Kubernetes Pod是平凡的，它门会被创建，也会死掉（生老病死），并且他们是不可复活的。 ReplicationControllers动态的创建和销毁Pods(比如规模扩大或者缩小，或者执行动态更新)。每个pod都由自己的ip，这些IP也随着时间的变化也不能持续依赖。这样就引发了一个问题：如果一些Pods（让我们叫它作后台，后端）提供了一些功能供其它的Pod使用（让我们叫作前台），在kubernete集群中是如何实现让这些前台能够持续的追踪到这些后台的？

答案是：Service

如图， 一个叫Frontend Deployment的控制器创建了三个pod， pod 的selector labels 为 app=webapp role=frontend version=1.0.0
然后有一个service 指定 标签为 app=webapp role=frontend 的 pod都会被我记录下来。
之后用户访问service就会被负载均衡到各自的pod上，如果pod切换了，service会自己发现。

service 的类型

service 在 K8S中有4种类型

1. clusterIp： 默认类型，自动分配一个仅Cluster 内部可以访问的虚拟ip
2. NodePort：在ClusterIp基础上为servicezai 每台机器上绑定一个端口，这样就可以通过 nodeIp：nodeport来访问服务
3. loadbalancer：在nodeport基础上，借助 cloudprovider 创建一个外部负载均衡器，并将请求转发到 nodeip：nodeport上
4. externalName：把集群外部的服务引入到集群内部来，集群内部可与直接访问。
   

kube-proxy 实现 service代理

K8S集群中，每个node运行一个kube-proxy进程。 kube-proxy负责为service实现一种 vip（虚拟ip）的形式。K8SV1.2 开始默认采用iptables代理 在 k8sV1.14开始默认使用ipvs

代理分类

iptables

iptables 是防火墙里面的数据包转发过滤的一个模块，可以通过配置 DNAT 来进行服务转发

ipvs

svc 工作流程

1. apiServer 用户通过kubectl 命令向apiServer发送创建service的命令。apiServer接收到请求后将数据存储到etcd中
2. kube-proxy 感知到 etcd发生变化，将规则写入到 iptables或者ipvs中
3. iptables 或 ipvs 使用 NAT等技术将 vip的流量转发到真实服务上

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  type: ClusterIP
  selector:
      app: nginx
  ports:
    - name: http
      port: 8080
      targetPort: 8080

创建svc服务

kubectl apply -f service.yaml

就会看到创建了如下的svc

使用 ipvsadm -Ln 命令查看映射关系

所以访问 clusterIp就是负载均衡到旗下的ip去了

如果出现访问不行的情况

==Kubernetes K8S在IPVS代理模式下Service服务的ClusterIP类型访问失败处理 ==

ethtool -K flannel.1 tx-checksum-ip-generic off 

上面那个命令如果运行后就可以访问了，执行

[root@k8s-node02 ~]# vi /etc/systemd/system/k8s-flannel-tx-checksum-off.service
[Unit]
Description=Turn off checksum offload on flannel.1
After=sys-devices-virtual-net-flannel.1.device

[Install]
WantedBy=sys-devices-virtual-net-flannel.1.device

[Service]
Type=oneshot
ExecStart=/sbin/ethtool -K flannel.1 tx-checksum-ip-generic off

开机启动

1 systemctl enable k8s-flannel-tx-checksum-off
2 systemctl start  k8s-flannel-tx-checksum-off

nodeport 模式

只是需要把 type 改成nodeport 就好了

apiVersion: v1
kind: Service
metadata:
  name: my-service-nodeport
spec:
  type: NodePort
  selector:
      app: nginx
  ports:
    - name: http
      port: 8080
      targetPort: 8080

就可以通过外网IP：32180映射到内网的8080

ingress

svc 模式只支持4层代理，需要用ingress才支持7层的通过域名代理的模式

ingress-nginx

安装 ingress-nginx

apiVersion: v1
kind: Namespace
metadata:
  name: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx

---

kind: ConfigMap
apiVersion: v1
metadata:
  name: nginx-configuration
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx

---
kind: ConfigMap
apiVersion: v1
metadata:
  name: tcp-services
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx

---
kind: ConfigMap
apiVersion: v1
metadata:
  name: udp-services
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx

---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: nginx-ingress-serviceaccount
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx

---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRole
metadata:
  name: nginx-ingress-clusterrole
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx
rules:
  - apiGroups:
      - ""
    resources:
      - configmaps
      - endpoints
      - nodes
      - pods
      - secrets
    verbs:
      - list
      - watch
  - apiGroups:
      - ""
    resources:
      - nodes
    verbs:
      - get
  - apiGroups:
      - ""
    resources:
      - services
    verbs:
      - get
      - list
      - watch
  - apiGroups:
      - ""
    resources:
      - events
    verbs:
      - create
      - patch
  - apiGroups:
      - "extensions"
      - "networking.k8s.io"
    resources:
      - ingresses
    verbs:
      - get
      - list
      - watch
  - apiGroups:
      - "extensions"
      - "networking.k8s.io"
    resources:
      - ingresses/status
    verbs:
      - update

---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: Role
metadata:
  name: nginx-ingress-role
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx
rules:
  - apiGroups:
      - ""
    resources:
      - configmaps
      - pods
      - secrets
      - namespaces
    verbs:
      - get
  - apiGroups:
      - ""
    resources:
      - configmaps
    resourceNames:
      # Defaults to "<election-id>-<ingress-class>"
      # Here: "<ingress-controller-leader>-<nginx>"
      # This has to be adapted if you change either parameter
      # when launching the nginx-ingress-controller.
      - "ingress-controller-leader-nginx"
    verbs:
      - get
      - update
  - apiGroups:
      - ""
    resources:
      - configmaps
    verbs:
      - create
  - apiGroups:
      - ""
    resources:
      - endpoints
    verbs:
      - get

---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: RoleBinding
metadata:
  name: nginx-ingress-role-nisa-binding
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: nginx-ingress-role
subjects:
  - kind: ServiceAccount
    name: nginx-ingress-serviceaccount
    namespace: ingress-nginx

---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: nginx-ingress-clusterrole-nisa-binding
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: nginx-ingress-clusterrole
subjects:
  - kind: ServiceAccount
    name: nginx-ingress-serviceaccount
    namespace: ingress-nginx

---

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-ingress-controller
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app.kubernetes.io/name: ingress-nginx
      app.kubernetes.io/part-of: ingress-nginx
  template:
    metadata:
      labels:
        app.kubernetes.io/name: ingress-nginx
        app.kubernetes.io/part-of: ingress-nginx
      annotations:
        prometheus.io/port: "10254"
        prometheus.io/scrape: "true"
    spec:
      serviceAccountName: nginx-ingress-serviceaccount
      containers:
        - name: nginx-ingress-controller
          image: quay.io/kubernetes-ingress-controller/nginx-ingress-controller:0.25.1
          args:
            - /nginx-ingress-controller
            - --configmap=$(POD_NAMESPACE)/nginx-configuration
            - --tcp-services-configmap=$(POD_NAMESPACE)/tcp-services
            - --udp-services-configmap=$(POD_NAMESPACE)/udp-services
            - --publish-service=$(POD_NAMESPACE)/ingress-nginx
            - --annotations-prefix=nginx.ingress.kubernetes.io
          securityContext:
            allowPrivilegeEscalation: true
            capabilities:
              drop:
                - ALL
              add:
                - NET_BIND_SERVICE
            # www-data -> 33
            runAsUser: 33
          env:
            - name: POD_NAME
              valueFrom:
                fieldRef:
                  fieldPath: metadata.name
            - name: POD_NAMESPACE
              valueFrom:
                fieldRef:
                  fieldPath: metadata.namespace
          ports:
            - name: http
              containerPort: 80
            - name: https
              containerPort: 443
          livenessProbe:
            failureThreshold: 3
            httpGet:
              path: /healthz
              port: 10254
              scheme: HTTP
            initialDelaySeconds: 10
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 10
          readinessProbe:
            failureThreshold: 3
            httpGet:
              path: /healthz
              port: 10254
              scheme: HTTP
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 10

---

在创建一个 service-nodeport.yaml

apiVersion: v1
kind: Service
metadata:
  name: ingress-nginx
  namespace: ingress-nginx
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx
spec:
  type: NodePort
  ports:
    - name: http
      port: 80
      targetPort: 80
      protocol: TCP
    - name: https
      port: 443
      targetPort: 443
      protocol: TCP
  selector:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/part-of: ingress-nginx

---

现在有一个service

想要通过ingress 暴露域名访问，首先创建一个ingress

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: my-ingress
spec:
  rules:
    - host: foo.bar.com
      http:
        paths:
          - path: /
            backend:
              serviceName: my-service
              servicePort: 8080

使用 kubectl apply -f ingress.yaml 创建ingress。

这时候访问 foo.bar.com:32404/test ingress 就会把请求转到 my-service 的8080端口，然后my-service在通过ipvs寻找pod转发请求

使用ingress实现一个虚拟主机

1. 创建两个deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment-01
spec:
  replicas: 2
  selector:
    matchLabels:
      app: v1
  template:
    metadata:
      labels:
        app: v1
    spec:
      containers:
      - name: zc-deploy-01
        image: zhucheng1992/myboot:1.0
        ports:
        - containerPort: 8080

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment-02
spec:
  replicas: 2
  selector:
    matchLabels:
      app: v2
  template:
    metadata:
      labels:
        app: v2
    spec:
      containers:
      - name: zc-deploy-02
        image: zhucheng1992/myboot:2.0
        ports:
        - containerPort: 8080

2. 创建两个svc

apiVersion: v1
kind: Service
metadata:
  name: my-service-01
spec:
  type: ClusterIP
  selector:
      app: v1
  ports:
    - name: http
      port: 8080
      targetPort: 8080
---
apiVersion: v1
kind: Service
metadata:
  name: my-service-02
spec:
  type: ClusterIP
  selector:
      app: v2
  ports:
    - name: http
      port: 8080
      targetPort: 8080

3. 创建一个ingress

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: my-ingress-01
spec:
  rules:
    - host: www.zc1.com
      http:
        paths:
          - path: /
            backend:
              serviceName: my-service-01
              servicePort: 8080
---
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: my-ingress-02
spec:
  rules:
    - host: www.zc2.com
      http:
        paths:
          - path: /
            backend:
              serviceName: my-service-02
              servicePort: 8080

headless svc 无头服务

apiVersion: v1
kind: Service
metadata:
  name: headless-svc
spec:
  selector:
    app: myapp
  clusterIP: "None"
  ports:
    - port: 80
      targetPort: 80

找到coreDNS 的ip地址

使用

dig -t A headless-svc.default.svc.cluster.local. @10.244.0.20
dig -t A 无头服务名称.命名空间.集群名称. @coreDNSip 

无头服务中，还是可以通过访问域名的方案访问pod