企业项目实战k8s篇（五）service

一.service简述

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)

二.ipvs模式

• 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。

开启kube-proxy的ipvs模式

安装ipvs，修改ipvs模式

[[email protected] ~]# kubectl  -n kube-system  get cm
NAME                                 DATA   AGE
coredns                              1      2d23h
extension-apiserver-authentication   6      2d23h
kube-flannel-cfg                     2      2d22h
kube-proxy                           2      2d23h
kube-root-ca.crt                     1      2d23h
kubeadm-config                       2      2d23h
kubelet-config-1.21                  1      2d23h

[[email protected] ~]# kubectl edit cm kube-proxy -n kube-system
configmap/kube-proxy edited
[[email protected] ~]# lsmod  | grep ip_vs
ip_vs_sh               12688  0 
ip_vs_wrr              12697  0 
ip_vs_rr               12600  0 
ip_vs                 145497  6 ip_vs_rr,ip_vs_sh,ip_vs_wrr
nf_conntrack          133095  10 ip_vs,nf_nat,nf_nat_ipv4,nf_nat_ipv6,xt_conntrack,nf_nat_masquerade_ipv4,nf_nat_masquerade_ipv6,nf_conntrack_netlink,nf_conntrack_ipv4,nf_conntrack_ipv6
libcrc32c              12644  4 xfs,ip_vs,nf_nat,nf_conntrack

更新kube-proxy pod

[[email protected] ~]# kubectl get pod -n kube-system |grep kube-proxy |awk '{system("kubectl delete pod "$1" -n kube-system")}'
pod "kube-proxy-p78dh" deleted
pod "kube-proxy-rpqxv" deleted
pod "kube-proxy-tgvkq" deleted

执行脚本创建svc，获取访问ip 为10.96.97.61

[[email protected] ~]# kubectl  apply  -f deployment.yml 
deployment.apps/nginx-deployment configured
[[email protected] ~]# vim deployment.yml 
[[email protected] ~]# kubectl  get pod
NAME                                READY   STATUS    RESTARTS   AGE
nginx-deployment-6456d7c676-7zhl5   1/1     Running   0          32s
nginx-deployment-6456d7c676-ldq7x   1/1     Running   0          33s
nginx-deployment-6456d7c676-rlhkv   1/1     Running   0          35s
[[email protected] ~]# kubectl  apply  -f svc.yml 
service/mysvc created
[[email protected] ~]# kubectl  describe  svc mysvc 
Name:              mysvc
Namespace:         default
Labels:            <none>
Annotations:       <none>
Selector:          app=nginx
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                10.96.97.61
IPs:               10.96.97.61
Port:              <unset>  80/TCP
TargetPort:        80/TCP
Endpoints:         10.244.1.28:80,10.244.1.29:80,10.244.2.35:80
Session Affinity:  None
Events:            <none>

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

9: kube-ipvs0: <BROADCAST,NOARP> mtu 1500 qdisc noop state DOWN group default 
    link/ether 2a:78:08:d8:21:10 brd ff:ff:ff:ff:ff:ff
 
    inet 10.96.97.61/32 scope global kube-ipvs0
       valid_lft forever preferred_lft forever

kube-proxy通过linux的IPVS模块,以rr轮询方式调度service中的Pod，进行转发访问，从而减少性能消耗

[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# curl 10.96.97.61
Hello MyApp | Version: v1 | <a href="hostname.html">Pod Name</a>
[[email protected] ~]# ipvsadm -ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn   
TCP  10.96.97.61:80 rr
  -> 10.244.1.28:80               Masq    1      0          3         
  -> 10.244.1.29:80               Masq    1      0          4         
  -> 10.244.2.35:80               Masq    1      0          4