两种非凡类型的svc
Headless Service
- Headless Service
有时不须要或不想要负载平衡，以及独自的 Service IP 。遇到这种状况，能够通过指定 Cluster IP(spec.clusterIP) 的值为 “None” 来创立 Headless Service 。这类 Service 并不会调配 Cluster IP， kube-
proxy 不会解决它们，而且平台也不会为它们进行负载平衡和路由每个个体都具备肯定水平的独特性，由其存储的状态决定;
Headless Services是一种非凡的service，其spec:clusterIP示意为None，这样在理论运行时就不会被调配ClusterIP。也被称为无头服务。 - headless Service和一般Service的区别
headless不调配clusterIP
headless service能够通过解析service的DNS，返回所有Pod的地址和DNS(statefulSet部署的Pod才有DNS) 一般的service，只能通过解析service的DNS返回service的ClusterIP - statefulSet和Deployment控制器的区别
statefulSet下的Pod有DNS地址,通过解析Pod的DNS能够返回Pod的IP
deployment下的Pod没有DNS - 一般Service解析service的DNS后果
- headless Service 就是没头的Service,有什么应用场景呢?
第一种: 自主选择权,有时候client想本人决定应用哪个Real Server,能够通过查问DNS来获取Real Server的信息
第二种: headless service关联的每个endpoint(也就是Pod),都会有对应的DNS域名;这样Pod之间就能够相互拜访 - headless service个别和statefulSet联合应用
为什么要用headless service+statefulSet部署有状态利用?
- headless service会为关联的Pod调配一个域
<service name>.$<namespace name>.svc.cluster.local - StatefulSet会为关联的Pod放弃一个不变的Pod Name
statefulset中Pod的hostname格局为$(StatefulSet name)-$(pod序号) - StatefulSet会为关联的Pod调配一个dnsName
$<Pod Name>.$<service name>.$<namespace name>.svc.cluster.local
示例1.Headless Service无头服务解析
[root@k8s-master svc]# cat demoapp-headless-svc.yaml
apiVersion: v1
kind: Service
metadata:
name: demoapp-headless-svc
spec:
clusterIP: None #必须为None
selector:
app: demoapp
ports:
- port: 80
targetPort: 80
name: http
[root@k8s-master centos]# kubectl exec centos-deployment-66d8cd5f8b-nrfnv -it -- /bin/bash
root@centos-deployment-66d8cd5f8b-nrfnv /]# nslookup -query=A demoapp-headless-svc #解析到是后端pod IP
Server: 10.96.0.10
Address: 10.96.0.10#53
Name: demoapp-headless-svc.default.svc.cluster.local
Address: 10.244.1.103
Name: demoapp-headless-svc.default.svc.cluster.local
Address: 10.244.2.99
Name: demoapp-headless-svc.default.svc.cluster.local
Address: 10.244.2.97
Name: demoapp-headless-svc.default.svc.cluster.local
Address: 10.244.1.102
[root@centos-deployment-66d8cd5f8b-nrfnv /]# nslookup -query=PTR 10.244.1.103 #对pod IP进行反解 失去所有绑定的SVC
Server: 10.96.0.10
Address: 10.96.0.10#53
103.1.244.10.in-addr.arpa name = 10-244-1-103.demoapp-svc.default.svc.cluster.local.
103.1.244.10.in-addr.arpa name = 10-244-1-103.demoapp-nodeport-svc.default.svc.cluster.local.
103.1.244.10.in-addr.arpa name = 10-244-1-103.demoapp-loadbalancer-svc.default.svc.cluster.local.
103.1.244.10.in-addr.arpa name = 10-244-1-103.demoapp-externalip-svc.default.svc.cluster.local.
103.1.244.10.in-addr.arpa name = 10-244-1-103.demoapp-headless-svc.default.svc.cluster.local.
[root@centos-deployment-66d8cd5f8b-nrfnv /]# curl 10.244.1.103
iKubernetes demoapp v1.0 !! ClientIP: 10.244.1.104, ServerName: demoapp-66db74fcfc-2jf49, ServerIP: 10.244.1.103!
[root@centos-deployment-66d8cd5f8b-nrfnv /]#
[root@centos-deployment-66d8cd5f8b-nrfnv /]#
[root@centos-deployment-66d8cd5f8b-nrfnv /]# curl demoapp-headless-svc #须要留神的是Headless Service只有集群外部能拜访，宿主机上因为无奈解析到SVC IP是拜访的
iKubernetes demoapp v1.0 !! ClientIP: 10.244.1.104, ServerName: demoapp-66db74fcfc-5dp5n, ServerIP: 10.244.1.102!
[root@centos-deployment-66d8cd5f8b-nrfnv /]# curl demoapp-headless-svc
iKubernetes demoapp v1.0 !! ClientIP: 10.244.1.104, ServerName: demoapp-66db74fcfc-z682r, ServerIP: 10.244.2.99!
[root@centos-deployment-66d8cd5f8b-nrfnv /]# curl demoapp-headless-svc
iKubernetes demoapp v1.0 !! ClientIP: 10.244.1.104, ServerName: demoapp-66db74fcfc-9wkgj, ServerIP: 10.244.2.97!
[root@centos-deployment-66d8cd5f8b-nrfnv /]# exit
[root@k8s-master svc]# curl demoapp-headless-svc #无法访问
curl: (6) Could not resolve host: demoapp-headless-svc; Unknown error
Service类型中的第四种:ExternalName
externalName Service是k8s中一个非凡的service类型，它不须要指定selector去抉择哪些pods实例提供服务，而是应用DNS CNAME机制把本人CNAME到你指定的另外一个域名上，你能够提供集群内的名字，比方mysql.db.svc这样的建设在db命名空间内的mysql服务，也能够指定http://mysql.example.com这样的内部实在域名。
CNAME是很有用的一个性能，在不同的域名之间搭建桥梁达到明一个域名暗另一个域名，比方github就通过CNAME机制来达到为用户提供公有域名站点的性能，云服务商也都是应用CNAME为用户提供各种各样的服务。作为明域名的所有者，我能够用A云来提供服务，哪天我口味变了，我换成B云提供服务，对我的用户的来说没有任何感知。
示例2：www.baidu.com cname到svc
[root@k8s-master svc]# cat externalname-redis-svc.yaml
apiVersion: v1
kind: Service
metadata:
name: externalname-http-svc
namespace: default
spec:
type: ExternalName
externalName: www.baidu.com
ports:
- protocol: TCP
port: 80
targetPort: 80
selector: {}
[root@k8s-master svc]# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
demoapp-deploy ClusterIP 10.109.159.225 <none> 80/TCP 3d3h
externalname-http-svc ExternalName <none> www.baidu.com 80/TCP 87m
#新增Pod测试
[root@k8s-master storage]# kubectl run pod-$RANDOM --image=ikubernetes/admin-box:latest -it --rm --command -- /bin/sh
root@pod-7813 # nslookup -query=A externalname-http-svc
Server: 10.96.0.10
Address: 10.96.0.10#53
externalname-http-svc.default.svc.cluster.local canonical name = www.baidu.com.
www.baidu.com canonical name = www.a.shifen.com.
Name: www.a.shifen.com
Address: 180.101.49.11
Name: www.a.shifen.com
Address: 180.101.49.12
root@pod-7813 # curl -H "host:www.baidu.com" externalname-http-svc.default.svc.cluster.local
<!DOCTYPE html>
<!--STATUS OK--><html> <head><meta http-equiv=content-type content=text/html;charset=utf-8><meta http-equiv=X-UA-Compatible content=IE=Edge><meta content=always name=referrer><link rel=stylesheet type=text/css href=http://s1.bdstatic.com/r/www/cache/bdorz/baidu.min.css><title>百度一下，你就晓得
....
root@pod-7813 # 参考链接:
https://zhuanlan.zhihu.com/p/…
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