自定義指標HPA
Kubernetes中不僅支持CPU、內存為指標的HPA，還支持自定義指標的HPA，例如QPS。
本文中使用的yaml文件見manifests/HPA。
設置自定義指標
kubernetes1.6
在kubernetes1.6集群中配置自定義指標的HPA的說明已廢棄。
在設置定義指標HPA之前需要先進行如下配置：
- 將heapster的啟動參數
--api-server設置為 true
- 啟用custom metric API
- 將kube-controller-manager的啟動參數中
--horizontal-pod-autoscaler-use-rest-clients設置為true，並指定--master為API server地址，如--master=http://172.20.0.113:8080
在kubernetes1.5以前很容易設置，參考1.6以前版本的kubernetes中開啟自定義HPA，而在1.6中因為取消了原來的annotation方式設置custom metric，只能通過API server和kube-aggregator來獲取custom metric，因為只有兩種方式來設置了，一是直接通過API server獲取heapster的metrics，二是部署kube-aggragator來實現。
我們將在kubernetes1.8版本的kubernetes中，使用聚合的API server來實現自定義指標的HPA。
kuberentes1.7+
確認您的kubernetes版本在1.7或以上，修改以下配置：
- 將kube-controller-manager的啟動參數中
--horizontal-pod-autoscaler-use-rest-clients設置為true，並指定--master為API server地址，如`--master=http://172.20.0.113:8080 - 修改kube-apiserver的配置文件apiserver，增加一條配置
--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，用來配置aggregator的CA證書。
已經內置了apiregistration.k8s.io/v1beta1 API，可以直接定義APIService，如：
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文件部署Prometheus operator。
注意：將鏡像修改為你自己的鏡像倉庫地址。
這產生一個自定義的API：http://172.20.0.113:8080/apis/custom-metrics.metrics.k8s.io/v1alpha1，可以通過瀏覽器訪問，還可以使用下面的命令可以檢查該API：
$ 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"