面试腾讯高级开发岗被问：k8s之Service详解-Service使用
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实验环境准备
在使用service之前，首先利用deployment创建出3个pod，注意要为pod设置app=nginx-pod的标签
创建deployment.yaml，内容如下
apiVersion: apps/v1
kind: Deployment
metadata:
name: pc-deployment
namespace: dev
spec:
replicas: 3
selector:
matchLabels:
app: nginx-pod
template:
metadata:
labels:
app: nginx-pod
spec:
containers:
- name: nginx
image: nginx:1.17.1
ports:
- containerPort: 80
使用配置文件
[root@master ~]# vim deployment.yaml
[root@master ~]# kubectl create -f deployment.yaml
deployment.apps/pc-deployment created
[root@master ~]# kubectl get pod -n dev -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
pc-deployment-6696798b78-5d7rh 1/1 Running 0 4s 10.244.2.4 node2 <none> <none>
pc-deployment-6696798b78-5jbcr 1/1 Running 0 4s 10.244.1.26 node1 <none> <none>
pc-deployment-6696798b78-wbrfh 1/1 Running 0 4s 10.244.2.3 node2 <none> <none>
通过pod的Ip加上容器端口80访问nginx，发现可以访问
[root@master ~]# curl 10.244.2.4:80
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
为了方便后面的测试，修改下面三台nginx的index.html页面（三台修改的Ip地址不一致）
#修改第一个pod
[root@master ~]# kubectl exec -it pc-deployment-6696798b78-5d7rh -n dev /bin/sh
# echo "10.244.2.4" > /usr/share/nginx/html/index.html
# exit
#测试访问
[root@master ~]# curl 10.244.2.4:80
10.244.2.4
#修改第二个pod
[root@master ~]# kubectl exec -it pc-deployment-6696798b78-5jbcr -n dev /bin/sh
# echo "10.244.1.26" > /usr/share/nginx/html/index.html
# exit
#修改第三个pod
[root@master ~]# kubectl exec -it pc-deployment-6696798b78-wbrfh -n dev /bin/sh
# echo "10.244.2.3" > /usr/share/nginx/html/index.html
# exit
ClusterIp类型的Service
创建service-clusterip.yaml文件
apiVersion: v1
kind: Service
metadata:
name: service-clusterip
namespace: dev
spec:
selector:
app: nginx-pod
clusterIP: 10.97.97.97 #service的Ip地址，如果不写，会默认生成一个
type: ClusterIP
ports:
- port: 80 #service端口
targetPort: 80 #pod端口
使用配置文件
[root@master ~]# vim service-clusterip.yaml
[root@master ~]# kubectl create -f service-clusterip.yaml
service/service-clusterip created
[root@master ~]# kubectl get svc service-clusterip -n dev
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service-clusterip ClusterIP 10.97.97.97 <none> 80/TCP 44s
#查看service详细信息
[root@master ~]# kubectl describe svc service-clusterip -n dev
Name: service-clusterip
Namespace: dev
Labels: <none>
Annotations: <none>
Selector: app=nginx-pod
Type: ClusterIP
IP: 10.97.97.97
Port: <unset> 80/TCP
TargetPort: 80/TCP
Endpoints: 10.244.1.26:80,10.244.2.3:80,10.244.2.4:80
Session Affinity: None
Events: <none>
#查看ipvs映射规则
[root@master ~]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 10.97.97.97:80 rr
-> 10.244.1.27:80 Masq 1 0 0
-> 10.244.2.5:80 Masq 1 0 0
-> 10.244.2.6:80 Masq 1 0 0
EndPoint
Endpoint是k8s中的一个资源对象，存储在etcd中，用来记录一个service对应的所有pod的访问地址，它是根据service配置文件中的selector描述产生的
一个service由一组pod组成，这些pod通过endpoints暴露出来，endpoints是实现实际服务的端点集合。换句话说，service和pod之间的联系是通过endpoints实现的。
[root@master ~]# kubectl get endpoints -n dev -o wide
NAME ENDPOINTS AGE
service-clusterip 10.244.1.26:80,10.244.2.3:80,10.244.2.4:80 18m
负载分发策略
对service的访问被分发到了后端的pod上去，目前k8s提供了两种负载分发策略：
- 如果不定义，默认使用kube-proxy的策略，比如随机，轮询
- 基于客户端地址的会话保持模式，即来自同一个客户端发起的所有请求都会转发到一个固定的pod上，此模式可以使在spec中添加sessionAffinity:ClientIP选项
#查看ipvs映射规则
[root@master ~]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 10.97.97.97:80 rr
-> 10.244.1.27:80 Masq 1 0 0
-> 10.244.2.5:80 Masq 1 0 0
-> 10.244.2.6:80 Masq 1 0 0
#循环访问测试
[root@master ~]# while true;do curl 10.97.97.97:80;sleep 5;done;
10.244.1.26
10.244.2.3
10.244.2.4
10.244.1.26
10.244.2.3
10.244.2.4
10.244.1.26
10.244.2.3
10.244.2.4
修改分发策略为sessionAffinity:ClientIP
#删除原来的service
[root@master ~]# kubectl delete -f service-clusterip.yaml
service "service-clusterip" deleted
#更改service-clusterip.yaml
[root@master ~]# vim service-clusterip.yaml
apiVersion: v1
kind: Service
metadata:
name: service-clusterip
namespace: dev
spec:
sessionAffinity: ClientIP
selector:
app: nginx-pod
clusterIP: 10.97.97.97 #service的Ip地址，如果不写，会默认生成一个
type: ClusterIP
ports:
- port: 80 #service端口
targetPort: 80 #pod端口
#重建service
[root@master ~]# kubectl create -f service-clusterip.yaml
service/service-clusterip created
#查看svc，可以发现新增了一项SessionAffinity
[root@master ~]# kubectl describe svc service-clusterip -n dev
Name: service-clusterip
Namespace: dev
Labels: <none>
Annotations: <none>
Selector: app=nginx-pod
Type: ClusterIP
IP: 10.97.97.97
Port: <unset> 80/TCP
TargetPort: 80/TCP
Endpoints: 10.244.1.27:80,10.244.2.5:80,10.244.2.6:80
Session Affinity: ClientIP
Events: <none>
重新查看ipvs映射规则【persistent代表持久】，发现新增了persistent 10800秒，代表持续180分钟
[root@master ~]# ipvsadm -Ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port Forward Weight ActiveConn InActConn
TCP 10.97.97.97:80 rr persistent 10800
-> 10.244.1.27:80 Masq 1 0 0
-> 10.244.2.5:80 Masq 1 0 0
-> 10.244.2.6:80 Masq 1 0 0
再次进行循环访问测试，发现这次只访问一个pod
[root@master ~]# while true;do curl 10.97.97.97:80;sleep 5;done;
10.244.2.4
10.244.2.4
10.244.2.4
10.244.2.4
10.244.2.4
10.244.2.4
HeadLiness类型的Service
在某些场景中，开发人员可能不想使用Service提供的负载均衡功能，而希望自己来控制负载均衡策略，针对这种情况，k8s提供了HeadLiness Service，这类Service不会分配ClusterIP，如果想要访问Service，只能通过service的域名进行查询。
创建service-headliness.yaml
apiVersion: v1
kind: Service
metadata:
name: service-headliness
namespace: dev
spec:
selector:
app: nginx-pod
clusterIP: None #将clusterIP设置为None，即可创建headliness Service
type: ClusterIP
ports:
- port: 80
targetPort: 80
使用配置文件
[root@master ~]# vim service-headliness.yaml
[root@master ~]# kubectl create -f service-headliness.yaml
service/service-headliness created
[root@master ~]# kubectl get svc service-headliness -n dev
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service-headliness ClusterIP None <none> 80/TCP 31s
[root@master ~]# kubectl describe svc service-headliness -n dev
Name: service-headliness
Namespace: dev
Labels: <none>
Annotations: <none>
Selector: app=nginx-pod
Type: ClusterIP
IP: None
Port: <unset> 80/TCP
TargetPort: 80/TCP
Endpoints: 10.244.1.27:80,10.244.2.5:80,10.244.2.6:80
Session Affinity: None
Events: <none>
查看域名解析情况
[root@master ~]# kubectl exec -it pc-deployment-6696798b78-5d7rh -n dev /bin/sh
# cat /etc/resolv.conf
nameserver 10.96.0.10
search dev.svc.cluster.local svc.cluster.local cluster.local
options ndots:5
# exit
#通过域名进行查询
[root@master ~]# dig @10.96.0.10 service-headliness.dev.svc.cluster.local
; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.el7_9.5 <<>> @10.96.0.10 service-headliness.dev.svc.cluster.local
; (1 server found)
;; 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: 40115
;; 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:
;service-headliness.dev.svc.cluster.local. IN A
;; ANSWER SECTION:
service-headliness.dev.svc.cluster.local. 30 IN A 10.244.2.6
service-headliness.dev.svc.cluster.local. 30 IN A 10.244.1.27
service-headliness.dev.svc.cluster.local. 30 IN A 10.244.2.5
;; Query time: 334 msec
;; SERVER: 10.96.0.10#53(10.96.0.10)
;; WHEN: 四 8月 12 11:26:01 CST 2021
;; MSG SIZE rcvd: 237
NodePort类型的Service
在之前的样例中，创建的Service的IP地址只有集群内部可以访问，如果希望Service暴露给集群外部使用，那么就要使用到另外一种类型的Service，称为NodePort类型。NodePor的工作原理其实就是将service的端口映射到Node的一个端口上，然后就可以通过NodeIp:NodePort来访问service了。
创建service-nodeport.yaml，内容如下
apiVersion: v1
kind: Service
metadata:
name: service-nodeport
namespace: dev
spec:
selector:
app: nginx-pod
type: NodePort #service类型
ports:
- port: 80
nodePort: 30002 #指定绑定的node的端口（默认的取值范围是：30000-32767），如果不指定，会默认分配
targetPort: 80
使用配置文件
[root@master ~]# vim service-nodeport.yaml
[root@master ~]# kubectl create -f service-nodeport.yaml
service/service-nodeport created
[root@master ~]# kubectl get svc service-nodeport -n dev
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service-nodeport NodePort 10.103.29.82 <none> 80:30002/TCP 14s
通过电脑的浏览器对node进行访问，访问地址：master的主机ip加上30002端口
发现能够成功访问了
LoadBalancer类型的Service
LoadBalancer和NodePort很相似，目的都是向外部暴露一个端口，区别在于LoadBalancer会在集群的外部再来做一个负载均衡设备，而这个设备需要外部环境支持的，外部服务发送到这个设备上的请求，会被设备负载之后转发到集群中。
ExternalName类型的Service
ExternalName类型的Service用于引入集群外部的服务，它通过externalName属性指定外部一个服务的地址，然后在集群内部访问此Service就可以访问到外部的服务了
创建service-externalname.yaml，内容如下
apiVersion: v1
kind: Service
metadata:
name: service-externalname
namespace: dev
spec:
type: ExternalName #service类型
externalName: www.baidu.com #改成ip地址也可以
使用配置文件
[root@master ~]# vim service-externalname.yaml
[root@master ~]# kubectl create -f service-externalname.yaml
service/service-externalname created
[root@master ~]# kubectl get svc service-externalname -n dev
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service-externalname ExternalName <none> www.baidu.com <none> 17s
域名解析
[root@master ~]# dig @10.96.0.10 service-externalname.dev.svc.cluster.local
; <<>> DiG 9.11.4-P2-RedHat-9.11.4-26.P2.el7_9.5 <<>> @10.96.0.10 service-externalname.dev.svc.cluster.local
; (1 server found)
;; 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: 27636
;; flags: qr aa rd; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;service-externalname.dev.svc.cluster.local. IN A
;; ANSWER SECTION:
service-externalname.dev.svc.cluster.local. 30 IN CNAME www.baidu.com.
www.baidu.com. 30 IN CNAME www.a.shifen.com.
www.a.shifen.com. 30 IN A 39.156.66.14
www.a.shifen.com. 30 IN A 39.156.66.18
;; Query time: 31 msec
;; SERVER: 10.96.0.10#53(10.96.0.10)
;; WHEN: 四 8月 12 11:58:31 CST 2021
;; MSG SIZE rcvd: 247
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