# Guided Exercise: Manage non-Shared Storage with Stateful Sets Deploy a replicated web server by using a deployment and verify that all web server pods share a PV; and deploy a replicated MySQL database by using a stateful set and verify that each database instance gets a dedicated PV. **Outcomes** In this exercise, you deploy a web server with a shared persistent volume between the replicas, and a database server from a stateful set with dedicated persistent volumes for each instance. * Deploy a web server with persistent storage. * Add data to the persistent storage. * Scale the web server deployment and observe the data that is shared with the replicas. * Create a database server with a stateful set by using a YAML manifest file. * Verify that each instance from the stateful set has a persistent volume claim. As the `student` user on the `workstation` machine, use the `lab` command to prepare your system for this exercise. This command ensures that all resources are available for this exercise. ```plaintext [student@workstation ~]$ lab start storage-statefulsets ``` **Procedure 5.4. Instructions** 1. Create a web server deployment named `web-server`. Use the [`registry.ocp4.example.com:8443/redhattraining/hello-world-nginx:latest`](http://registry.ocp4.example.com:8443/redhattraining/hello-world-nginx:latest) container image. 1. Log in to the OpenShift cluster as the `developer` user with the `developer` password. ```plaintext [student@workstation]$ oc login -u developer -p developer \ https://api.ocp4.example.com:6443 ...output omitted... ``` 2. Change to the `storage-statefulsets` project. ```plaintext [student@workstation]$ oc project storage-statefulsets Now using project "storage-statefulsets" on server ...output omitted... ``` 3. Create the `web-server` deployment. Ignore the warning message. ```plaintext [student@workstation ~]$ oc create deployment web-server \ --image registry.ocp4.example.com:8443/redhattraining/hello-world-nginx:latest Warning: would violate PodSecurity "restricted:v1.24": ...output omitted... deployment.apps/web-server created ``` 4. Verify the deployment status. ```plaintext [student@workstation ~]$ oc get pods -l app=web-server NAME READY STATUS RESTARTS AGE web-server-7d7cb4cdc7-t7hx8 1/1 Running 0 4s ``` 2. Add the `web-pv` persistent volume to the `web-server` deployment. Use the default storage class and the following information to create the persistent volume: | Field | Value | | --- | --- | | Name | `web-pv` | | Type | `persistentVolumeClaim` | | Claim mode | `rwo` | | Claim size | `5Gi` | | Mount path | `/var/www/html` | | Claim name | `web-pv-claim` | 1. Add the `web-pv` persistent volume to the `web-server` deployment. Ignore the warning message. ```plaintext [student@workstation ~]$ oc set volumes deployment/web-server \ --add --name web-pv --type persistentVolumeClaim --claim-mode rwo \ --claim-size 5Gi --mount-path /var/www/html --claim-name web-pv-claim Warning: would violate PodSecurity "restricted:v1.24": ...output omitted... deployment.apps/web-server volume updated ``` Because a storage class was not specified with the `--claim-class` option, the command uses the default storage class to create the persistent volume. 2. Verify the deployment status. Notice that a new pod is created. ```plaintext [student@workstation ~]$ oc get pods -l app=web-server NAME READY STATUS RESTARTS AGE web-server-64689877c6-qgsvt 1/1 Running 0 5s ``` 3. Verify the persistent volume status. ```plaintext [student@workstation ~]$ oc get pvc NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE web-pv-claim Bound pvc-42...63ab 5Gi RWO nfs-storage 29s ``` The default storage class, `nfs-storage`, provisioned the persistent volume. 3. Add data to the PV by using the `exec` command. 1. List pods to retrieve the `web-server` pod name. ```plaintext [student@workstation ~]$ oc get pods NAME READY STATUS RESTARTS AGE web-server-64689877c6-mdr6f 1/1 Running 0 17m ``` The pod name might differ in your output. 2. Use the `exec` command to add the pod name that you retrieved from the previous step to the `/var/www/html/index.html` file on the pod. Then, retrieve the contents of the `/var/www/hmtl/index.html` file to confirm that the pod name is in the file. ```plaintext [student@workstation ~]$ oc exec -it pod/web-server-64689877c6-mdr6f \ -- /bin/bash -c \ 'echo "Hello, World from ${HOSTNAME}" > /var/www/html/index.html' ``` ```plaintext [student@workstation ~]$ oc exec -it pod/web-server-64689877c6-mdr6f \ -- cat /var/www/html/index.html Hello, World from web-server-64689877c6-mdr6f ``` 4. Scale the `web-server` deployment to two replicas and confirm that an additional pod is created. 1. Scale the `web-server` deployment to two replicas. ```plaintext [student@workstation ~]$ oc scale deployment web-server --replicas 2 deployment.apps/web-server scaled ``` 2. Verify the replica status and retrieve the pod names. ```plaintext [student@workstation ~]$ oc get pods NAME READY STATUS RESTARTS AGE web-server-64689877c6-mbj6g 1/1 Running 0 2s web-server-64689877c6-mdr6f 1/1 Running 0 17m ``` The pod names might differ from your output. 5. Retrieve the content of the `/var/www/html/index.html` file on the `web-server` pods by using the `oc exec` command to verify that the file is the same in both pods. 1. Verify that the `/var/www/html/index.html` file is the same in both pods. ```plaintext [student@workstation ~]$ oc exec -it pod/web-server-64689877c6-mbj6g \ -- cat /var/www/html/index.html Hello, World from web-server-64689877c6-mdr6f ``` ```plaintext [student@workstation ~]$ oc exec -it pod/web-server-64689877c6-mdr6f \ -- cat /var/www/html/index.html Hello, World from web-server-64689877c6-mdr6f ``` Notice that both files show the name of the first instance, because they share the persistent volume. 6. Create a database server with a stateful set by using the `statefulset-db.yml` file in the `/home/student/DO180/labs/storage-statefulsets` directory. Update the file with the following information: | Field | Value | | --- | --- | | [`metadata.name`](http://metadata.name) | `dbserver` | | [`spec.selector.matchLabels.app`](http://spec.selector.matchLabels.app) | `database` | | [`spec.template.metadata.labels.app`](http://spec.template.metadata.labels.app) | `database` | | [`spec.template.spec.containers.name`](http://spec.template.spec.containers.name) | `dbserver` | | [`spec.template.spec.containers.volumeMounts.name`](http://spec.template.spec.containers.volumeMounts.name) | `data` | | `spec.template.spec.containers.volumeMounts.mountPath` | `/var/lib/mysql` | | [`spec.volumeClaimTemplates.metadata.name`](http://spec.volumeClaimTemplates.metadata.name) | `data` | | `spec.volumeClaimTemplates.spec.storageClassName` | `lvms-vg1` | 1. Open the `/home/student/DO180/labs/storage-statefulsets/statefulset-db.yml` file in an editor. Replace the `` objects with values from the previous table: ```plaintext apiVersion: apps/v1 kind: StatefulSet metadata: name: dbserver spec: selector: matchLabels: app: database replicas: 2 template: metadata: labels: app: database spec: terminationGracePeriodSeconds: 10 containers: - name: dbserver image: registry.ocp4.example.com:8443/redhattraining/mysql-app:v1 ports: - name: database containerPort: 3306 env: - name: MYSQL_USER value: "redhat" - name: MYSQL_PASSWORD value: "redhat123" - name: MYSQL_DATABASE value: "sakila" volumeMounts: - name: data mountPath: /var/lib/mysql volumeClaimTemplates: - metadata: name: data spec: accessModes: [ "ReadWriteOnce" ] storageClassName: "lvms-vg1" resources: requests: storage: 1Gi ``` 2. Create the database server by using the `oc create -f /home/student/DO180/labs/storage-statefulsets/statefulset-db.yml` command. Ignore the warning message. ```plaintext [student@workstation ~]$ oc create -f \ /home/student/DO180/labs/storage-statefulsets/statefulset-db.yml Warning: would violate PodSecurity "restricted:v1.24": ...output omitted... statefulset.apps/bdserver created ``` 3. Wait a few moments and then verify the status of the stateful set and its instances. ```plaintext [student@workstation ~]$ oc get statefulset NAME READY AGE dbserver 2/2 10s ``` ```plaintext [student@workstation ~]$ oc get pods -l app=database NAME READY STATUS ... dbserver-0 1/1 Running ... dbserver-1 1/1 Running ... ``` 4. Use the `exec` command to add data to each of the stateful set pods. ```plaintext [student@workstation ~]$ oc exec -it pod/dbserver-0 -- /bin/bash -c \ "mysql -uredhat -predhat123 sakila -e 'create table items (count INT);'" mysql: [Warning] Using a password on the command line interface can be insecure. ``` ```plaintext [student@workstation ~]$ oc exec -it pod/dbserver-1 -- /bin/bash -c \ "mysql -uredhat -predhat123 sakila -e 'create table inventory (count INT);'" mysql: [Warning] Using a password on the command line interface can be insecure. ``` 7. Confirm that each instance from the `dbserver` stateful set has a persistent volume claim. Then, verify that each persistent volume claim contains unique data. 1. Confirm that the persistent volume claims have a `Bound` status. ```plaintext [student@workstation ~]$ oc get pvc -l app=database NAME STATUS ... CAPACITY ACCESS MODE ... data-dbserver-0 Bound ... 1Gi RWO ... data-dbserver-1 Bound ... 1Gi RWO ... ``` 2. Verify that each instance from the `dbserver` stateful set has its own persistent volume claim by using the `oc get pod pod-name -o json | jq .spec.volumes[0].persistentVolumeClaim.claimName` command. ```plaintext [student@workstation ~]$ oc get pod dbserver-0 -o json | \ jq .spec.volumes[0].persistentVolumeClaim.claimName "data-dbserver-0" ``` ```plaintext [student@workstation ~]$ oc get pod dbserver-1 -o json | \ jq .spec.volumes[0].persistentVolumeClaim.claimName "data-dbserver-1" ``` 3. Application-level clustering is not enabled for the `dbserver` stateful set. Verify that each instance of the `dbserver` stateful set has unique data. ```plaintext [student@workstation ~]$ oc exec -it pod/dbserver-0 -- /bin/bash -c \ "mysql -uredhat -predhat123 sakila -e 'show tables;'" mysql: [Warning] Using a password on the command line interface can be insecure. ------------------ | Tables_in_sakila | ------------------ | items | ------------------ ``` ```plaintext [student@workstation ~]$ oc exec -it pod/dbserver-1 -- /bin/bash -c \ "mysql -uredhat -predhat123 sakila -e 'show tables;'" mysql: [Warning] Using a password on the command line interface can be insecure. ------------------ | Tables_in_sakila | ------------------ | inventory | ------------------ ``` 8. Delete a pod in the `dbserver` stateful set. Confirm that a new pod is created and that the pod uses the PVC from the previous pod. Verify that the previously added table exists in the `sakila` database. 1. Delete the `dbserver-0` pod in the `dbserver` stateful set. Confirm that a new pod is generated for the stateful set. Then, confirm that the `data-dbserver-0` PVC still exists. ```plaintext [student@workstation ~]$ oc delete pod dbserver-0 pod "dbserver-0" deleted ``` ```plaintext [student@workstation ~]$ oc get pods -l app=database NAME READY STATUS RESTARTS AGE dbserver-0 1/1 Running 0 4s dbserver-1 1/1 Running 0 5m ``` ```plaintext [student@workstation ~]$ oc get pvc -l app=database NAME STATUS ... CAPACITY ACCESS MODE ... data-dbserver-0 Bound ... 1Gi RWO ... data-dbserver-1 Bound ... 1Gi RWO ... ``` 2. Use the `exec` command to verify that the new `dbserver-0` pod has the `items` table in the `sakila` database. ```plaintext [student@workstation ~]$ oc exec -it pod/dbserver-0 -- /bin/bash -c \ "mysql -uredhat -predhat123 sakila -e 'show tables;'" mysql: [Warning] Using a password on the command line interface can be insecure. ------------------ | Tables_in_sakila | ------------------ | items | ------------------ ``` **Finish** On the `workstation` machine, use the `lab` command to complete this exercise. This step is important to ensure that resources from previous exercises do not impact upcoming exercises. ```plaintext [student@workstation ~]$ lab finish storage-statefulsets ```