Persistent Volumes
A PersistentVolume (PV) is a piece of storage in the cluster that has been manually provisioned by an administrator, or dynamically provisioned by Kubernetes using a StorageClass.
A PersistentVolumeClaim (PVC) is a request for storage by a user that can be fulfilled by a PV.
PersistentVolumes and PersistentVolumeClaims are independent from Pod lifecycles and preserve data through restarting, rescheduling, and even deleting Pods.
Using Persistent Disks with WordPress and MySQL
Create your PersistentVolumes and PersistentVolumeClaims
cat << EOF > mysql-volumeclaim.yaml
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
name: mysql-volumeclaim
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 200Gi
EOF
cat << EOF > wordpress-volumeclaim.yaml
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
name: wordpress-volumeclaim
spec:
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 200Gi
EOF
{
kubectl apply -f mysql-volumeclaim.yaml
kubectl apply -f wordpress-volumeclaim.yaml
}
persistentvolumeclaim/mysql-volumeclaim created
persistentvolumeclaim/wordpress-volumeclaim created
kubectl get pvc
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
mysql-volumeclaim Bound pvc-4323fc71-dad4-11e9-9b6e-42010a800fef 200Gi RWO standard 26s
wordpress-volumeclaim Bound pvc-434ee838-dad4-11e9-9b6e-42010a800fef 200Gi RWO standard 26s
Set up MySQL
Deploy MySQL
kubectl create secret generic mysql --from-literal=password=YOUR_PASSWORD
secret/mysql created
cat << EOF > mysql.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: mysql
labels:
app: mysql
spec:
replicas: 1
selector:
matchLabels:
app: mysql
template:
metadata:
labels:
app: mysql
spec:
containers:
- image: mysql:5.6
name: mysql
env:
- name: MYSQL_ROOT_PASSWORD
valueFrom:
secretKeyRef:
name: mysql
key: password
ports:
- containerPort: 3306
name: mysql
volumeMounts:
- name: mysql-persistent-storage
mountPath: /var/lib/mysql
volumes:
- name: mysql-persistent-storage
persistentVolumeClaim:
claimName: mysql-volumeclaim
EOF
kubectl create -f mysql.yaml
deployment.apps/mysql created
kubectl get pod -l app=mysql -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
mysql-674dcfbd85-9k4k9 1/1 Running 0 41s 10.24.0.3 gke-admatic-cluster-1-default-pool-902caf66-2j0p <none> <none>
Create MySQL service
cat << EOF > mysql-service.yaml
apiVersion: v1
kind: Service
metadata:
name: mysql
labels:
app: mysql
spec:
type: ClusterIP
ports:
- port: 3306
selector:
app: mysql
EOF
{
kubectl create -f mysql-service.yaml
kubectl get service mysql
}
service/mysql created
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
mysql ClusterIP 10.28.4.219 <none> 3306/TCP 0s
Set up WordPress
Deploy WordPress
cat << EOF > wordpress.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: wordpress
labels:
app: wordpress
spec:
replicas: 1
selector:
matchLabels:
app: wordpress
template:
metadata:
labels:
app: wordpress
spec:
containers:
- image: wordpress
name: wordpress
env:
- name: WORDPRESS_DB_HOST
value: mysql:3306
- name: WORDPRESS_DB_PASSWORD
valueFrom:
secretKeyRef:
name: mysql
key: password
ports:
- containerPort: 80
name: wordpress
volumeMounts:
- name: wordpress-persistent-storage
mountPath: /var/www/html
volumes:
- name: wordpress-persistent-storage
persistentVolumeClaim:
claimName: wordpress-volumeclaim
EOF
kubectl create -f wordpress.yaml
deployment.apps/wordpress created
kubectl get pod -l app=wordpress -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
wordpress-77bc8b5f57-khbbv 1/1 Running 0 52s 10.24.0.4 gke-admatic-cluster-1-default-pool-902caf66-2j0p <none> <none>
Expose WordPress Service
cat << EOF > wordpress-service.yaml
apiVersion: v1
kind: Service
metadata:
labels:
app: wordpress
name: wordpress
spec:
type: LoadBalancer
ports:
- port: 80
targetPort: 80
protocol: TCP
selector:
app: wordpress
EOF
kubectl create -f wordpress-service.yaml
service "wordpress" created
kubectl get svc -l app=wordpress
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
wordpress LoadBalancer 10.28.4.221 35.208.130.178 80:30864/TCP 87s
Visit your new WordPress blog
After finding out the IP address of your blog, point your browser to this IP address and you will see the WordPress installation screen
Once you complete the WordPress setup, point your browser to the IP address of the WordPress app again to visit your blog.
Test data persistence on failure
With PersistentVolumes, your data lives outside the application container. When your container becomes unavailable and gets rescheduled onto another compute instance by Kubernetes, Kubernetes Engine will make the PersistentVolume available on the instance that started running the Pod.
kubectl get pods -o=wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
mysql-674dcfbd85-9k4k9 1/1 Running 0 9m19s 10.24.0.3 gke-admatic-cluster-1-default-pool-902caf66-2j0p <none> <none>
wordpress-77bc8b5f57-khbbv 1/1 Running 0 7m9s 10.24.0.4 gke-admatic-cluster-1-default-pool-902caf66-2j0p <none> <none>
kubectl delete pod -l app=mysql
pod "mysql-674dcfbd85-9k4k9" deleted
kubectl get pods -o=wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
mysql-674dcfbd85-t6qp8 1/1 Running 0 5s 10.24.0.5 gke-admatic-cluster-1-default-pool-902caf66-2j0p <none> <none>
wordpress-77bc8b5f57-khbbv 1/1 Running 0 11m 10.24.0.4 gke-admatic-cluster-1-default-pool-902caf66-2j0p <none> <none>
Visit your blog again to see that the website is functioning properly and the data is persisted even though you deleted your Pod and the Pod is scheduled to another instance in your cluster.
kubectl exec mysql-674dcfbd85-t6qp8 -it -- bash
root@mysql-674dcfbd85-t6qp8:/#
mysql -u root -p
Enter password: YOUR_PASSWORD
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.6.45 MySQL Community Server (GPL)
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
SHOW DATABASES;
+---------------------+
| Database |
+---------------------+
| information_schema |
| #mysql50#lost+found |
| mysql |
| performance_schema |
| wordpress |
+---------------------+
5 rows in set (0.00 sec)
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
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)
SELECT ID,post_author,post_date,post_name from wp_posts;
+----+-------------+---------------------+----------------+
| ID | post_author | post_date | post_name |
+----+-------------+---------------------+----------------+
| 1 | 1 | 2019-09-19 12:01:22 | hello-world |
| 2 | 1 | 2019-09-19 12:01:22 | sample-page |
| 3 | 1 | 2019-09-19 12:01:22 | privacy-policy |
+----+-------------+---------------------+----------------+
3 rows in set (0.00 sec)