.io/v1beta1`  | 1.8+
-0.1.x          | `metrics/v1alpha1`        | 1.7
 
 ### Support For Custom Metrics
 
-Enable gathering custom metrics:
+To enable the custom metrics API, register it via the API aggregation layer. If you're using
-
-```yaml
-spec:
-  kubelet:
-    enableCustomMetrics: true
-```
-
-Note that the deprecated and inactive option '--enable-custom-metrics' has been removed in Kubernetes 1.11 [#60699](https://github.com/kubernetes/kubernetes/pull/60699)
-
-Enable the horizontal pod autoscaler REST client:
-
-```yaml
-spec:
-  kubeControllerManager:
-    horizontalPodAutoscalerUseRestClients: true
-```
-
-If you've set the above configuration, your cluster is now ready for the custom
-metrics API. Register it via the API aggregation layer. If you're using
 Prometheus, checkout the [custom metrics adapter for Prometheus][k8s-prometheus-custom-metrics-adapter].
 
-## Implementation Details
+[k8s-aggregation-layer]: https://kubernetes.io/docs/tasks/access-kubernetes-api/configure-aggregation-layer/
-
+[k8s-extend-api]: https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/apiserver-aggregation/
-These are the PRs that enable the required configuration:
+[k8s-hpa]: https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/
-
-* [kubernetes/kops#3679][pr-1] - sets `--requestheader-xxx` kube-apiserver flags
-  required to enable aggregation layer
-  ```
-  --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
-  ```
-* [kubernetes/kops#3165][pr-2] - sets `--proxy-client-xxx` kube-apiserver flags
-  required to enable aggregation layer
-  ```
-  --proxy-client-cert-file=<path to aggregator proxy cert>
-  --proxy-client-key-file=<path to aggregator proxy key>
-  ```
-* [kubernetes/kops#3939][pr-3] - add config option to set `--horizontal-pod-
-  autoscaler-use-rest-clients` kube-controller-manager flag required to enable
-  custom metrics
-* [kubernetes/kops#1574][pr-4] - add config options to set `--enable-custom-
-  metrics` flag on master and node kubelets required to enable custom metrics
-
-[k8s-aggregation-layer]: https://v1-9.docs.kubernetes.io/docs/tasks/access-kubernetes-api/configure-aggregation-layer/
-[k8s-extend-api]: https://v1-9.docs.kubernetes.io/docs/concepts/api-extension/apiserver-aggregation/
-[k8s-hpa]: https://v1-9.docs.kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/
 [k8s-metrics-server]: https://github.com/kubernetes/kops/blob/master/addons/metrics-server/README.md
 [k8s-prometheus-custom-metrics-adapter]: https://github.com/DirectXMan12/k8s-prometheus-adapter
-
-[pr-1]: https://github.com/kubernetes/kops/pull/3679
-[pr-2]: https://github.com/kubernetes/kops/pull/3165
-[pr-3]: https://github.com/kubernetes/kops/pull/3939
-[pr-4]: https://github.com/kubernetes/kops/pull/1574
-[pr-5]: https://github.com/kubernetes/kubernetes/pull/55259
-
-[issue-1]: https://github.com/kubernetes/kubernetes/issues/55022