Last updated on August 3rd, 2022 at 08:24 am
In this tutorial we are going to deep dive in to deploying MySQL database using persistent volumes. Simple approach without much complexity.
Let us break this in to multiple steps for easier understanding
- What are PODS?
- Create StatefulSet with Persistent Volume
- Create MySQL service
- Test MySQL connectivity
- Test MySQL data persistence
What are PODS?
POD represent single instance of a running process in your K8 cluster. PODs are ephemeral, If a POD running on a node fails it will get delete and all resources associated with the POD such as storage(volume) also get destroyed. In other words volume associated with a POD exist as long as the POD is up and running.
When the POD get destroyed even if an identical replacement is created, the related volume is also destroyed. This means that you will get a brand new POD with a new volume. Read more about pod lifecycle here.
Persistent volume(PV) is a storage concept within cluster provisioned using Storage Classes. PV’s are plugins that has a lifecycle independent of the POD. PersistentVolumeClaim (PVC) is a request for storage by a user. More details about PVC and PV
In this example we are using DigitalOcean managed Kubernetes service to deploy MySQL.
StatefulSet with Persistent Volume
For storage volumes to provide persistence StatefulSets can be used. Although individual Pods are still prone to failure, StatefulSet make it easier to match existing volumes to the new Pods when they get replaced.
Save the below YAML file as mysql_digital_ocean.yml . Update the MySQL password under env section according to your choice.
apiVersion: apps/v1 kind: StatefulSet metadata: name: new-mysql-statefulset spec: replicas: 1 serviceName: mysql selector: matchLabels: app: new-mysql template: metadata: labels: app: new-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: new-mysql-data-claim mountPath: /var/lib/mysql volumeClaimTemplates: - metadata: name: new-mysql-data-claim spec: accessModes: - ReadWriteOnce resources: requests: storage: 1Gi
Next step is to use kubectl to read the file and create StatefulSet, Read more on VolumeClaimTemplates
$ kubectl apply -f mysql_digital_ocean.yml statefulset.apps/new-mysql-statefulset created $
Once you get the above message after applying the YAML file, run the kubectl get command to see the status of Statefulset, Pods and PVC
$ kubectl get statefulset NAME READY AGE new-mysql-statefulset 1/1 33s $ kubectl get pods NAME READY STATUS RESTARTS AGE new-mysql-statefulset-0 1/1 Running 0 36s $ kubectl get pvc NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE new-mysql-data-claim-new-mysql-statefulset-0 Bound pvc-7730911c-c30e-40a9-b3d7-4935cabd8865 1Gi RWO do-block-storage 50m $
From the output we can see that it created a
StatefulSet named new-mysql-statefulset
Pod was created with name new-mysql-statefulset-0
PVC name new-mysql-data-claim-new-mysql-statefulset-0
Create MySQL Service
Now that we have the MySQL container in place let us create a service for MySQL so that external applications can connect to the container. Name the file as mysql_service.yml
apiVersion: v1 kind: Service metadata: name: new-mysql-service labels: app: new-mysql-statefulset spec: selector: app: new-mysql ports: - name: tcp protocol: TCP port: 3306 targetPort: 3306
Once the file is created run this command
$ kubectl apply -f mysql_service.yml service/new-mysql-service created $
Run the describe pod command to see the details of the service we just created.
$ kubectl describe service/new-mysql-service Name: new-mysql-service Namespace: default Labels: app=new-mysql-statefulset Annotations: <none> Selector: app=new-mysql Type: ClusterIP IP Family Policy: SingleStack IP Families: IPv4 IP: 10.245.252.95 IPs: 10.245.252.95 Port: tcp 3306/TCP TargetPort: 3306/TCP Endpoints: 10.244.0.22:3306 Session Affinity: None Events: <none> [email protected] Good_Working
Keep an eye of the attribute name Endpoints, it says
Endpoints: 10.244.0.22:3306 .
Run the get pod command with -o wide option to see our mysql pod ip address and make sure that the Endpoint above matches.
$ kubectl get pods -o wide NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES new-mysql-statefulset-0 1/1 Running 0 10m 10.244.0.22
Let us check the MySQL service details
$ kubectl get services NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE new-mysql-service ClusterIP 10.245.252.95 <none> 3306/TCP 3d18h $
Cluster IP is 10.245.252.95, you can connect to the MySQL database using this IP and port number is 3306. Database connection details configured within your application has to be updated using the above details.
Using a service for your MySQL database ensures that your application is not dependent on the POD lifecycle and associated IP addresses. All you have to worry about is the MySQL ClusterIP service IP address as shown above.
Test MySQL connectivity
Now that you have your MySQL service up and running let us connect to MySQL running on Kubernetes by
1] Creating a database and table
2] Insert data to the table
Before we create a database we need to connect to the pod.
$ kubectl get pods
Using the get pods command we will get the name of the pod. In this case it will be new-mysql-statefulset-0
Now use kubectl exec command to connect to and then issue the mysql command to connect to the MySQL server inside the pod as shown. Password will be “password” (From mysql_digital_ocean.yml )
$ kubectl -it exec new-mysql-statefulset-0 -- /bin/bash [email protected]:/# mysql -u root -p
Once inside the mysql prompt, run these
mysql> create database test_mistonline; Query OK, 1 row affected (0.01 sec) mysql> use test_mistonline; Database changed mysql> CREATE TABLE kube_first (ID int,Name varchar(255) ,Address varchar(255),City varchar(255)); Query OK, 0 rows affected (0.13 sec) mysql> INSERT INTO kube_first (ID,Name,Address,City) VALUES ('1','Steve','1st Street', 'Seattle'); Query OK, 1 row affected (0.01 sec) mysql> select * from kube_first; +------+-------+------------+---------+ | ID | Name | Address | City | +------+-------+------------+---------+ | 1 | Steve | 1st Street | Seattle | +------+-------+------------+---------+ 1 row in set (0.00 sec) mysql>
As you can see above we created a database and a table, then inserted some data in to the table inside the POD.
Test MySQL Data Persistence
This is the final step in our deployment to test whether the data we created above persist if the POD is destroyed. Let’s do that now. We are deleting the pod using the kubectl delete command.
$ kubectl get pods NAME READY STATUS RESTARTS AGE new-mysql-statefulset-0 1/1 Running 0 3d18h $ kubectl delete pod/new-mysql-statefulset-0 pod "new-mysql-statefulset-0" deleted $ kubectl get pods NAME READY STATUS RESTARTS AGE new-mysql-statefulset-0 0/1 ContainerCreating 0 3s $ kubectl get pods NAME READY STATUS RESTARTS AGE new-mysql-statefulset-0 1/1 Running 0 39s
As you can see the pod got deleted and then recreated automatically. Next step is to check whether the database and table we created before the POD got destroyed are still available.
$ kubectl -it exec new-mysql-statefulset-0 -- /bin/bash [email protected]:/# mysql -u root -p Enter password: Welcome to the MySQL monitor. Commands end with ; or \g. Your MySQL connection id is 2 Server version: 5.6.51 MySQL Community Server (GPL) Copyright (c) 2000, 2021, 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 | | test_mistonline | +---------------------+ 5 rows in set (0.00 sec) mysql> select * from test_mistonline.kube_first; +------+-------+------------+---------+ | ID | Name | Address | City | +------+-------+------------+---------+ | 1 | Steve | 1st Street | Seattle | +------+-------+------------+---------+ 1 row in set (0.00 sec) mysql>
I logged in to the newly created pod and boom I do have the data inside my MySQL table intact. Awesome!!
Hope this tutorial gave you insight on how data persistence works in Kubernetes when you have a database pod running.