一、Service概念
通過創建service可以爲一組具有相同功能的容器應用提供一個統一的入口地址，並將請求負載分發到後端的各個容器應用上。
二、Service基本用法
1.定義一個web服務的RC，由兩個tomcat容器副本組成
# cat webapp-rc.yaml
apiVersion: v1
kind: ReplicationController
metadata:
name: webapp
spec:
replicas: 2
template:
metadata:
name: webapp
labels:
app: webapp
spec:
containers:
- name: webapp
image: tomcat
ports:
- containerPort: 80802.創建該RC
# kubectl get pod
NAME READY STATUS RESTARTS AGE
webapp-t5q4g 1/1 Running 0 17m
webapp-wq88m 1/1 Running 0 17m
# kubectl get pods -l app=webapp -o yaml | grep podIP
podIP: 10.44.0.2
podIP: 10.36.0.1
3.使用kubectl expose創建一個SVC
# kubectl expose rc webapp
service/webapp exposed# kubectl get svc
webapp ClusterIP 10.111.192.152 <none> 8080/TCP 8s
4.通過svc地址和端口訪問
# curl 10.111.192.152:8080
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>Apache Tomcat/8.5.42</title>
......對svc地址10.111.192.152:8080的訪問被自動負載分發到了後端的兩個Pod之一10.44.0.2:8080或10.36.0.1:8080。
kubernets提供了兩種負載分發策略：RoundRobin和SessionAffinity，默認情況下采用的是RoundRobin模式進行負載。
- RoundRobin：輪詢模式
- SessionAffinity：粘性會話，將來自同一個客戶端的請求始終轉發至同一個後端的Pod對象，可以通過設置service.spec.sessionAffinity: ClientIP來啓用
5.使用配置文件方式創建svc
apiVersion: v1
kind: Service
metadata:
name: webapp
spec:
type: ClusterIP
ports:
- port: 8081
targetPort: 8080
selector:
app: webapp
ports：與後端容器端口關聯
selector：關聯到哪些pod資源上
# kubectl delete svc webapp
service "webapp" deleted
# kubectl create -f webapp-svc.yaml
service/webapp created
# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
webapp ClusterIP 10.96.231.61 <none> 8081/TCP 14s
6.多端口Service創建
apiVersion: v1
kind: Service
metadata:
name: webapp
spec:
ports:
- port: 8080
targetPort: 8080
name: web
- port: 8005
targetPort: 8005
name: management
selector:
app: webapp7.使用UDP端口模式
apiVersion: v1
kind: Service
metadata:
name: kube-dns
namespace: kube-system
labels:
k8s-app: kube-dns
kubernetes.io/cluster-service: "true"
kubernetes.io/name: "KubeDNS"
spec:
selector:
k8s-app: kube-dns
clusterIP: 169.169.0.100
ports:
- name: dns
port: 53
protocol: UDP
- name: dns-tcp
port: 53
protocol: TCP8.外部服務Service
在一些環境中，應用系統需要將一個外部數據庫作爲後端服務進行連接，這時可以通過創建一個沒有Selector的svc來實現
kind: Service
apiVersion: v1
metadata:
name: my-service
spec:
ports:
- protocol: TCP
port: 80
targetPort: 80由於這個 Service 沒有 selector，就不會創建相關的 Endpoints 對象。可以手動將 Service 映射到指定的 Endpoints：
kind: Endpoints
apiVersion: v1
metadata:
name: my-service
subsets:
- addresses:
- IP: 1.2.3.4
ports:
- port: 80三、Headless Service
有時不需要或不想要負載均衡，以及單獨的 Service IP。 遇到這種情況，可以通過指定 Cluster IP（spec.clusterIP）的值爲 "None" 來創建Headless Service，僅通過Selector將後端的Pod列表返回給調用的客戶端
創建一個Headless Service實例
apiVersion: v1
kind: Service
metadata:
labels:
app: nginx
name: nginx
spec:
ports:
- port: 80
clusterIP: None
selector:
app: nginx
# kubectl get svc
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
nginx ClusterIP None <none> 80/TCP 26s
四、從集羣外部訪問Pod或Service
1.將容器應用的端口映射到物理機
# cat pod-hostport.yaml
apiVersion: v1
kind: Pod
metadata:
name: webapp
labels:
app: webapp
spec:
containers:
- name: webapp
image: tomcat
ports:
- containerPort: 8080
hostPort: 8081此處映射的IP地址爲該Pod所在node的IP
# curl 20.0.20.103:8081
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>Apache Tomcat/8.5.42</title>
<link href="favicon.ico" rel="icon" type="image/x-icon" />
<link href="favicon.ico" rel="shortcut icon" type="image/x-icon" />
通過設置spce.hostNetwork=true，默認hostPort等於containerPort
apiVersion: v1
kind: Pod
metadata:
name: webapp
labels:
app: webapp
spec:
hostNetwork: true
containers:
- name: webapp
image: tomcat
ports:
- containerPort: 80802.將Service的端口映射到物理機
# cat webapp-rc.yaml
apiVersion: v1
kind: ReplicationController
metadata:
name: webapp
spec:
replicas: 2
template:
metadata:
name: webapp
labels:
app: webapp
spec:
containers:
- name: webapp
image: tomcat
ports:
- containerPort: 8080
# cat webapp-svcnodeport.yaml
apiVersion: v1
kind: Service
metadata:
name: webapp
spec:
type: NodePort
ports:
- port: 8080
targetPort: 8080
nodePort: 30011
selector:
app: webapp
# curl 20.0.20.101:30011
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>Apache Tomcat/8.5.42</title>
<link href="favicon.ico" rel="icon" type="image/x-icon" />
<link href="favicon.ico" rel="shortcut icon" type="image/x-icon" />