> Note: This example application deployment assumes you already have an OpenShift test cluster or have followed the instructions in the Deploying OpenShift Container Storage 4 to OpenShift 4 Blog to set up an OpenShift Container Platform 4.2.14+ cluster using OpenShift Container Storage 4.

In this Blog the ocs-storagecluster-ceph-rbd storage class will be used by an OCP 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 ocs-storagecluster-cephblockpool.
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 Persistent Volume Claim (PVC) should use. Feel free to download https://raw.githubusercontent.com/red-hat-storage/ocs-training/master/ocp4ocs4/configurable-rails-app.yaml to check on the format of this template. Search for STORAGE_CLASS in the downloaded content.
oc new-project my-database-app

curl <a href="https://raw.githubusercontent.com/red-hat-storage/ocs-training/master/ocp4ocs4/configurable-rails-app.yaml">https://raw.githubusercontent.com/red-hat-storage/ocs-training/master/ocp4ocs4/configurable-rails-app.yaml</a> | oc new-app -p STORAGE_CLASS=ocs-storagecluster-ceph-rbd -p VOLUME_CAPACITY=5Gi -f -

After the deployment is started you can monitor with these commands.
oc status
oc get pvc -n my-database-app
This step could take 5 or more 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
Example output:

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. Your HOST/PORT will be different.
oc get route -n my-database-app

Example output:

rails-pgsql-persistent rails-pgsql-persistent-my-database-app.apps.cluster-a26e.sandbox449.opentlc.com rails-pgsql-persistent

Copy your rails-pgsql-persistent route (different than above) to a browser window to create articles. You will need to append /articles to the end.
Example http:///articles
Enter the username and password below to create articles and comments. 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.
username: openshift
password: secret
Lets now take another look at the Ceph ocs-storagecluster-cephblockpool created by the ocs-storagecluster-ceph-rbd Storage Class. Log into the toolbox pod again.
TOOLS_POD=$(oc get pods -n openshift-storage -l app=rook-ceph-tools -o name)
oc rsh -n openshift-storage $TOOLS_POD
Run the same Ceph commands as before the application deployment and compare to results in prior section. Notice the number of objects in ocs-storagecluster-cephblockpool has increased. The third command lists RBDs and we should now have two RBDs.

ceph df
rados df
rbd -p ocs-storagecluster-cephblockpool ls | grep vol

You can exit the toolbox by either pressing Ctrl+D or by executing exit.

Matching PVs to RBDs

A handy way to match persistent volumes to Ceph RBDs is to execute:

oc get pv -o 'custom-columns=NAME:.spec.claimRef.name,PVNAME:.metadata.name,STORAGECLASS:.spec.storageClassName,VOLUMEHANDLE:.spec.csi.volumeHandle'

Example output:

ocs-deviceset-0-0-gzxjb pvc-1cf104d2-2033-11ea-ac56-0a9ccb4b29e2 gp2
ocs-deviceset-1-0-s87xm pvc-1cf33c42-2033-11ea-ac56-0a9ccb4b29e2 gp2
ocs-deviceset-2-0-zcjk4 pvc-1cf4f825-2033-11ea-ac56-0a9ccb4b29e2 gp2
db-noobaa-core-0 pvc-3008e684-2033-11ea-a83b-065b3ec3da7c ocs-storagecluster-ceph-rbd 0001-0011-openshift-storage-0000000000000001-3c0bb177-2033-11ea-9396-0a580a800406
postgresql pvc-4ca89d3d-2060-11ea-9a42-02dfa51cba90 ocs-storagecluster-ceph-rbd 0001-0011-openshift-storage-0000000000000001-4cbba393-2060-11ea-9396-0a580a800406
rook-ceph-mon-a pvc-cac661b6-2032-11ea-ac56-0a9ccb4b29e2 gp2
rook-ceph-mon-b pvc-cde2d8b3-2032-11ea-ac56-0a9ccb4b29e2 gp2
rook-ceph-mon-c pvc-d0efbd9d-2032-11ea-ac56-0a9ccb4b29e2 gp2
lab-ossm-hub-data pvc-dc1d4bdc-2028-11ea-ad6c-0a9ccb4b29e2 gp2

The second half of the VOLUMEHANDLE column mostly matches what your RBD is named inside of Ceph. All you have to do is append csi-vol- to the front like this:
Get the full RBD name of our postgreSQL PV in one command

oc get pv pvc-4ca89d3d-2060-11ea-9a42-02dfa51cba90 -o jsonpath='{.spec.csi.volumeHandle}' | cut -d '-' -f 6- | awk '{print "csi-vol-"$1}'

> Note: You will need to adjust the above command to use your PVNAME name
Example output:
Now we can check on the details of our RBD from inside of the tools pod:

TOOLS_POD=$(oc get pods -n openshift-storage -l app=rook-ceph-tools -o name)
oc rsh -n openshift-storage $TOOLS_POD rbd -p ocs-storagecluster-cephblockpool info csi-vol-4cbba393-2060-11ea-9396-0a580a800406

Example output:

rbd image 'csi-vol-4cbba393-2060-11ea-9396-0a580a800406':
size 5 GiB in 1280 objects
order 22 (4 MiB objects)
snapshot_count: 0
id: 95e4f3973e8
block_name_prefix: rbd_data.95e4f3973e8
format: 2
features: layering
create_timestamp: Tue Dec 17 00:00:57 2019
access_timestamp: Tue Dec 17 00:00:57 2019
modify_timestamp: Tue Dec 17 00:00:57 2019

> Note: You will need to adjust the above command to use your RBD name

Resources and Feedback

To find out more about OpenShift Container Storage or to take a test drive, visit https://www.openshift.com/products/container-storage/.

If you would like to learn more about what the OpenShift Container Storage team is up to or provide feedback on any of the new 4.2 features, take this brief 3-minute survey.



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