Service 的概念
Kubernetes  Service  定义了这样一种抽象:一个  Pod  的逻辑分组,一种可以访问它们的策略 —— 通常称为微
服务。 这一组  Pod  能够被  Service  访问到,通常是通过  Label Selector

 

 

Service能够提供负载均衡的能力,但是在使用上有以下限制:
只提供 4 层负载均衡能力,而没有 7 层功能,但有时我们可能需要更多的匹配规则来转发请求,这点上 4 层负载均衡是不支持的

Service 的类型
Service 在 K8s 中有以下四种类型

  • ClusterIp:默认类型,自动分配一个仅 Cluster 内部可以访问的虚拟 IP
  • NodePort:在 ClusterIP 基础上为 Service 在每台机器上绑定一个端口,这样就可以通过 : NodePort 来访问该服务
  • LoadBalancer:在 NodePort 的基础上,借助 cloud provider 创建一个外部负载均衡器,并将请求转发到: NodePort
  • ExternalName:把集群外部的服务引入到集群内部来,在集群内部直接使用。没有任何类型代理被创建,这只有 kubernetes 1.7 或更高版本的 kube-dns 才支持

 

 

VIP 和 Service 代理

在 Kubernetes 集群中,每个 Node 运行一个  kube-proxy  进程。 kube-proxy  负责为  Service  实现了一种
VIP(虚拟 IP)的形式,而不是  ExternalName  的形式。 在 Kubernetes v1.0 版本,代理完全在 userspace。在
Kubernetes v1.1 版本,新增了 iptables 代理,但并不是默认的运行模式。 从 Kubernetes v1.2 起,默认就是
iptables 代理。 在 Kubernetes v1.8.0-beta.0 中,添加了 ipvs 代理。

在 Kubernetes 1.14 版本开始默认使用 ipvs 代理。

在 Kubernetes v1.0 版本, Service 是 “4层”(TCP/UDP over IP)概念。 在 Kubernetes v1.1 版本,新增了
Ingress API(beta 版),用来表示 “7层”(HTTP)服务。

代理模式的分类

Ⅰ、userspace 代理模式

 

 Ⅱ、iptables 代理模式

 Ⅲ、ipvs 代理模式

这种模式,kube-proxy 会监视 Kubernetes Service 对象和 Endpoints ,调用 netlink 接口以相应地创建
ipvs 规则并定期与 Kubernetes Service 对象和 Endpoints 对象同步 ipvs 规则,以确保 ipvs 状态与期望一
致。访问服务时,流量将被重定向到其中一个后端 Pod
与 iptables 类似,ipvs 于 netfilter 的 hook 功能,但使用哈希表作为底层数据结构并在内核空间中工作。这意
味着 ipvs 可以更快地重定向流量,并且在同步代理规则时具有更好的性能。此外,ipvs 为负载均衡算法提供了更
多选项,例如:
rr :轮询调度
lc :最小连接数
dh :目标哈希
sh :源哈希
sed :最短期望延迟
nq : 不排队调度

ClusterIP
clusterIP 主要在每个 node 节点使用 iptables,将发向 clusterIP 对应端口的数据,转发到 kube-proxy 中。然
后 kube-proxy 自己内部实现有负载均衡的方法,并可以查询到这个 service 下对应 pod 的地址和端口,进而把
数据转发给对应的 pod 的地址和端口

 

 

为了实现图上的功能,主要需要以下几个组件的协同工作:
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
kube-proxy kubernetes的每个节点中都有一个叫做kube-porxy的进程,这个进程负责感知service,pod
的变化,并将变化的信息写入本地的iptables规则中
iptables 使用NAT等技术将virtualIP的流量转至endpoint中

[root@k8s-master mnt]# kubectl get svc
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP   3d23h
[root@k8s-master mnt]# ipvsadm -L
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  10.96.0.1:https rr
  -> 192.168.180.130:sun-sr-https Masq    1      3          0
TCP  10.96.0.10:domain rr
  -> 10.244.0.6:domain            Masq    1      0          0
  -> 10.244.0.7:domain            Masq    1      0          0
TCP  10.96.0.10:9153 rr
  -> 10.244.0.6:9153              Masq    1      0          0
  -> 10.244.0.7:9153              Masq    1      0          0
UDP  10.96.0.10:domain rr
  -> 10.244.0.6:domain            Masq    1      0          0
  -> 10.244.0.7:domain            Masq    1      0          0
[root@k8s-master mnt]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  10.96.0.1:443 rr
  -> 192.168.180.130:6443         Masq    1      3          0
TCP  10.96.0.10:53 rr
  -> 10.244.0.6:53                Masq    1      0          0
  -> 10.244.0.7:53                Masq    1      0          0
TCP  10.96.0.10:9153 rr
  -> 10.244.0.6:9153              Masq    1      0          0
  -> 10.244.0.7:9153              Masq    1      0          0
UDP  10.96.0.10:53 rr
  -> 10.244.0.6:53                Masq    1      0          0
  -> 10.244.0.7:53                Masq    1      0          0

 可以看出访问的试本机6443端口

yaml文件

[root@k8s-master mnt]# cat svc-deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-deploy
  namespace: default
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
      release: stabel
  template:
    metadata:
      labels:
        app: myapp
        release: stabel
        env: test
    spec:
      containers:
      - name: myapp
        image: wangyanglinux/myapp:v2
        imagePullPolicy: IfNotPresent
        ports:
        - name: http
          containerPort: 80
[root@k8s-master mnt]# cat myapp-service.yaml
apiVersion: v1
kind: Service
metadata:
  name: myapp
  namespace: default
spec:
  type: ClusterIP
  selector:
    app: myapp
    release: stabel
  ports:
  - name: http
    port: 80
    targetPort: 80
[root@k8s-master mnt]#

 测试

[root@k8s-master mnt]# vim svc-deployment.yaml
[root@k8s-master mnt]# kubectl apply -f svc-deployment.yaml
deployment.apps/myapp-deploy created
[root@k8s-master mnt]# kubectl get pod
NAME                            READY   STATUS              RESTARTS   AGE
myapp-deploy-55c8657767-5jzt4   1/1     Running             0          5s
myapp-deploy-55c8657767-6tkc4   0/1     ContainerCreating   0          5s
myapp-deploy-55c8657767-hw96w   0/1     ContainerCreating   0          5s
[root@k8s-master mnt]# kubectl get pod
NAME                            READY   STATUS    RESTARTS   AGE
myapp-deploy-55c8657767-5jzt4   1/1     Running   0          12s
myapp-deploy-55c8657767-6tkc4   1/1     Running   0          12s
myapp-deploy-55c8657767-hw96w   1/1     Running   0          12s
[root@k8s-master mnt]# kubectl get pod
NAME                            READY   STATUS    RESTARTS   AGE
myapp-deploy-55c8657767-5jzt4   1/1     Running   0          13s
myapp-deploy-55c8657767-6tkc4   1/1     Running   0          13s
myapp-deploy-55c8657767-hw96w   1/1     Running   0          13s
[root@k8s-master mnt]# kubectl get pod -o wide
NAME                            READY   STATUS    RESTARTS   AGE   IP            NODE         NOMINATED NODE   READINESS GATES
myapp-deploy-55c8657767-5jzt4   1/1     Running   0          17s   10.244.1.26   k8s-node02   <none>           <none>
myapp-deploy-55c8657767-6tkc4   1/1     Running   0          17s   10.244.2.29   k8s-node01   <none>           <none>
myapp-deploy-55c8657767-hw96w   1/1     Running   0          17s   10.244.2.30   k8s-node01   <none>           <none>
[root@k8s-master mnt]# curl 10.244.2.30
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
[root@k8s-master mnt]# vim myapp-service.yaml
[root@k8s-master mnt]# kubectl create -f  myapp-service.yaml
service/myapp created
[root@k8s-master mnt]# kubectl get svc
NAME         TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.96.0.1        <none>        443/TCP   3d23h
myapp        ClusterIP   10.111.227.210   <none>        80/TCP    5s
[root@k8s-master mnt]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  10.96.0.1:443 rr
  -> 192.168.180.130:6443         Masq    1      3          0
TCP  10.96.0.10:53 rr
  -> 10.244.0.6:53                Masq    1      0          0
  -> 10.244.0.7:53                Masq    1      0          0
TCP  10.96.0.10:9153 rr
  -> 10.244.0.6:9153              Masq    1      0          0
  -> 10.244.0.7:9153              Masq    1      0          0
TCP  10.111.227.210:80 rr
  -> 10.244.1.26:80               Masq    1      0          0
  -> 10.244.2.29:80               Masq    1      0          0
  -> 10.244.2.30:80               Masq    1      0          0
UDP  10.96.0.10:53 rr
  -> 10.244.0.6:53                Masq    1      0          0
  -> 10.244.0.7:53                Masq    1      0          0
[root@k8s-master mnt]# curl 10.111.227.210
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
[root@k8s-master mnt]# curl 10.111.227.210
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
[root@k8s-master mnt]# curl 10.111.227.210
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
[root@k8s-master mnt]# curl 10.111.227.210/hostname.html
myapp-deploy-55c8657767-hw96w
[root@k8s-master mnt]# curl 10.111.227.210/hostname.html
myapp-deploy-55c8657767-6tkc4
[root@k8s-master mnt]# curl 10.111.227.210/hostname.html
myapp-deploy-55c8657767-5jzt4
[root@k8s-master mnt]# curl 10.111.227.210/hostname.html
myapp-deploy-55c8657767-hw96w
[root@k8s-master mnt]# curl 10.111.227.210/hostname.html
myapp-deploy-55c8657767-6tkc4
[root@k8s-master mnt]# curl 10.111.227.210/hostname.html
myapp-deploy-55c8657767-5jzt4
[root@k8s-master mnt]# curl 10.111.227.210/hostname.html
myapp-deploy-55c8657767-hw96w

Headless Service
有时不需要或不想要负载均衡,以及单独的 Service IP 。遇到这种情况,可以通过指定 Cluster
IP(spec.clusterIP) 的值为 “None” 来创建 Headless Service 。这类 Service 并不会分配 Cluster IP, kube-
proxy 不会处理它们,而且平台也不会为它们进行负载均衡和路由。

[root@k8s-master mnt]# cat svc-headless.yaml
apiVersion: v1
kind: Service
metadata:
  name: myapp-headless
  namespace: default
spec:
  selector:
    app: myapp
  clusterIP: "None"
  ports:
  - port: 80
    targetPort: 80
[root@k8s-master mnt]#
[root@k8s-master mnt]# vim svc-headless.yaml
[root@k8s-master mnt]# kubectl create -f svc-headless.yaml
service/myapp-headless created
[root@k8s-master mnt]# kube
kubeadm  kubectl  kubelet
[root@k8s-master mnt]# kubectl get svc
NAME             TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE
kubernetes       ClusterIP   10.96.0.1        <none>        443/TCP   3d23h
myapp            ClusterIP   10.111.227.210   <none>        80/TCP    8m
myapp-headless   ClusterIP   None             <none>        80/TCP    7s
[root@k8s-master mnt]# kubectl create -f svc-headless.yaml
Error from server (AlreadyExists): error when creating "svc-headless.yaml": services "myapp-headless" already exists
[root@k8s-master mnt]# kubectl get pod -n kube-system
NAME                                 READY   STATUS    RESTARTS   AGE
coredns-58cc8c89f4-9gn5g             1/1     Running   2          3d23h
coredns-58cc8c89f4-xxzx7             1/1     Running   2          3d23h
etcd-k8s-master                      1/1     Running   3          3d23h
kube-apiserver-k8s-master            1/1     Running   3          3d23h
kube-controller-manager-k8s-master   1/1     Running   6          3d23h
kube-flannel-ds-amd64-4bc88          1/1     Running   3          3d23h
kube-flannel-ds-amd64-lzwd6          1/1     Running   4          3d23h
kube-flannel-ds-amd64-vw4vn          1/1     Running   5          3d23h
kube-proxy-bs8sd                     1/1     Running   3          3d23h
kube-proxy-nfvtt                     1/1     Running   2          3d23h
kube-proxy-rn98b                     1/1     Running   3          3d23h
kube-scheduler-k8s-master            1/1     Running   5          3d23h
[root@k8s-master mnt]# dig
;; Warning: Message parser reports malformed message packet.

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-9.P2.el7 <<>>
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 326
;; flags: qr rd ra; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 27
;; WARNING: Message has 8 extra bytes at end

;; QUESTION SECTION:
;.                              IN      NS

;; ANSWER SECTION:
.                       5       IN      NS      h.root-servers.net.
.                       5       IN      NS      e.root-servers.net.
.                       5       IN      NS      d.root-servers.net.
.                       5       IN      NS      m.root-servers.net.
.                       5       IN      NS      k.root-servers.net.
.                       5       IN      NS      g.root-servers.net.
.                       5       IN      NS      l.root-servers.net.
.                       5       IN      NS      c.root-servers.net.
.                       5       IN      NS      j.root-servers.net.
.                       5       IN      NS      i.root-servers.net.
.                       5       IN      NS      f.root-servers.net.
.                       5       IN      NS      b.root-servers.net.
.                       5       IN      NS      a.root-servers.net.

;; ADDITIONAL SECTION:
a.root-servers.net.     5       IN      A       198.41.0.4
b.root-servers.net.     5       IN      A       199.9.14.201
c.root-servers.net.     5       IN      A       192.33.4.12
d.root-servers.net.     5       IN      A       199.7.91.13
e.root-servers.net.     5       IN      A       192.203.230.10
f.root-servers.net.     5       IN      A       192.5.5.241
g.root-servers.net.     5       IN      A       192.112.36.4
h.root-servers.net.     5       IN      A       198.97.190.53
i.root-servers.net.     5       IN      A       192.36.148.17
j.root-servers.net.     5       IN      A       192.58.128.30
k.root-servers.net.     5       IN      A       193.0.14.129
l.root-servers.net.     5       IN      A       199.7.83.42
m.root-servers.net.     5       IN      A       202.12.27.33
a.root-servers.net.     5       IN      AAAA    2001:503:ba3e::2:30
b.root-servers.net.     5       IN      AAAA    2001:500:200::b

;; Query time: 6 msec
;; SERVER: 192.168.180.2#53(192.168.180.2)
;; WHEN: 一 12月 23 22:16:55 CST 2019
;; MSG SIZE  rcvd: 512

[root@k8s-master mnt]# kubectl get pod -n kube-system -o wide
NAME                                 READY   STATUS    RESTARTS   AGE     IP                NODE         NOMINATED NODE   READINESS GATES
coredns-58cc8c89f4-9gn5g             1/1     Running   2          3d23h   10.244.0.7        k8s-master   <none>           <none>
coredns-58cc8c89f4-xxzx7             1/1     Running   2          3d23h   10.244.0.6        k8s-master   <none>           <none>
etcd-k8s-master                      1/1     Running   3          3d23h   192.168.180.130   k8s-master   <none>           <none>
kube-apiserver-k8s-master            1/1     Running   3          3d23h   192.168.180.130   k8s-master   <none>           <none>
kube-controller-manager-k8s-master   1/1     Running   6          3d23h   192.168.180.130   k8s-master   <none>           <none>
kube-flannel-ds-amd64-4bc88          1/1     Running   3          3d23h   192.168.180.136   k8s-node02   <none>           <none>
kube-flannel-ds-amd64-lzwd6          1/1     Running   4          3d23h   192.168.180.130   k8s-master   <none>           <none>
kube-flannel-ds-amd64-vw4vn          1/1     Running   5          3d23h   192.168.180.135   k8s-node01   <none>           <none>
kube-proxy-bs8sd                     1/1     Running   3          3d23h   192.168.180.135   k8s-node01   <none>           <none>
kube-proxy-nfvtt                     1/1     Running   2          3d23h   192.168.180.136   k8s-node02   <none>           <none>
kube-proxy-rn98b                     1/1     Running   3          3d23h   192.168.180.130   k8s-master   <none>           <none>
kube-scheduler-k8s-master            1/1     Running   5          3d23h   192.168.180.130   k8s-master   <none>           <none>
[root@k8s-master mnt]# dig -t A myapp-headless.default.svc.cluster.local. @10.244.0.7

; <<>> DiG 9.11.4-P2-RedHat-9.11.4-9.P2.el7 <<>> -t A myapp-headless.default.svc.cluster.local. @10.244.0.7
;; global options: +cmd
;; Got answer:
;; WARNING: .local is reserved for Multicast DNS
;; You are currently testing what happens when an mDNS query is leaked to DNS
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44455
;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;myapp-headless.default.svc.cluster.local. IN A

;; ANSWER SECTION:
myapp-headless.default.svc.cluster.local. 30 IN A 10.244.2.29
myapp-headless.default.svc.cluster.local. 30 IN A 10.244.1.26
myapp-headless.default.svc.cluster.local. 30 IN A 10.244.2.30

;; Query time: 199 msec
;; SERVER: 10.244.0.7#53(10.244.0.7)
;; WHEN: 一 12月 23 22:18:21 CST 2019
;; MSG SIZE  rcvd: 237

[root@k8s-master mnt]# kubectl get pod -o wide
NAME                            READY   STATUS    RESTARTS   AGE   IP            NODE         NOMINATED NODE   READINESS GATES
myapp-deploy-55c8657767-5jzt4   1/1     Running   0          16m   10.244.1.26   k8s-node02   <none>           <none>
myapp-deploy-55c8657767-6tkc4   1/1     Running   0          16m   10.244.2.29   k8s-node01   <none>           <none>
myapp-deploy-55c8657767-hw96w   1/1     Running   0          16m   10.244.2.30   k8s-node01   <none>           <none>

NodePort
nodePort 的原理在于在 node 上开了一个端口,将向该端口的流量导入到 kube-proxy,然后由 kube-proxy 进
一步到给对应的 pod。

[root@k8s-master mnt]# cat NodePort.yaml
apiVersion: v1
kind: Service
metadata:
  name: myapp
  namespace: default
spec:
  type: NodePort
  selector:
    app: myapp
    release: stabel
  ports:
  - name: http
    port: 80
    targetPort: 80
[root@k8s-master mnt]#

测试:

[root@k8s-master mnt]# vim NodePort.yaml
[root@k8s-master mnt]# kubectl create -f NodePort.yaml
Error from server (AlreadyExists): error when creating "NodePort.yaml": services "myapp" already exists
[root@k8s-master mnt]# kubectl apply -f NodePort.yaml
Warning: kubectl apply should be used on resource created by either kubectl create --save-config or kubectl apply
service/myapp configured
[root@k8s-master mnt]# kubectl get svc
NAME             TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
kubernetes       ClusterIP   10.96.0.1        <none>        443/TCP        4d
myapp            NodePort    10.111.227.210   <none>        80:31103/TCP   14m
myapp-headless   ClusterIP   None             <none>        80/TCP         6m26s
[root@k8s-master mnt]# netstat -antp |grep 31103
tcp6       0      0 :::31103                :::*                    LISTEN      3974/kube-proxy
[root@k8s-master mnt]#

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