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。
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，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 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：
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： 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：
$ 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"]}]}