K8S自己动手系列 - 2.4 - Service

前言

上个实验2.3 – PV & PVC，我们将wordpress+mysql的Deployment绑定PVC，并成功将mysql的数据保存才PV存储卷上。
但是mysql作为数据库应用，当水平扩展后，就是多个独立的数据库实例，数据彼此分离，导致应用在多个实例间的状态不一致，那么这个问题如何解决呢？

答案就是将mysql与wordpress进行分离，我们把wordpress看做一个支持水平扩展的无状态应用，多个wordpress连接同一个mysql数据库。

那么wordpress又如何找到对应的mysql数据库呢？答案就是通过Service

场景

将wordpress与mysql分离成两个Deployment，并为mysql定义Service，wordpress通过ServiceName发现mysql的实例信息，mysql的Deployment使用PVC保存数据状态，完成后wordpress可以水平扩展为多个实例，并且能够保证数据一致性

本文实验所有的源码保存在：
https://github.com/zrbcool/blog-public/tree/master/k8s-hands-on/lab07

实战

对Deployment进行分离

先准备好PVC及PV

 lab07 git:(master) kubectl apply -f 01-1-mysql-pvc.yaml persistentvolumeclaim/wordpress-mysql-pv-claim created lab07 git:(master) kubectl apply -f 01-2-mysql-pv.yaml persistentvolume/wordpress-mysql-pv-volume created lab07 git:(master) kubectl get pvc NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE wordpress-mysql-pv-claim Bound wordpress-mysql-pv-volume 2Gi RWO 15s

为mysql创建Deployment

 lab07 git:(master) cat 01-3-mysql-deployment.yaml apiVersion: extensions/v1beta1 kind: Deployment metadata: labels: app: wordpress type: mysql name: wordpress-mysql spec: replicas: 1 selector: matchLabels: app: wordpress type: mysql template: metadata: labels: app: wordpress type: mysql spec: containers: - image: mysql:5.7.26 imagePullPolicy: IfNotPresent name: mysql env: - name: MYSQL_ROOT_PASSWORD value: "passw0rd" - name: MYSQL_DATABASE value: "wordpress" volumeMounts: - name: mysql-persistent-storage mountPath: /var/lib/mysql volumes: - name: mysql-persistent-storage persistentVolumeClaim: claimName: wordpress-mysql-pv-claim lab07 git:(master) kubectl apply -f 01-3-mysql-deployment.yaml deployment.extensions/wordpress-mysql created # 这里可以简单测试一下

为mysql创建Service

 lab07 git:(master) cat 01-4-mysql-svc.yaml apiVersion: v1 kind: Service metadata: name: wordpress-mysql-svc labels: app: wordpress type: mysql spec: ports: - port: 3306 protocol: TCP targetPort: 3306 selector: app: wordpress type: mysql lab07 git:(master) kubectl apply -f 01-4-mysql-svc.yaml service/wordpress-mysql-svc created lab07 git:(master) kubectl get svc -o wide NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE SELECTOR wordpress-mysql-svc ClusterIP 10.98.45.79 <none> 3306/TCP 9s app=wordpress,type=mysql

我们来测试下这个Service是否work，

 lab07 git:(master) kubectl run -it --rm --image=mysql:5.7.26 --restart=Never mysql-client -- mysql -h wordpress-mysql-svc -ppassw0rd If you don't see a command prompt, try pressing enter. mysql> use wordpress Reading table information for completion of table and column names You can turn off this feature to get a quicker startup with -A Database changed mysql> show tables; +-----------------------+ | Tables_in_wordpress | +-----------------------+ | wp_commentmeta | | wp_comments | | wp_links | | wp_options | | wp_postmeta | | wp_posts | | wp_term_relationships | | wp_term_taxonomy | | wp_termmeta | | wp_terms | | wp_usermeta | | wp_users | +-----------------------+ 12 rows in set (0.00 sec)

为wordpress创建Deployment

 lab07 git:(master) cat 02-1-wordpress-deployment.yaml apiVersion: extensions/v1beta1 kind: Deployment metadata: labels: app: wordpress type: wordpress name: wordpress-wp spec: replicas: 1 selector: matchLabels: app: wordpress type: wordpress template: metadata: labels: app: wordpress type: wordpress spec: containers: - image: wordpress:latest imagePullPolicy: IfNotPresent name: wordpress env: - name: WORDPRESS_DB_HOST value: "wordpress-mysql-svc" - name: WORDPRESS_DB_USER value: "root" - name: WORDPRESS_DB_PASSWORD value: "passw0rd"

需要注意到wordpress连接的数据库信息已经不再是127.0.0.1了，而是"wordpress-mysql-svc"，这样wordpress的Pod就可以通过ServiceName连接到mysql了，我们来试试

 lab07 git:(master) kubectl apply -f 02-1-wordpress-deployment.yaml deployment.extensions/wordpress-wp created ne> lab07 git:(master) kubectl get pods NAME READY STATUS RESTARTS AGE wordpress-mysql-66df4d4dd6-gwjsx 1/1 Running 0 19m wordpress-wp-66ffcc84c5-tgbsc 1/1 Running 0 55s

使用NodePort类型的Service暴露wordpress，我们来测试一下：

 lab07 git:(master) cat 02-2-wordpress-svc.yaml apiVersion: v1 kind: Service metadata: name: wordpress-svc labels: app: wordpress spec: ports: - port: 80 protocol: TCP targetPort: 80 nodePort: 30611 selector: app: wordpress type: NodePort lab07 git:(master) kubectl apply -f 02-2-wordpress-svc.yaml service/wordpress-svc created

测试OK，可以正常访问，我们来对wordpress的Pod进行扩容，

 lab07 git:(master) kubectl scale --replicas=5 deploy/wordpress-wp deployment.extensions/wordpress-wp scaled lab07 git:(master) kubectl get pods NAME READY STATUS RESTARTS AGE wordpress-mysql-66df4d4dd6-gwjsx 1/1 Running 0 23m wordpress-wp-66ffcc84c5-76tsh 1/1 Running 0 41s wordpress-wp-66ffcc84c5-c4r4q 1/1 Running 0 41s wordpress-wp-66ffcc84c5-qrv2r 1/1 Running 0 41s wordpress-wp-66ffcc84c5-tgbsc 1/1 Running 0 5m24s wordpress-wp-66ffcc84c5-w24sv 1/1 Running 0 41s

多次访问网页，发现已经状态一致，所有请求均由一个数据库处理，完成任务！

清除数据

 lab07 git:(master) kubectl delete -f . persistentvolumeclaim "wordpress-mysql-pv-claim" deleted persistentvolume "wordpress-mysql-pv-volume" deleted deployment.extensions "wordpress-mysql" deleted service "wordpress-mysql-svc" deleted deployment.extensions "wordpress-wp" deleted service "wordpress-svc" deleted

更多参考

https://kubernetes.io/docs/tasks/debug-application-cluster/debug-service/