Red Hat OpenShift Developer II: Building and Deploying Cloud-native Applications

Instructions

1. Log in to Red Hat OpenShift and use the deployments-stateful project.

   1. Log in to OpenShift as the developer user.

      [student@workstation ~]$ oc login -u developer -p developer \
      https://api.ocp4.example.com:6443
      Login successful.
      ...output omitted...

   2. Ensure that you use the deployments-stateful project.

      [student@workstation ~]$ oc project deployments-stateful
      Already on project "deployments-stateful" on server "https://api.ocp4.example.com:6443".

   3. Verify that the database server is running. Note that the server might take a minute to start.

      [student@workstation ~]$ oc get deploy
      NAME       READY   UP-TO-DATE   AVAILABLE   AGE
      mysql-db   1/1     1            1           1m

2. Attach a persistent volume claim (PVC) called mysql-db-pvc to the deployment, mounted to the /var/lib/mysql path within the pod.

   Important

   The configuration in this exercise demonstrates the basics of persistent storage and is not production ready.

   In a production-ready database server deployment, each replica needs to handle sharding, failover, and other high-availability tasks. Simply increasing the number of replicas with this setup will not work.

   1. Use the oc set volume command to create a PVC for the deployment.

      [student@workstation ~]$ oc set volumes deploy/mysql-db \
      --add --name nfs-volume-storage --type pvc \
      --claim-mode rwo --claim-size 1Gi --mount-path /var/lib/mysql \
      --claim-name mysql-db-pvc
      deployment.apps/mysql-db volume updated

   2. Verify that the PVC exists and has the correct attributes.

      [student@workstation ~]$ oc get pvc
      NAME           STATUS   VOLUME        CAPACITY   ACCESS MODES   STORAGECLASS   AGE
      mysql-db-pvc   Bound    pvc-f8...cc   1Gi        RWO            nfs-storage    82s

   3. Verify that the PVC is attached to the database deployment.

      [student@workstation ~]$ oc get deploy/mysql-db -o \
      jsonpath='{.spec.template.spec.containers[0].volumeMounts}' | jq
      [
        {
          "mountPath": "/var/lib/mysql",
          "name": "nfs-volume-storage"
        }
      ]

      Note

      The trailing jq tool invocation formats the JSON output of the preceding command to ease viewing.

3. Use a configuration map as an ephemeral volume to add initialization data to the database.

   1. View the contents of the init-db.sql script that initializes the database.

      [student@workstation ~]$ cd ~/DO288/labs/deployments-stateful
      [student@workstation deployments-stateful]$ cat init-db.sql
      DROP TABLE IF EXISTS `Item`;
      CREATE TABLE `Item` (`id` BIGINT not null auto_increment primary key, `description` VARCHAR(100), `done` BIT);
      INSERT INTO `Item` (`id`,`description`,`done`) VALUES (1,'Pick up newspaper', 0);
      INSERT INTO `Item` (`id`,`description`,`done`) VALUES (2,'Buy groceries', 1);

   2. Create a configuration map called init-db-cm that contains the SQL script.

      [student@workstation deployments-stateful]$ oc create cm init-db-cm \
      --from-file init-db.sql
      configmap/init-db-cm created

   3. Add the configuration map as a volume called init-db-volume to the deployment. Specify the volume type as configmap and set the /tmp/init-db directory as the mount path.

      [student@workstation deployments-stateful]$ oc set volumes deploy/mysql-db \
      --add --name init-db-volume \
      --configmap-name init-db-cm --type configmap \
      --mount-path /tmp/init-db
      deployment.apps/mysql-db volume updated

   4. Verify that the configuration map is attached to the database deployment. The list of volumes contains a new entry for the configuration map volume.

      [student@workstation deployments-stateful]$ oc get deploy/mysql-db -o \
      jsonpath='{.spec.template.spec.containers[0].volumeMounts}' | jq
      [
        {
          "mountPath": "/var/lib/mysql",
          "name": "nfs-volume-storage"
        },
        {
          "mountPath": "/tmp/init-db",
          "name": "init-db-volume"
        }
      ]

4. Run the mounted script to initialize the database and verify that the data exist.

   1. Use the mysql client to execute the database script in the /tmp/init-db volume. Ignore the warning message.

      [student@workstation deployments-stateful]$ oc rsh deploy/mysql-db mysql \
      -udbuser -pdbuser items -e "source /tmp/init-db/init-db.sql"
      ...output omitted...

   2. Verify that the table is populated.

      [student@workstation deployments-stateful]$ oc rsh deploy/mysql-db \
      mysql -udbuser -pdbuser items -e "select * from Item;"
      ...output omitted...
      +----+-------------------+------------+
      | id | description       | done       |
      +----+-------------------+------------+
      |  1 | Pick up newspaper | 0x00       |
      |  2 | Buy groceries     | 0x01       |
      +----+-------------------+------------+

5. Scale the deployment down and then back up to observe that the data persists even if the pod is destroyed.

   1. Scale down the mysql-db deployment.

      [student@workstation deployments-stateful]$ oc scale --replicas 0 deploy/mysql-db
      deployment.apps/mysql-db scaled

   2. Verify that no database server pods are running.

      [student@workstation deployments-stateful]$ oc get po
      No resources found in deployments-stateful namespace.

   3. Verify that the PVC still exists.

      [student@workstation deployments-stateful]$ oc get pvc
      NAME           STATUS   VOLUME        CAPACITY   ACCESS MODES   STORAGECLASS ...
      mysql-db-pvc   Bound    pvc-f8...cc   1Gi        RWO            nfs-storage  ...

   4. Scale up the mysql-db deployment.

      [student@workstation deployments-stateful]$ oc scale --replicas 1 deploy/mysql-db
      deployment.apps/mysql-db scaled

   5. Connect to the database pod and verify that the table data still exists.

      [student@workstation deployments-stateful]$ oc rsh deploy/mysql-db \
       mysql -udbuser -pdbuser items -e "select * from Item;"
      ...output omitted...
      +----+-------------------+------------+
      | id | description       | done       |
      +----+-------------------+------------+
      |  1 | Pick up newspaper | 0x00       |
      |  2 | Buy groceries     | 0x01       |
      +----+-------------------+------------+

6. Scale the deployment to see how all replicas use the same PVC, then delete the deployment and PVC.

   1. Scale up the mysql-db deployment.

      [student@workstation deployments-stateful]$ oc scale --replicas 3 deploy/mysql-db
      deployment.apps/mysql-db scaled

   2. Observe that still only one PVC exists.

      [student@workstation deployments-stateful oc get pvc
      NAME           STATUS   VOLUME        CAPACITY   ACCESS MODES   STORAGECLASS ...
      mysql-db-pvc   Bound    pvc-f8...cc   1Gi        RWO            nfs-storage  ...

   3. Delete the mysql-db deployment.

      [student@workstation deployments-stateful]$ oc delete deploy/mysql-db
      deployment.apps "mysql-db" deleted

   4. Delete the mysql-db-pvc PVC.

      [student@workstation deployments-stateful]$ oc delete pvc/mysql-db-pvc
      persistentvolumeclaim "mysql-db-pvc" deleted

7. Create a stateful set for the database server that mounts the configuration map and PVC.

   1. Review the mysql-stateful-set.yaml file. In particular, note the pieces that define how to create and mount the PVC and the configuration map. The stateful set is dependent on the configuration map created in a preceding step.

      [student@workstation deployments-stateful]$ cat mysql-stateful-set.yaml
      apiVersion: apps/v1
      kind: StatefulSet
      ...output omitted...
      spec:
        ...output omitted...
        template:
          ...output omitted...
          spec:
            containers:
              - image: registry.ocp4.example.com:8443/rhel8/mysql-80
                ...output omitted...
                volumeMounts:
                  - name: mysql-db-pvc
                    mountPath: /var/lib/mysql
                    subPath: mysql-db
                  - name: init-db-volume
                    mountPath: /tmp/init-db
            volumes:
              - name: init-db-volume
                configMap:
                  name: init-db-cm
        volumeClaimTemplates:
          - metadata:
              name: mysql-db-pvc
            spec:
              accessModes: [ "ReadWriteOnce" ]
              storageClassName: nfs-storage
              resources:
                requests:
                  storage: 1Gi

   2. Apply the manifest to create the stateful set. Ignore the warning.

      [student@workstation deployments-stateful]$ oc apply -f mysql-stateful-set.yaml
      ...output omitted...
      statefulset.apps/mysql-db created

   3. Observe that a database server pod is running.

      [student@workstation deployments-stateful]$ oc get po
      NAME         READY   STATUS    RESTARTS   AGE
      mysql-db-0   1/1     Running   0          42s

      Note that the pod name includes a numeric suffix. Each additional replica for the stateful set increments sequentially.

8. Initialize the database, delete the pod, and observe that the pod is recreated with the persisted data intact.

   1. Run the init-db.sql script inside the pod to initialize the database. Ignore the warning message.

      [student@workstation deployments-stateful]$ oc rsh mysql-db-0 mysql -udbuser \
      -pdbuser items -e "source /tmp/init-db/init-db.sql"
      ...output omitted...

   2. Delete the singular database server pod.

      [student@workstation deployments-stateful]$ oc delete po/mysql-db-0
      pod "mysql-db-0" deleted

   3. Observe that OpenShift recreates the pod.

      [student@workstation deployments-stateful]$ oc get po
      NAME         READY   STATUS    RESTARTS   AGE
      mysql-db-0   1/1     Running   0          22s

   4. Connect to the database pod and verify that the data still exists.

      [student@workstation deployments-stateful]$ oc rsh mysql-db-0 mysql -udbuser \
      -pdbuser items -e "select * from Item;"
      ...output omitted...
      +----+-------------------+------------+
      | id | description       | done       |
      +----+-------------------+------------+
      |  1 | Pick up newspaper | 0x00       |
      |  2 | Buy groceries     | 0x01       |
      +----+-------------------+------------+

9. Scale the stateful set to observe that each replica uses a new PVC. This is in contrast to the deployment that shared a single PVC amongst all replicas.

   1. Update the stateful set to have three replicas.

      [student@workstation deployments-stateful]$ oc scale --replicas 3 \
      statefulset/mysql-db
      statefulset.apps/mysql-db scaled

   2. Wait for the pods to start. Notice that each new pod has an incremented numeric suffix.

      [student@workstation deployments-stateful]$ oc get pod
      NAME         READY   STATUS    RESTARTS   AGE
      mysql-db-0   1/1     Running   0          3m32s
      mysql-db-1   1/1     Running   0          78s
      mysql-db-2   1/1     Running   0          74s

   3. Observe that additional PVCs exist for each new pod.

      [student@workstation deployments-stateful]$ oc get pvc
      NAME                      STATUS   VOLUME        CAPACITY   ACCESS MODES ...
      mysql-db-pvc-mysql-db-0   Bound    pvc-e9...92   1Gi        RWO          ...
      mysql-db-pvc-mysql-db-1   Bound    pvc-08...f0   1Gi        RWO          ...
      mysql-db-pvc-mysql-db-2   Bound    pvc-0e...33   1Gi        RWO          ...