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/