Service
说明:
Service 是作用于客户端可服务端(Pod)之间，作为一个固定的中间层
主要依赖于kubernetes中的DNS服务，1.11版本之前用的是kube-dns
而之后的版本使用的CoreDNS服务。
在kubernetes中有三种网络：
1. node network
2. pod network
3. cluster network (service network/virtual IP) 集群IP/虚拟IP
kube-proxy通过watch监视api service 有关Service的变动
kubernetes有三种工作模式：
1. userspace 1.1 之前
2. iptables 1.10 之前
3. ipvs 1.11 之后
Service 类型
ExternalName # 关联集群外部的一个服务，用于集群内部有需求访问的资源通过Service去访问。
ClusterIP # 默认，配置一个集群IP，仅用于集群内部使用
NodePort # 集群外部
LoadBalancer # 把集群环境部署在云环境中，而云环境也支持LB
ClusterIP
有头 Service
手动创建清单文件
[root@master manifests]# cat svc-redis.yaml
apiVersion: v1
kind: Service # 指定类型
metadata:
name: redis
namespace: default
spec:
selector: # 标签选择器
app: redis
role: logstor
clusterIP: 10.97.97.97 # 这里的clusterIP 可以手动指定IP，如果不指定，则会自动获取一个IP
type: ClusterIP
ports:
- port: 6379 # 这里的端口表示Service暴露的端口
targetPort: 6379 # 这里表示匹配到的Pod 端口
创建
[root@master manifests]# kubectl apply -f svc-redis.yaml
service/redis created
[root@master manifests]# kubectl get svc -o wide
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 15d <none>
redis ClusterIP 10.97.97.97 <none> 6379/TCP 5s app=redis,role=logstor # 这里可以看出已经匹配到了对应的Pod
[root@master manifests]# kubectl describe svc redis
Name: redis
Namespace: default
Labels: <none>
Annotations: kubectl.kubernetes.io/last-applied-configuration:
{"apiVersion":"v1","kind":"Service","metadata":{"annotations":{},"name":"redis","namespace":"default"},"spec":{"clusterIP":"10.97.97.97","...
Selector: app=redis,role=logstor
Type: ClusterIP
IP: 10.97.97.97
Port: <unset> 6379/TCP
TargetPort: 6379/TCP
Endpoints: 10.244.1.24:6379
Session Affinity: None
Events: <none>
[root@master manifests]# kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
myapp-ds-8tvmc 1/1 Running 0 5h34m 10.244.1.25 node03.kubernetes <none> <none>
myapp-ds-cs2hw 1/1 Running 0 5h33m 10.244.3.27 node01.kubernetes <none> <none>
myapp-ds-f2pp8 1/1 Running 0 5h34m 10.244.2.20 node02.kubernetes <none> <none>
redis-5c998b644f-wnzrd 1/1 Running 0 5h59m 10.244.1.24 node03.kubernetes <none> <none> # 这里redis的Pod 和刚刚创建svc匹配的Pod的IP地址相同
资源记录:
SVC_NAME.NSNAME.DEMAIN.LTD.
svc.cluster.local.
手动测试集群内创建的DNS解析:
按照上面的记录，资源解析记录为: redis.default.svc.cluster.local.
进入到其中一台Pod中尝试解析:
[root@master manifests]# kubectl exec -it myapp-ds-8tvmc -- /bin/sh
/ # nslookup redis.default.svc.cluster.local.
nslookup: can't resolve '(null)': Name does not resolve
Name: redis.default.svc.cluster.local.
Address 1: 10.97.97.97 redis.default.svc.cluster.local
无头 Service
与有头Service区别是 ClusterIP 为空，而解析到的Service 直接是后端的Pod的IP地址
[root@master manifests]# cat myapp-svc-headless.yaml
apiVersion: v1
kind: Service
metadata:
name: myapp-svc
namespace: default
spec:
selector:
app: myapp
release: canary
clusterIP: "None" # 这里为None
ports:
- port: 80
targetPort: 80
[root@master manifests]# kubectl apply -f myapp-svc-headless.yaml
service/myapp-svc created
[root@master manifests]# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 16d
myapp NodePort 10.99.99.99 <none> 80:30080/TCP 17h
myapp-svc ClusterIP None <none> 80/TCP 3s
redis ClusterIP 10.97.97.97 <none> 6379/TCP 18h
下面手动解析测试：
[root@master manifests]# dig -t A myapp-svc.default.svc.cluster.local. @10.96.0.10
; <<>> DiG 9.9.4-RedHat-9.9.4-74.el7_6.1 <<>> -t A myapp-svc.default.svc.cluster.local. @10.96.0.10
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 52484
;; flags: qr aa rd; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;myapp-svc.default.svc.cluster.local. IN A
;; ANSWER SECTION:
myapp-svc.default.svc.cluster.local. 30 IN A 10.244.1.20
myapp-svc.default.svc.cluster.local. 30 IN A 10.244.3.23
myapp-svc.default.svc.cluster.local. 30 IN A 10.244.3.22 # 这里解析的是匹配到的后端的Pod地址
myapp-svc.default.svc.cluster.local. 30 IN A 10.244.2.16
myapp-svc.default.svc.cluster.local. 30 IN A 10.244.2.15
;; Query time: 1 msec
;; SERVER: 10.96.0.10#53(10.96.0.10)
;; WHEN: Fri Jul 26 10:04:24 CST 2019
;; MSG SIZE rcvd: 319
[root@master manifests]# kubectl get pods -o wide -l app=myapp
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
myapp-deploy-f4db5d79c-7hnfg 1/1 Running 0 46h 10.244.2.16 node02.kubernetes <none> <none>
myapp-deploy-f4db5d79c-85hpm 1/1 Running 0 46h 10.244.3.22 node01.kubernetes <none> <none>
myapp-deploy-f4db5d79c-b9h4s 1/1 Running 0 46h 10.244.2.15 node02.kubernetes <none> <none>
myapp-deploy-f4db5d79c-tm9mt 1/1 Running 0 46h 10.244.1.20 node03.kubernetes <none> <none>
myapp-deploy-f4db5d79c-xp8t6 1/1 Running 0 46h 10.244.3.23 node01.kubernetes <none> <none>
而解析有头的Service 则是Service自己的地址：
[root@master manifests]# dig -t A myapp.default.svc.cluster.local. @10.96.0.10
; <<>> DiG 9.9.4-RedHat-9.9.4-74.el7_6.1 <<>> -t A myapp.default.svc.cluster.local. @10.96.0.10
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14743
;; flags: qr aa rd; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;myapp.default.svc.cluster.local. IN A
;; ANSWER SECTION:
myapp.default.svc.cluster.local. 30 IN A 10.99.99.99
;; Query time: 0 msec
;; SERVER: 10.96.0.10#53(10.96.0.10)
;; WHEN: Fri Jul 26 10:05:33 CST 2019
;; MSG SIZE rcvd: 107