前言
上個實驗2.3 – PV & PVC，我們將wordpress+mysql的Deployment綁定PVC，併成功將mysql的數據保存才PV存儲捲上。
但是mysql作爲數據庫應用，當水平擴展後，就是多個獨立的數據庫實例，數據彼此分離，導致應用在多個實例間的狀態不一致，那麼這個問題如何解決呢？
答案就是將mysql與wordpress進行分離，我們把wordpress看做一個支持水平擴展的無狀態應用，多個wordpress連接同一個mysql數據庫。
那麼wordpress又如何找到對應的mysql數據庫呢？答案就是通過Service
場景
將wordpress與mysql分離成兩個Deployment，併爲mysql定義Service，wordpress通過ServiceName發現mysql的實例信息，mysql的Deployment使用PVC保存數據狀態，完成後wordpress可以水平擴展爲多個實例，並且能夠保證數據一致性
本文實驗所有的源碼保存在：
https://github.com/zrbcool/blog-public/tree/master/k8s-hands-on/lab07
實戰
對Deployment進行分離
先準備好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爲mysql創建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
# 這裏可以簡單測試一下爲mysql創建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我們來測試下這個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)爲wordpress創建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連接的數據庫信息已經不再是127.0.0.1了，而是"wordpress-mysql-svc"，這樣wordpress的Pod就可以通過ServiceName連接到mysql了，我們來試試
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類型的Service暴露wordpress，我們來測試一下：
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測試OK，可以正常訪問，我們來對wordpress的Pod進行擴容，
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多次訪問網頁，發現已經狀態一致，所有請求均由一個數據庫處理，完成任務！
清除數據
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更多參考
https://kubernetes.io/docs/tasks/debug-application-cluster/debug-service/