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暴露服务,以便可以访问,动态负载均衡,(容器环境,ip地址动态,)
Service可以看作是一组提供相同服务的Pod对外的访问接口。借助Service,应用可以方便地实现服务发现和负载均衡。
service默认只支持4层负载均衡能力,没有7层功能。(可以通过Ingress实现)
service的类型:
ClusterIP:默认值,k8s系统给service自动分配的虚拟IP,只能在集群内部访问。
NodePort:将Service通过指定的Node上的端口暴露给外部,访问任意一个NodeIP:nodePort都将路由到ClusterIP。
LoadBalancer:在 NodePort 的基础上,借助 cloud provider 创建一个外部的负载均衡器,并将请求转发到 :NodePort,此模式只能在云服务器上使用。
ExternalName:将服务通过 DNS CNAME 记录方式转发到指定的域名(通过 spec.externlName 设定)。集群内部访问外部
联系之前的docker-Proxy学习
Service 是由 kube-proxy 组件,加上 iptables 来共同实现的.
kube-proxy 通过 iptables 处理 Service 的过程,需要在宿主机上设置相当多的 iptables 规则,如果宿主机有大量的Pod,不断刷新iptables规则,会消耗大量的CPU资源。
IPVS模式
的service,可以使K8s集群支持更多量级的Pod。
实验环境
[root@server2 ~]# kubectl apply -f rs.yml deployment.apps/deployment created [root@server2 ~]# cat rs.yml apiVersion: apps/v1 kind: Deployment metadata: name: deployment spec: replicas: 3 selector: matchLabels: app: nginx template: metadata: labels: app: nginx spec: containers: - name: nginx image: myapp:v1 [root@server2 ~]# kubectl expose deployment deployment --port=80 service/deployment exposed [root@server2 ~]# kubectl get svc NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE deployment ClusterIP 10.104.98.119 <none> 80/TCP 7s kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 9d [root@server2 ~]# kubectl describe svc deployment Name: deployment Namespace: default Labels: <none> Annotations: <none> Selector: app=nginx Type: ClusterIP IP Families: <none> IP: 10.104.98.119 IPs: 10.104.98.119 Port: <unset> 80/TCP TargetPort: 80/TCP Endpoints: 10.244.1.71:80,10.244.1.72:80,10.244.1.73:80 Session Affinity: None Events: <none>
通过iptables规则
[root@server2 ~]# iptables -t nat -nL | grep :80
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 /* default/deployment */ tcp to:10.244.1.71:80
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 /* default/deployment */ tcp to:10.244.1.72:80
DNAT tcp -- 0.0.0.0/0 0.0.0.0/0 /* default/deployment */ tcp to:10.244.1.73:80
KUBE-MARK-MASQ tcp -- !10.244.0.0/16 10.104.98.119 /* default/deployment cluster IP */ tcp dpt:80
KUBE-SVC-ZBZTQJVIH62KRRHU tcp -- 0.0.0.0/0 10.104.98.119 /* default/deployment cluster IP */ tcp dpt:80
[root@server2 ~]#
yum install -y ipvsadm
//所有节点安装
kubectl edit cm kube-proxy -n kube-system
//修改IPVS模式 服务的配置从镜像中独立出来
mode: "ipvs"
kubectl get pod -n kube-system |grep kube-proxy | awk '{system("kubectl delete pod "$1" -n kube-system")}'
//更新kube-proxy pod
可以观察到建立的副本数,当文件里面 的副本数发生改变的时候,可以直接在此处观察到,lvs负载均衡器
kube-proxy通过linux的IPVS模块,以rr轮询方式调度service中的Pod
ipvs模式负载均衡
[root@server2 ~]# curl 10.104.98.119
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[root@server2 ~]# curl 10.104.98.119/hostname.html
deployment-6456d7c676-qnnw5
[root@server2 ~]# curl 10.104.98.119/hostname.html
deployment-6456d7c676-svkdn
[root@server2 ~]# curl 10.104.98.119/hostname.html
deployment-6456d7c676-68hlt
[root@server2 ~]# curl 10.104.98.119/hostname.html
deployment-6456d7c676-qnnw5
IPVS模式下,kube-proxy会在service创建后,在宿主机上添加一个虚拟网卡:kube-ipvs0,
并分配service IP。
每个节点都有
当继续添加时
[root@server2 ~]# cat demo.yml --- apiVersion: v1 kind: Service metadata: name: myservice spec: selector: app: myapp ports: - protocol: TCP port: 80 targetPort: 80 --- apiVersion: apps/v1 kind: Deployment metadata: name: demo2 spec: replicas: 3 selector: matchLabels: app: myapp template: metadata: labels: app: myapp spec: containers: - name: myapp image: myapp:v2
为整个集群提供dns解析
Headless Service不需要分配一个VIP
,而是直接以DNS记录的方式解析
出被代理Pod的IP地址。
域名格式:$(servicename).$(namespace).svc.cluster.local
[root@server2 ~]# cat demo.yml --- apiVersion: v1 kind: Service metadata: name: myservice spec: selector: app: myapp ports: - protocol: TCP port: 80 targetPort: 80 clusterIP: None #不给ip地址 --- apiVersion: apps/v1 kind: Deployment metadata: name: demo2 spec: replicas: 3 selector: matchLabels: app: myapp template: metadata: labels: app: myapp spec: containers: - name: myapp image: myapp:v2 [root@server2 ~]# kubectl apply -f demo.yml
每个pod有相应的A记录解析
/ # curl 10.244.1.83 10-244-1-83.myservice.default.svc.cluster.local/hostname.html
Hello MyApp | Version: v2 | <a href="hostname.html">Pod Name</a>
demo2-67f8c948cf-tnjs9
Pod滚动更新后,依然可以解析:
$ kubectl delete pod --all
pod "deployment-nginx-58f549b56d-4qswl" deleted
pod "deployment-nginx-58f549b56d-7sz7c" deleted
pod "deployment-nginx-58f549b56d-gwswr" deleted
$ dig -t A nginx-svc.default.svc.cluster.local @10.96.0.10
...
;; QUESTION SECTION:
;nginx-svc.default.svc.cluster.local. IN A
;; ANSWER SECTION:
nginx-svc.default.svc.cluster.local. 30 IN A 10.244.2.111
nginx-svc.default.svc.cluster.local. 30 IN A 10.244.1.120
nginx-svc.default.svc.cluster.local. 30 IN A 10.244.0.61
在nodeport基础上分一个ip
从外部访问 Service 的第二种方式,适用于公有云上的 Kubernetes 服务。这时候,你可以指定一个 LoadBalancer 类型的 Service。
$ vim lb-service.yaml
apiVersion: v1
kind: Service
metadata:
name: lb-nginx
spec:
ports:
- name: http
port: 80
targetPort: 80
selector:
app: nginx
type: LoadBalancer
在service提交后,Kubernetes就会调用 CloudProvider 在公有云上为你创建一个负载均衡服务,并且把被代理的 Pod 的 IP地址配置给负载均衡服务做后端。
[root@server2 ~]# cat demo.yml --- apiVersion: v1 kind: Service metadata: name: myservice spec: selector: app: myapp ports: - protocol: TCP port: 80 targetPort: 80 #clusterIP: None #不给ip地址 #type: NodePort #type: LoadBalancer externalIPs: - 172.25.10.100 ###分配一个共有ip --- apiVersion: apps/v1 kind: Deployment metadata: name: demo2 spec: replicas: 3 selector: matchLabels: app: myapp template: metadata: labels: app: myapp spec: containers: - name: myapp image: myapp:v2
通过公有地址可以直接访问
集群外部资源发生改变时,直接修改文件里面的域名
www.westos.org 西开官网
$ vim ex-service.yaml
apiVersion: v1
kind: Service
metadata:
name: my-service
spec:
type: ExternalName
externalName: wwwwestos.org
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