kubernetes-handbook/concepts/custom-metrics-hpa.md

# 自定义指标HPA

Kubernetes中不仅支持CPU、内存为指标的HPA，还支持自定义指标的HPA，例如QPS。

本文中使用的yaml文件见[manifests/HPA](https://github.com/rootsongjc/kubernetes-handbook/tree/master/manifests/HPA)。

## 设置自定义指标

**kubernetes1.6**

> 在kubernetes1.6集群中配置自定义指标的HPA的说明已废弃。

在设置定义指标HPA之前需要先进行如下配置：

- 将heapster的启动参数 `--api-server` 设置为 true


- 启用custom metric API
- 将kube-controller-manager的启动参数中`--horizontal-pod-autoscaler-use-rest-clients`设置为true，并指定`--master`为API server地址，如`--master=http://172.20.0.113:8080`

在kubernetes1.5以前很容易设置，参考[1.6以前版本的kubernetes中开启自定义HPA](https://medium.com/@marko.luksa/kubernetes-autoscaling-based-on-custom-metrics-without-using-a-host-port-b783ed6241ac)，而在1.6中因为取消了原来的annotation方式设置custom metric，只能通过API server和kube-aggregator来获取custom metric，因为只有两种方式来设置了，一是直接通过API server获取heapster的metrics，二是部署[kube-aggragator](https://github.com/kubernetes/kube-aggregator)来实现。

我们将在kubernetes1.8版本的kubernetes中，使用聚合的API server来实现自定义指标的HPA。

**kuberentes1.7+**

确认您的kubernetes版本在1.7或以上，修改以下配置：

- 将kube-controller-manager的启动参数中`--horizontal-pod-autoscaler-use-rest-clients`设置为true，并指定`--master`为API server地址，如`--master=http://172.20.0.113:8080
- 修改kube-apiserver的配置文件apiserver，增加一条配置`--requestheader-client-ca-file=/etc/kubernetes/ssl/ca.pem --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=/etc/kubernetes/ssl/kubernetes.pem --proxy-client-key-file=/etc/kubernetes/ssl/kubernetes-key.pem`，用来配置aggregator的CA证书。

已经内置了`apiregistration.k8s.io/v1beta1` API，可以直接定义APIService，如：

```yaml
apiVersion: apiregistration.k8s.io/v1
kind: APIService
metadata:
  name: v1.custom-metrics.metrics.k8s.io
spec:
  insecureSkipTLSVerify: true
  group: custom-metrics.metrics.k8s.io
  groupPriorityMinimum: 1000
  versionPriority: 5
  service:
    name: api
    namespace: custom-metrics
  version: v1alpha1
```

**部署Prometheus**

使用[prometheus-operator.yaml](https://github.com/rootsongjc/kubernetes-handbook/blob/master/manifests/HPA/prometheus-operator.yaml)文件部署Prometheus operator。

**注意：**将镜像修改为你自己的镜像仓库地址。

这产生一个自定义的API：<http://172.20.0.113:8080/apis/custom-metrics.metrics.k8s.io/v1alpha1>，可以通过浏览器访问，还可以使用下面的命令可以检查该API：

```bash
$ kubectl get --raw=apis/custom-metrics.metrics.k8s.io/v1alpha1
{"kind":"APIResourceList","apiVersion":"v1","groupVersion":"custom-metrics.metrics.k8s.io/v1alpha1","resources":[{"name":"jobs.batch/http_requests","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"namespaces/http_requests","singularName":"","namespaced":false,"kind":"MetricValueList","verbs":["get"]},{"name":"jobs.batch/up","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"pods/up","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"services/scrape_samples_scraped","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"namespaces/scrape_samples_scraped","singularName":"","namespaced":false,"kind":"MetricValueList","verbs":["get"]},{"name":"pods/scrape_duration_seconds","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"services/scrape_duration_seconds","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"pods/http_requests","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"pods/scrape_samples_post_metric_relabeling","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"jobs.batch/scrape_samples_scraped","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"jobs.batch/scrape_duration_seconds","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"namespaces/scrape_duration_seconds","singularName":"","namespaced":false,"kind":"MetricValueList","verbs":["get"]},{"name":"namespaces/scrape_samples_post_metric_relabeling","singularName":"","namespaced":false,"kind":"MetricValueList","verbs":["get"]},{"name":"services/scrape_samples_post_metric_relabeling","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"services/up","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"pods/scrape_samples_scraped","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"services/http_requests","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"jobs.batch/scrape_samples_post_metric_relabeling","singularName":"","namespaced":true,"kind":"MetricValueList","verbs":["get"]},{"name":"namespaces/up","singularName":"","namespaced":false,"kind":"MetricValueList","verbs":["get"]}]}
```

## 参考

- [1.6以前版本的kubernetes中开启自定义HPA](https://medium.com/@marko.luksa/kubernetes-autoscaling-based-on-custom-metrics-without-using-a-host-port-b783ed6241ac)
- [1.7版本的kubernetes中启用自定义HPA](https://docs.bitnami.com/kubernetes/how-to/configure-autoscaling-custom-metrics/)
- [Horizontal Pod Autoscaler Walkthrough](https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale-walkthrough/)
- [Kubernetes 1.8: Now with 100% Daily Value of Custom Metrics](https://blog.openshift.com/kubernetes-1-8-now-custom-metrics/)
- [Arbitrary/Custom Metrics in the Horizontal Pod Autoscaler#117](https://github.com/kubernetes/features/issues/117)