在k8s上是如何发布服务的

kubenetes-service

1、什么是Service
2、定义一个Service
3、使用Service代理k8s外部服务
4、使用Service反代理外部域名
5、Service常用类型

1、什么是Service

Service可以简单的理解为逻辑上的一组Pod。一种可以访问Pod的策略，而且其他Pod可以通过这个Service访问到这个Service代理的Pod。相对于Pod而言，它会有一个固定的名称，一旦创建就固定不变。

2、定义一个Service

创建Service文件

#查看 deploy
[root@k8s-master ~]# kubectl get deploy -owide
NAME    READY   UP-TO-DATE   AVAILABLE   AGE   CONTAINERS   IMAGES         SELECTOR
nginx   2/2     2            2           13h   nginx        nginx:1.21.6   app=nginx

查看pod
[root@k8s-master ~]# kubectl get po -owide
NAME                     READY   STATUS    RESTARTS       AGE    IP                NODE         NOMINATED NODE   READINESS GATES
busybox                  1/1     Running   50 (19m ago)   2d2h   192.161.125.10    k8s-node01              
nginx-6b5dc8646d-ph4d6   1/1     Running   0              135m   192.169.214.243   k8s-node03              
nginx-6b5dc8646d-w59mb   1/1     Running   0              13h    192.169.214.237   k8s-node03              


#创建文件
[root@k8s-master ~]# vim nginx-test-svc.yaml

apiVersion: v1
kind: Service
metadata:
  labels:
    app: nginx-test-svc
  name: nginx-test-svc
spec:
  ports:
  - name: http  #Service端口的名称
    port: 80 #Service自己的端口  如果是80端口 service-a 调用 service-b  http://service-b 不需要后面再写端口号
    protocol: TC P  #UDP TCP SCTP default：TCP
    targetPort: 80 #应用的端口
  - name: https
    port: 443
    protocol: TCP
    targetPort: 443
  selector:  #对应 deploy SELECTOR
    app: nginx
  sessionAffinity: None
  type: ClusterIP


[root@k8s-master ~]# kubectl create -f nginx-test-svc.yaml 
service/nginx-test-svc created


[root@k8s-master ~]# kubectl get svc
NAME             TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)          AGE
kubernetes       ClusterIP   10.96.0.1             443/TCP          12d
nginx-test-svc   ClusterIP   10.99.39.37           80/TCP,443/TCP   33s

#通过service ip 访问 nginx
[root@k8s-master ~]# curl 10.99.39.37



Welcome to nginx!

单独删除pod之后，并不影响svc的访问，因为pod所有的ip地址和端口号都会被记录到endpoint,endpoint在创建svc时自动创建，endpoint会动态的将svc跟pod结合起来

[root@k8s-master ~]# kubectl get ep
NAME             ENDPOINTS                                                                AGE
kubernetes       172.16.55.220:6443                                                       12d
nginx-test-svc   192.169.214.237:443,192.169.214.243:443,192.169.214.237:80 + 1 more...   109m


[root@k8s-master ~]# kubectl get ep nginx-test-svc -oyaml

apiVersion: v1
kind: Endpoints
metadata:
  annotations:
    endpoints.kubernetes.io/last-change-trigger-time: "2022-05-14T14:23:58Z"
  creationTimestamp: "2022-05-14T14:23:58Z"
  labels:
    app: nginx-test-svc
  name: nginx-test-svc
  namespace: default
  resourceVersion: "424732"
  uid: ff25d0e1-0889-4ca4-93c7-8c356c2cf0bd
subsets: 
- addresses: #动态的绑定pod
  - ip: 192.169.214.237
    nodeName: k8s-node03
    targetRef:
      kind: Pod
      name: nginx-6b5dc8646d-w59mb
      namespace: default
      resourceVersion: "335755"
      uid: 88e4d87b-b47a-4d80-88aa-a3fdb9278411
  - ip: 192.169.214.243
    nodeName: k8s-node03
    targetRef:
      kind: Pod
      name: nginx-6b5dc8646d-ph4d6
      namespace: default
      resourceVersion: "409688"
      uid: 7315d7d3-54a6-4348-adac-695024d73b40 
  ports:
  - name: https
    port: 443
    protocol: TCP
  - name: http
    port: 80
    protocol: TCP

3、使用Service代理k8s外部服务

希望在生产环境中使用某个固定的名称而非IP地址进行访问外部的中间件服务
希望Service指向另一个Namespace中或其他集群中的服务
某个项目正在迁移至k8s集群，但是一部分服务仍然在集群外部，此时可以使用service代理至k8s集群外部的服务

创建yaml文件

[root@k8s-master ~]# cp nginx-test-svc.yaml nginx-svc-external.yaml

#修改yaml
[root@k8s-master ~]# vim nginx-svc-external.yaml 

apiVersion: v1
kind: Service
metadata:
  labels:
    app: nginx-svc-external
  name: nginx-svc-external
spec:
  ports:
  - name: http  
    port: 80 
    protocol: TCP  
    targetPort: 80
  sessionAffinity: None
  type: ClusterIP

新建Service

[root@k8s-master ~]# kubectl create -f nginx-svc-external.yaml 
service/nginx-svc-external created

[root@k8s-master ~]# kubectl get svc
NAME                 TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
kubernetes           ClusterIP   10.96.0.1               443/TCP          12d
nginx-svc-external   ClusterIP   10.96.196.165           80/TCP           55s
nginx-test-svc       ClusterIP   10.99.39.37             80/TCP,443/TCP   163m

#没有对应的Endpoint 需要自己创建
[root@k8s-master ~]# kubectl get ep
NAME             ENDPOINTS                                                                AGE
kubernetes       172.16.55.220:6443                                                       12d
nginx-test-svc   192.169.214.237:443,192.169.214.243:443,192.169.214.237:80 + 1 more...   166m

#新建yaml
[root@k8s-master ~]# vim nginx-ep-external.yaml 

apiVersion: v1
kind: Endpoints
metadata:
  labels:
    app: nginx-svc-external  #名字要与svc 名称一致
  name: nginx-svc-external
  namespace: default
subsets:
- addresses:
  - ip: 172.16.55.201 #选择一个需要代理的IP
  ports:
  - name: http
    port: 80
    protocol: TCP

#创建Endpoint
[root@k8s-master ~]# kubectl create -f nginx-ep-external.yaml 
endpoints/nginx-svc-external created

[root@k8s-master ~]# kubectl get ep
NAME                 ENDPOINTS                                                                AGE
kubernetes           172.16.55.220:6443                                                       12d
nginx-svc-external   172.16.55.201:80                                                         9s
nginx-test-svc       192.169.214.237:443,192.169.214.243:443,192.169.214.237:80 + 1 more...   3h12m

[root@k8s-master ~]# kubectl get svc
NAME                 TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
kubernetes           ClusterIP   10.96.0.1               443/TCP          12d
nginx-svc-external   ClusterIP   10.96.196.165           80/TCP           36m
nginx-test-svc       ClusterIP   10.99.39.37             80/TCP,443/TCP   3h18m

#通过访问Service 地址 访问外部资源
[root@k8s-master ~]# curl 10.96.196.165 -I
HTTP/1.1 302 Found
Server: nginx
Date: Sat, 14 May 2022 17:43:03 GMT
Content-Type: text/html; charset=utf-8

#修改配置
[root@k8s-master ~]# kubectl edit ep nginx-svc-external
endpoints/nginx-svc-external edited

4、使用Service反代理外部域名

创建配置文件，反向代理百度

[root@k8s-master ~]# vim nginx-externalname.yaml

apiVersion: v1
kind: Service
metadata:
  labels:
    app: nginx-externalname
  name: nginx-externalname
spec:
  type: ExternalName
  externalName: www.baidu.com

#创建
[root@k8s-master ~]# kubectl create -f nginx-externalname.yaml 
service/nginx-externalname created

[root@k8s-master ~]# kubectl get svc
NAME                 TYPE           CLUSTER-IP      EXTERNAL-IP     PORT(S)          AGE
kubernetes           ClusterIP      10.96.0.1                 443/TCP          12d
nginx-externalname   ExternalName             www.baidu.com              45s
nginx-svc-external   ClusterIP      10.96.196.165             80/TCP           70m
nginx-test-svc       ClusterIP      10.99.39.37               80/TCP,443/TCP   3h52m

#进入 busybox 
[root@k8s-master ~]# kubectl exec -it busybox -- sh

#访问service 由于跨域 访问失败
/ # wget nginx-externalname
Connecting to nginx-externalname (104.193.88.77:80)
wget: server returned error: HTTP/1.1 500 Internal Server Error

#解析路由
/ # nslookup nginx-externalname
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      nginx-externalname
Address 1: 180.101.49.12
Address 2: 180.101.49.11

#访问最终地址
/ # wget 180.101.49.12
Connecting to 180.101.49.12 (180.101.49.12:80)
index.html           100% |***********************************************************************************************************************************************************************************************|  2381   0:00:00 ETA

5、Service常用类型

ClusterIP: 在集群内部使用，也是默认值
ExternalName:通过返回定义的CNAME别名
NodePort:在所有安装了kube-proxy的节点上打开一个端口，此端口可以代理至后端Pod，集群外部可以使用节点的IP地址和NodePort的端口号访问到集群的Pod的服务。NodePort 默认值是30000-32767
LoadBalancer:使用云提供商的负载均衡器公开服务

[root@k8s-master ~]# kubectl get svc -nkubernetes-dashboard
NAME                        TYPE        CLUSTER-IP     EXTERNAL-IP   PORT(S)         AGE
dashboard-metrics-scraper   ClusterIP   10.98.72.161           8000/TCP        12d
kubernetes-dashboard        NodePort    10.96.142.96           443:32628/TCP   12d

[root@k8s-master ~]# netstat -lntp | grep 32628
tcp        0      0 0.0.0.0:32628           0.0.0.0:*               LISTEN      1233/kube-proxy     

#修改NodePort 默认值是30000-32767
vim /usr/lib/systemd/system/kube-apiserver.service 

 --service-node-port-range=30000-32767

ClusterIP 改为 NodePort

#查看现有的svc
[root@k8s-master ~]# kubectl get svc
NAME                 TYPE           CLUSTER-IP      EXTERNAL-IP     PORT(S)          AGE
kubernetes           ClusterIP      10.96.0.1                 443/TCP          12d
nginx-externalname   ExternalName             www.baidu.com              8h
nginx-svc-external   ClusterIP      10.96.196.165             80/TCP           9h
nginx-test-svc       ClusterIP      10.99.39.37               80/TCP,443/TCP   12h


#修改配置
[root@k8s-master ~]# kubectl edit svc nginx-test-svc
service/nginx-test-svc edited

apiVersion: v1
kind: Service
metadata:
  creationTimestamp: "2022-05-14T14:23:58Z"
  labels:
    app: nginx-test-svc
  name: nginx-test-svc
  namespace: default
  resourceVersion: "424731"
  uid: 8ad8ff61-f6d6-4325-8573-bd2ca205ac0b
spec:
  clusterIP: 10.99.39.37
  clusterIPs:
  - 10.99.39.37
  internalTrafficPolicy: Cluster
  ipFamilies:
  - IPv4
  ipFamilyPolicy: SingleStack
  ports:
  - name: http
    port: 80
    protocol: TCP
    targetPort: 80
    nodePort: 31000 #自己指定端口号
  selector:
    app: nginx
  sessionAffinity: None
  type: NodePort #ClusterIP 改为 NodePort
status:
  loadBalancer: {}

#查看改完的svc
[root@k8s-master ~]# kubectl get svc
NAME                 TYPE           CLUSTER-IP      EXTERNAL-IP     PORT(S)        AGE
kubernetes           ClusterIP      10.96.0.1                 443/TCP        12d
nginx-externalname   ExternalName             www.baidu.com            8h
nginx-svc-external   ClusterIP      10.96.196.165             80/TCP         9h
nginx-test-svc       NodePort       10.99.39.37               80:31000/TCP   12h


#访问服务
[root@k8s-master ~]# curl http://172.16.55.220:31000/



Welcome to nginx!