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In Kubernetes, if you want to to provide persistence for your pods, you can use a StatefulSet. Unlike a Deployment, a StatefulSet holds on to the identity for each of its Pods which is ideal for stateful apps. A StatefulSet requires a Headless Service to be responsible for Pods' identity.


It tends to be used for single-instance apps as the underlying PersistentVolume can only be mounted to one Pod. You can use it if you don't mind data loss in environments like development, test or qa. Avoid using it in production where it makes sense. Err towards cloud based storage instead in production.


Configuration


apiVersion: v1
kind: Namespace
metadata:
name: storage

---

apiVersion: v1
kind: Service
metadata:
name: mysql
namespace: storage
labels:
app: mysql
spec:
clusterIP: None
selector:
app: mysql
ports:
- name: tcp
protocol: TCP
port: 3306

---

apiVersion: apps/v1
kind: StatefulSet
metadata:
name: mysql
namespace: storage
spec:
replicas: 1
serviceName: mysql
selector:
matchLabels:
app: mysql
template:
metadata:
labels:
app: mysql
spec:
terminationGracePeriodSeconds: 10
containers:
- name: mysql
image: mysql:5.6
ports:
- name: tpc
protocol: TCP
containerPort: 3306
env:
- name: MYSQL_ROOT_PASSWORD
value: password
volumeMounts:
- name: data
mountPath: /var/lib/mysql
volumeClaimTemplates:
- metadata:
name: data
spec:
storageClassName: standard
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi

Setup


Run $ kubectl apply -f mysql.yaml command to setup configuration above and the result should look like below.


$ kubectl -n storage get all
NAME READY STATUS RESTARTS AGE
pod/mysql-0 1/1 Running 0 11s

NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
service/mysql ClusterIP None 3306/TCP 11s

NAME READY AGE
statefulset.apps/mysql 1/1 11s

Test


Run $ kubectl -n storage port-forward service/mysql 3306:3306 command to expose MySQL service to local environment. I created a database in MySQL and added three records to it. It looks like below.


$ kubectl -n storage exec -it pod/mysql-0 -c mysql bash

root@mysql-0:/# mysql -uroot -ppassword

mysql> SHOW DATABASES;
+--------------------+
| Database |
+--------------------+
| information_schema |
| inanzzz |
| mysql |
| performance_schema |
+--------------------+
4 rows in set (0.00 sec)

mysql> USE inanzzz;
Database changed

mysql> SHOW TABLES;
+-------------------+
| Tables_in_inanzzz |
+-------------------+
| users |
+-------------------+
1 row in set (0.00 sec)

mysql> SELECT * FROM users;
+----+
| id |
+----+
| 1 |
| 2 |
| 3 |
+----+
3 rows in set (0.00 sec)

If you delete pod, service and statefulset, your data still be retained. However, if you delete namespace, it will be gone.