kubernetes的服務對外暴露通常有三種方式分別為nodeport、loadbalancer和ingress。nodeport很容易理解就是在每個主機上面啟動一個服務埠暴露出去，這樣弊端是造成埠浪費；loadbalancer這種方式目前只能在gce的平臺跑的很好，就是在叢集之外對接雲平臺的負載均衡；還有從kubernetes1.2出來的ingress，他是通過在計算結算啟動一個軟負載均衡（Nginx、Haproxy）轉發流量。
在第一篇我想先介紹安裝使用。
先啟動一個後端服務：

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: default-http
 
-backend
  labels:
    k8s-app: default-http-backend
  namespace: kube-system
spec:
  replicas: 1
  template:
    metadata:
      labels:
        k8s-app: default-http-backend
    spec:
      terminationGracePeriodSeconds: 60
      nodeName: slave2
      containers:
      - name: default-http-backend
 

        image: gcr.io/google_containers/defaultbackend:1.0
        imagePullPolicy: IfNotPresent
        livenessProbe:
          httpGet:
            path: /healthz
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 30
          timeoutSeconds: 5
        ports:
        - containerPort: 8080
 

        resources:
          limits:
            cpu: 10m
            memory: 20Mi
          requests:
            cpu: 10m
            memory: 20Mi
---
apiVersion: v1
kind: Service
metadata:
  name: default-http-backend
  namespace: kube-system
  labels:
    k8s-app: default-http-backend
spec:
  ports:
  - port: 80
    targetPort: 8080
  selector:
    k8s-app: default-http-backend

由於我機器有限，我就在指定的節點啟動這個後端服務，這個服務啟動80埠，提供預設的服務連線。驗證一下：

curl  10.254.12.58:80
default backend - 404

然後ingress controller，它本質就是一個負載均衡配置器

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-ingress-controller
  labels:
    k8s-app: nginx-ingress-controller
  namespace: kube-system
spec:
  replicas: 1
  template:
    metadata:
      labels:
        k8s-app: nginx-ingress-controller
      annotations:
        prometheus.io/port: '10254'
        prometheus.io/scrape: 'true'
    spec:
      terminationGracePeriodSeconds: 60
      nodeName: slave1
      containers:
      - image: docker.io/chancefocus/nginx-ingress-controller
        imagePullPolicy: IfNotPresent
        name: nginx-ingress-controller
        readinessProbe:
          httpGet:
            path: /healthz
            port: 10254
            scheme: HTTP
        livenessProbe:
          httpGet:
            path: /healthz
            port: 10254
            scheme: HTTP
          initialDelaySeconds: 10
          timeoutSeconds: 1
        ports:
        - containerPort: 80
          hostPort: 80
        - containerPort: 443
          hostPort: 443
        env:
          - name: POD_NAME
            valueFrom:
              fieldRef:
                fieldPath: metadata.name
          - name: POD_NAMESPACE
            valueFrom:
              fieldRef:
                fieldPath: metadata.namespace
        args:
        - /nginx-ingress-controller
        - --default-backend-service=kube-system/default-http-backend
        - --apiserver-host=http://10.39.0.6:8080

ingress-controller會同步k8s的資源修改負載均衡規則，然後就可以建立一個負載均衡規則了

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: test
  namespace: kube-system
  annotations:
    ingress.kubernetes.io/force-ssl-redirect: "false"
    ingress.kubernetes.io/ssl-redirect: "false"
spec:
  rules:
  - http:
      paths:
      - path: /api
        backend:
          serviceName: heapster
          servicePort: 80

把/api的請求轉發到heapster這個service裡面。其中和http平級的還有一個引數
- host: xx.xxx.xxx，註明域名
下面是來自google的解說圖片

下面就可以測試了：
首先確認服務是ok的，10.254.51.153是clusterIP，192.168.90.6是容器的IP

curl http://10.254.51.153/api/v1/model/namespaces/default/pods/busybox-1865195333-zkwtt/containers/busybox/metrics/cpu/usage
{
  "metrics": [
   {
    "timestamp": "2017-04-20T02:20:00Z",
    "value": 7412767
   },
   {
    "timestamp": "2017-04-20T02:21:00Z",
    "value": 7412767
   },
   {
    "timestamp": "2017-04-20T02:22:00Z",
    "value": 7412767
   }
  ],
  "latestTimestamp": "2017-04-20T02:22:00Z"
 }
 curl http://192.168.90.6:8082/api/v1/model/namespaces/default/pods/busybox-1865195333-zkwtt/containers/busybox/metrics/cpu/usage
{
  "metrics": [
   {
    "timestamp": "2017-04-20T02:44:00Z",
    "value": 8960064
   },
   {
    "timestamp": "2017-04-20T02:45:00Z",
    "value": 8960064
   },
   {
    "timestamp": "2017-04-20T02:46:00Z",
    "value": 8960064
   }
  ],
  "latestTimestamp": "2017-04-20T02:46:00Z"
 }

然後在任何一臺機器上面的都可以通過slave1上面的80埠訪問服務了

 curl http://10.39.0.17/api/v1/model/namespaces/default/pods/busybox-1865195333-zkwtt/containers/busybox/metrics/cpu/usage
{
  "metrics": [
   {
    "timestamp": "2017-04-20T02:42:00Z",
    "value": 8960064
   },
   {
    "timestamp": "2017-04-20T02:43:00Z",
    "value": 8960064
   }
  ],
  "latestTimestamp": "2017-04-20T02:43:00Z"
 }

這兒埠80就可以重用了。再進入容器看看，nginx.conf檔案：

    upstream kube-system-heapster-80 {
        least_conn;
        server 192.168.90.6:8082 max_fails=0 fail_timeout=0;
    }
    upstream upstream-default-backend {
        least_conn;
        server 192.168.90.2:8080 max_fails=0 fail_timeout=0;
    }

location /api {
            set $proxy_upstream_name "kube-system-heapster-80";

location / {
            set $proxy_upstream_name "upstream-default-backend";

可以看到其實就是修改了Nginx的配置達到服務轉發的效果。ok，基本按照使用已經瞭解了，其中有個細節就是為啥轉發upstream是的容器地址而不是service的地址，有兩個主要原因：第一，多次轉發降低效率，第二，為了保持session，如果通過service會做輪訓，無法保持session。接下來的blog將進行程式碼詳細講解。