Make your first steps with the three persistent storage options in Openshift.
In this scenario, we will discover three different persistent storage options:
- RWO storage - suited for low-latency, high-performance applications like databases
- RWX storage - suited for distributed applications that need a common place to store data
- OBC storage - used to get application specific access credentials for object storage buckets
Making Persistent Storage Calls in Your Application
Using RWO storage
RWO storage is the most basic type of storage that is supported by most dynamic storage provisioners in the Kuberneted eco system.
With Openshift Container Storage (OCS), each RWO storage device is backed by its own block device, which means that it is well suited for high-IOPs and low-latency operations that are common for database workloads.
In this section the
ocs-storagecluster-ceph-rbd storage class will be used by an Openshift application + database deployment to create RWO (ReadWriteOnce) persistent storage. The persistent storage will be a Ceph RBD (RADOS Block Device) volume (object) in the Ceph pool
To do so we have created a template file, based on the OpenShift rails-pgsql-persistent template, that includes an extra parameter STORAGE_CLASS that enables the end user to specify the storage class the PVC (Persistent Volume Claim) should use.
oc new-project my-database-app oc new-app rwo_rails_app.yaml -p STORAGE_CLASS=ocs-storagecluster-ceph-rbd -p VOLUME_CAPACITY=5Gi
After the deployment is started you can monitor with these commands.
Check the PVC that were created.
oc get pvc -n my-database-app
This step could take a few minutes. Wait until there are 2 Pods in
Running STATUS and 4 Pods in
Completed STATUS as shown below.
watch oc get pods -n my-database-app
NAME READY STATUS RESTARTS AGE postgresql-1-deploy 0/1 Completed 0 5m48s postgresql-1-lf7qt 1/1 Running 0 5m40s rails-pgsql-persistent-1-build 0/1 Completed 0 5m49s rails-pgsql-persistent-1-deploy 0/1 Completed 0 3m36s rails-pgsql-persistent-1-hook-pre 0/1 Completed 0 3m28s rails-pgsql-persistent-1-pjh6q 1/1 Running 0 3m14s
You can exit by pressing Ctrl+C
Once the deployment is complete you can now test the application and the persistent storage on Ceph:
The articles and comments are saved in a PostgreSQL database which stores its table spaces on the Ceph RBD volume provisioned using the
ocs-storagecluster-ceph-rbd storageclass during the application deployment.
To log in, use the following credentials:
username: openshift password: secret
If you want to clean your screen before continuing, just execute: