K8S--SVC网络

一、Service网络简介：

Why：pod重启或者重建ip会发生改变，pod之间访问会有问题;
What：解耦了服务和应用。（集群内部服务之间调用填写service域名/IP即可;
How：声明一个service对象

一般常用的有两种：
k8s集群内部的service：selector指定pod，自动创建Endpoints
k8s集群外的service：手动创建Endpoints，指定外部服务的ip、端口和协议。

1.1 k8s 三种网络

node network
pod network
cluster network，也称作virtual IP虚拟网络—service

kube-proxy监听k8s-apiserver,一旦service资源发生变化，kube-proxy就会生成对应的负载调度的调整，这样就保证service的最新状态。

1.2 service类型

ExternalName

Cluster IP

Node Port

Load Balancer

1.3 资源记录

SVC_NAME.NS_NAME.DOMAIN.LTD.
DOMAIN.LTD 集群域名后缀默认为svc.cluster.local.

1.4 service 三种工作模式

　　userspace
　　iptabels
　　ipvs 最新版本

1.4.1 iptables网络模型

1.4.2 ipvs模型

二、实践

2.1 使用清单文件创建cluster IP service资源

apiVersion: v1
kind: Service
metadata:
  name: nginx
  namespace: default
spec:
  selector:
    app: nginx
    role: logstor
  clusterIP: 10.97.97.97    //默认为clusterIP，不指定会自动分配
  type: ClusterIP
  ports:
  - port: 80             //service端口
    targetPort: 80   //容器端口

master yaml]# kubectl   get svc -o wide      //查看创建的SVC
NAME         TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)   AGE   SELECTOR
kubernetes   ClusterIP   10.96.0.1     <none>        443/TCP   28d   <none>
nginx        ClusterIP   10.97.97.97   <none>        80/TCP    13m   app=nginx,role=logstor

2.1.1 资源记录

SVC_NAME.NS_NAME.DOMAIN.LTD.
集群默认后缀DOMAIN.LTD.：svc.cluster.local.

所以上面创建的服务记录为：nginx.default.svc.cluster.local

2.2 使用资源清单创建类型为nodeport的svc

apiVersion: v1
kind: Service
metadata:
  name: myapp
  namespace: default
spec:
  selector:
    app: myapp
    release: canary
  clusterIP: 10.99.99.99
  type: NodePort
  ports:
  - port: 80       //service端口
    targetPort: 80    //pod端口
    nodePort: 30080   //映射节点端口，后续可以直接访问该节点端口，DNAT到service端口，再到pod端口

master yaml]# kubectl   get svc
NAME         TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)        AGE
kubernetes   ClusterIP   10.96.0.1     <none>        443/TCP        28d
myapp        NodePort    10.99.99.99   <none>        80:30080/TCP   38m                 //网络类型为节点网络
nginx        ClusterIP   10.97.97.97   <none>        80/TCP         76m

2.2.1 访问servic

]# curl http://172.18.0.68:30080    //在集群外部机器访问该集群内IP加端口，servie后端须关联pod资源才可以被访问

注：此时可以在节点前面做代理服务器来访问service地址

2.3 Load Balancer（负载均衡器）访问示意图，在Nodeport前面搭建一套负载均衡

参考华为云文档：https://support.huaweicloud.com/usermanual-cce/cce_01_0014.html

apiVersion: v1 
kind: Service 
metadata: 
  annotations:
    kubernetes.io/elb.id: 3c7caa5a-a641-4bff-801a-feace27424b6          # ELB实例ID，替换为实际值
  name: nginx 
spec: 
  ports: 
  - name: service0 
    port: 80
    protocol: TCP 
    targetPort: 80
  selector: 
    app: nginx 
  type: LoadBalancer

三、标签管理

3.1 模拟匹配pod作为后端资源

master yaml]# kubectl  apply -f test.yaml
master yaml]# kubectl  label pods nginx app=nginx
master yaml]# kubectl  describe svc nginx
Name:              nginx
Namespace:         default
Labels:            <none>
Annotations:       kubectl.kubernetes.io/last-applied-configuration:
                     {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"name":"nginx","namespace":"default"},"spec":{"clusterIP":"10.97.97.97","...
Selector:          app=nginx,role=logstor
Type:              ClusterIP
IP:                10.97.97.97
Port:              <unset>  80/TCP
TargetPort:        80/TCP
Endpoints:         <none>         //可以看到当svc标签与pod标签只匹配一个时，service未关联到pod资源
Session Affinity:  None
Events:            <none>

master yaml]# kubectl  label pods nginx role=logstor   //手动匹配所有标签

master yaml]# kubectl   get svc -o wide
NAME         TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)   AGE   SELECTOR
kubernetes   ClusterIP   10.96.0.1     <none>        443/TCP   28d   <none>
nginx        ClusterIP   10.97.97.97   <none>        80/TCP    13m   app=nginx,role=logstor

master yaml]# kubectl  get pods   --show-labels    
NAME                           READY   STATUS    RESTARTS   AGE     LABELS
nginx                          1/1     Running   0          10m     app=nginx,role=logstor      //此时标签已全匹配

master yaml]# kubectl  describe svc nginx       //再次查看发现已匹配后端资源
Name:              nginx
Namespace:         default
Labels:            <none>
Annotations:       kubectl.kubernetes.io/last-applied-configuration:
                     {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"name":"nginx","namespace":"default"},"spec":{"clusterIP":"10.97.97.97","...
Selector:          app=nginx,role=logstor    //svc标签
Type:              ClusterIP
IP:                10.97.97.97
Port:              <unset>  80/TCP
TargetPort:        80/TCP
Endpoints:         10.244.1.84:80     //标签一致，匹配到的后端pod资源
Session Affinity:  None
Events:            <none>

结论：servie根据Selector标签选择器关联pod资源，service的Selector不需要完全匹配pod标签，而pod标签必须完全匹配service标签才可以被关联。

3.2 查看svc关联的pod

]# kubectl   get svc -A
NAMESPACE              NAME                        TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)                  AGE
default                kubernetes                  ClusterIP   10.96.0.1       <none>        443/TCP                  236d
kube-system            kube-dns                    ClusterIP   10.96.0.10      <none>        53/UDP,53/TCP,9153/TCP   236d
kube-system            metrics-server              ClusterIP   10.105.89.199   <none>        443/TCP                  15d
kubernetes-dashboard   dashboard-metrics-scraper   ClusterIP   10.109.95.129   <none>        8000/TCP                 15d
kubernetes-dashboard   kubernetes-dashboard        NodePort    10.98.147.122   <none>        443:30002/TCP            15d
linux40                ng-deploy-80                NodePort    10.97.239.161   <none>        81:30019/TCP             20d

]# kubectl   get pods -n linux40   -o wide
NAME                                READY   STATUS    RESTARTS   AGE   IP            NODE    NOMINATED NODE   READINESS GATES
nginx-deployment-55fb8c9d77-9qlkp   1/1     Running   9          20d   10.244.1.98   node1   <none>           <none>
nginx-deployment-55fb8c9d77-sj8bs   1/1     Running   3          15d   10.244.2.29   node2   <none>           <none>

# 查看endpoint，svc关联的pod资源
]# kubectl   get  ep  -n  linux40
NAME           ENDPOINTS                       AGE
ng-deploy-80   10.244.1.98:80,10.244.2.29:80   20d

四、把来自于同一个客户端的请求始终固定访问同一个pod资源

master yaml]# kubectl patch svc myapp -p ‘{“spec”:{“sessionAffinity”:“ClientIP”}}’

master yaml]# kubectl  describe svc myapp    //查看service详情
Name:                     myapp
Namespace:                default
Labels:                   <none>
Annotations:              kubectl.kubernetes.io/last-applied-configuration:
                            {"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"name":"myapp","namespace":"default"},"spec":{"clusterIP":"10.99.99.99","...
Selector:                 app=myapp,release=canary
Type:                     NodePort
IP:                       10.99.99.99
Port:                     <unset>  80/TCP
TargetPort:               80/TCP
NodePort:                 <unset>  30080/TCP
Endpoints:                10.244.2.84:80   //后端pod资源
Session Affinity:         ClientIP           //此参数说明相同客户端访问相同pod资源；若为“none”则为负载均衡调度。
External Traffic Policy:  Cluster
Events:                   <none>

无头service：将service名称解析到后端pod ip地址来实现访问

apiVersion: v1
kind: Service
metadata:
  name: myapp-svc
  namespace: default
spec:
  selector:
    app: myapp
    release: canary
  clusterIP: "None"    //指定service IP地址为空
  ports:
  - port: 80
    targetPort: 80

master yaml]# kubectl  get svc -n kube-system
NAME       TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)                  AGE
kube-dns   ClusterIP   10.96.0.10   <none>        53/UDP,53/TCP,9153/TCP   29d

master yaml]# dig  -t A myapp-svc.default.svc.cluster.local. @10.96.0.10
 ......
;; ANSWER SECTION:
myapp-svc.default.svc.cluster.local. 30 IN A    10.244.1.97      //可以看到解析SVC资源记录地址为pod地址，当关联到时
myapp-svc.default.svc.cluster.local. 30 IN A    10.244.2.101
myapp-svc.default.svc.cluster.local. 30 IN A    10.244.2.100
myapp-svc.default.svc.cluster.local. 30 IN A    10.244.1.96
myapp-svc.default.svc.cluster.local. 30 IN A    10.244.2.104 
......

master yaml]# kubectl get pods -o wide --show-labels //查看pod标签，与无头service 标签完全匹配
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES LABELS
myapp-deploy-f476f4fcf-jltjs 1/1 Running 3 6d1h 10.244.1.85 k8s-node1 <none> <none> app=myapp,pod-template-hash=f476f4fcf,releas=canary
myapp-deploy-f476f4fcf-nbqwv 1/1 Running 3 6d1h 10.244.2.86 k8s-node2 <none> <none> app=myapp,pod-template-hash=f476f4fcf,releas=canary
nginx 1/1 Running 1 7h26m 10.244.2.85 k8s-node2 <none> <none> app=myapp,release=canary

master yaml]# kubectl get svc -o wide //查看service标签，与pod 标签完全匹配时，可解析service name到pod地址
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 29d <none>
myapp NodePort 10.99.99.99 <none> 80:30080/TCP 7h49m app=myapp,release=canary
myapp-svc ClusterIP None <none> 80/TCP 3m23s app=myapp,release=canary //SVC地址为空
nginx ClusterIP 10.97.97.97 <none> 80/TCP 8h app=nginx,role=logstor

2.5 创建一个hostnetwork类型的pod

2.5.1 不指定DNS策略

apiVersion: v1
kind: Pod
metadata:
  name: nginx-hostnet
spec:
  containers:
  - name: nginx
    image: tomcat-app1:v1
  hostNetwork: true     # 将pod网络和宿主机网络打通

查看网络

]# ifconfig
cali0c474fa1137: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1440
        ether ee:ee:ee:ee:ee:ee  txqueuelen 0  (Ethernet)
        RX packets 1110071  bytes 566024261 (539.8 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1110071  bytes 566024261 (539.8 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

cali4478953ae54: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1440
        ether ee:ee:ee:ee:ee:ee  txqueuelen 0  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

docker0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 172.17.0.1  netmask 255.255.0.0  broadcast 172.17.255.255
        ether 02:42:5f:9c:3d:62  txqueuelen 0  (Ethernet)
        RX packets 1915824  bytes 33663989873 (31.3 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 11088604  bytes 626077036 (597.0 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

ens32: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.64.113  netmask 255.255.255.0  broadcast 192.168.64.255
        inet6 fe80::4b4:9202:aaca:81ec  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:59:02:06  txqueuelen 1000  (Ethernet)
        RX packets 26655124  bytes 18020033636 (16.7 GiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 29230552  bytes 58639418242 (54.6 GiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

]# cat /etc/hosts
# Kubernetes-managed hosts file (host network).
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
192.168.64.110 master-1
192.168.64.111 master-2
192.168.64.112 master-3
192.168.64.113 node1
192.168.64.114 node2
10.103.97.2 apiserver.cluster.local
[root@node1 /]# cat /etc/resolv.conf
nameserver 223.5.5.5
nameserver 223.6.6.6

/]# ping www.baidu.com
PING www.a.shifen.com (182.61.200.6) 56(84) bytes of data.
64 bytes from 182.61.200.6 (182.61.200.6): icmp_seq=1 ttl=128 time=47.8 ms
64 bytes from 182.61.200.6 (182.61.200.6): icmp_seq=2 ttl=128 time=45.7 ms
^C
--- www.a.shifen.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1002ms
rtt min/avg/max/mdev = 45.786/46.821/47.857/1.057 ms

2.5.2 指定dns策略

apiVersion: v1
kind: Pod
metadata:
  name: nginx-hostnet
spec:
  containers:
  - name: nginx
    image: tomcat-app1:v1
  hostNetwork: true     # 将pod网络和宿主机网络打通
  dnsPolicy: ClusterFirstWithHostNet  # DNS策略，使用集群内的dns

查看dns

]# kubectl   get svc -A
NAMESPACE              NAME                          TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)                  AGE
default                kubernetes                    ClusterIP   10.96.0.1        <none>        443/TCP                  3d6h
kube-system            kube-dns                      ClusterIP   10.96.0.10       <none>        53/UDP,53/TCP,9153/TCP   3d6h   # 集群默认dns