In this step, we will create a Portworx volume (PVC) for postgres.

Step: Create StorageClass and PersistentVolumeClaim

Take a look at the StorageClass definition for Portworx

cat px-repl3-sc.yaml

The parameters are declarative policies for your storage volume. Notice the "allowVolumeExpansion: true" this needs to be added for kubernetes volume expansion. See here for a full list of supported parameters.

Create the storage class using:

kubectl create -f px-repl3-sc.yaml

Take a look at the Persistent Volume Claim

cat px-postgres-pvc.yaml

This defines the maximum volume size. Portworx will thin provision the volume and let it grow to 2GB size.

Create the PersistentVolumeClaim using:

kubectl create -f px-postgres-pvc.yaml

Now that we have the volumes created, let's deploy postgres !

In this step, we will deploy the postgres application using the PersistentVolumeClaim created before.

Step: Create secret for postgres

Below we are creating a Secret to store the postgres password.

echo -n mysql123 > password.txt
kubectl create secret generic postgres-pass --from-file=password.txt

Below we will create a postgres Deployment that uses a Portworx PVC.

Take a look at the yaml: cat postgres-app.yaml

Observe the volumeMounts and volumes sections where we mount the PVC.

Now use kubectl to deploy postgres.

kubectl create -f postgres-app.yaml

Step: Verify postgres pod is ready

Below commands wait till the postgres pods are in ready state.

watch kubectl get pods -l app=postgres -o wide

When the pod is in Running state then then hit clear to ctrl-c and clear the screen.

In this step, we will use pxctl to inspect the volume

Step: Inspect the Portworx volume

Portworx ships with a pxctl command line that can be used to manage Portworx.

Below we will use pxctl to inspect the underlying volume for our PVC.

VOL=`kubectl get pvc | grep px-postgres-pvc | awk '{print $3}'`
PX_POD=$(kubectl get pods -l name=portworx -n kube-system -o jsonpath='{.items[0].metadata.name}')
kubectl exec -it $PX_POD -n kube-system -- /opt/pwx/bin/pxctl volume inspect ${VOL}

Make the following observations in the inspect output

• State indicates the volume is attached and shows the node on which it is attached. This is the node where the Kubernetes pod is running.
• HA shows the number of configured replicas for this volume
• Labels show the name of the PVC for this volume
• Replica sets on nodes shows the px nodes on which volume is replicated

Now that we have PostgreSQL up, let's proceed to creating a sample database!

In this step, we will run a bigger benchmark and run out of space to show how easy it is to add space to a volume dynamically.

Step: Open a shell inside the postgres container

Below commands exec into the postgres pod:

POD=`kubectl get pods -l app=postgres | grep Running | grep 1/1 | awk '{print $1}'`
kubectl exec -it $POD bash

Next we can launch the psql utility and create a database

psql
create database pxdemo;
\l
\q

Use pgbench to run a baseline transaction benchmark which will try to grow the volume to more than 1 Gib and fail.

pgbench -i -s 150 pxdemo

• You will see a lot of error messages, if you look at the first one it will say "No space left on device". The pod is going to fail but that's ok, we'll let STORK reschedule it. If the pod doesn't faile you will have to exit from the pod shell before proceeding.

Step: Expand the volume and run benchmark again

Since we added the allowVolumeExpansion: true attribute to our storage class you can expand the PVC by editing the px-mongo-pvc.yaml file and then re-applying this file using kubectl.

sed -i 's/1Gi/10Gi/g' px-postgres-pvc.yaml
kubectl apply -f px-postgres-pvc.yaml

Inspect the volume and verify that it now has 10Gi capacity:

kubectl get pvc px-postgres-pvc

As you can see the volume is now expanded and our MongoDB database didn't require restarting.

kubectl get pods

Now that you have expanded the volume you can go back to the step above and run the benchmark again.