elmiko's notes

In my last article I talked about how to setup an okd 3.11 all-in-one installation. The install that results from those instructions is quite bare. Something that I’ve had to do for various applications I want to run, is to create peristent storage.

In Kubernetes, the main way to interact with persisten storage is through the PersistentVolume and PersistentVolumeClaim objects.

In a full cloud-based deployment storage can be a very nebulous thing from a user perspective. It’s there, and it’s backed by some drives somewhere. This isn’t quite good enough for my local development machine, I need to be able to debug applications that use persistent storage. To that end, there is a great backend called hostVolume which allows mapping a local volume on the host to a PersistentVolume in Kubernetes. This is perfect for my single machine deploy.

Adding a local hostVolume

To begin, i need to create the directories that will be the individual volumes.

sudo mkdir -p /mnt/openshift-pv/pv1 /mnt/openshift-pv/pv2 \
              /mnt/openshift-pv/pv3 /mnt/openshift-pv/pv4 \
              /mnt/openshift-pv/pv5

Next I allow group write into these folders to ensure that my workloads will be able to actually write stuff.

sudo chmod g+w -R /mnt/openshift-pv

And lastly I need to adjust the SELinux security context so that the kernel will allow containers to use these directories.

sudo chcon -R unconfined_u:object_r:svirt_sandbox_file_t:s0 /mnt/openshift-pv

With these commands the host is now ready to accept the linkage to Kubernetes for the PersistentVolumes. To enable this on Kubernetes I need to apply the appropriate object definitions to the API server.

shift.opb.studios-pv.yaml

kind: List
apiVersion: v1
metadata: {}

items:
  - apiVersion: v1
    kind: PersistentVolume
    metadata:
      name: pv1
    spec:
      capacity:
        storage: 10Gi
      accessModes:
        - ReadWriteOnce
      persistentVolumeClaim: Retain
      hostPath:
        path: /mnt/openshift-pv/pv1
  - apiVersion: v1
    kind: PersistentVolume
    metadata:
      name: pv2
    spec:
      capacity:
        storage: 10Gi
      accessModes:
        - ReadWriteOnce
      persistentVolumeClaim: Retain
      hostPath:
        path: /mnt/openshift-pv/pv2
  - apiVersion: v1
    kind: PersistentVolume
    metadata:
      name: pv3
    spec:
      capacity:
        storage: 10Gi
      accessModes:
        - ReadWriteOnce
      persistentVolumeClaim: Retain
      hostPath:
        path: /mnt/openshift-pv/pv3
  - apiVersion: v1
    kind: PersistentVolume
    metadata:
      name: pv4
    spec:
      capacity:
        storage: 10Gi
      accessModes:
        - ReadWriteOnce
      persistentVolumeClaim: Retain
      hostPath:
        path: /mnt/openshift-pv/pv4
  - apiVersion: v1
    kind: PersistentVolume
    metadata:
      name: pv5
    spec:
      capacity:
        storage: 10Gi
      accessModes:
        - ReadWriteOnce
      persistentVolumeClaim: Retain
      hostPath:
        path: /mnt/openshift-pv/pv5

I apply this manifest

oc apply -f shift.opb.studios-pv.yaml

and then verify that the PersistentVolumes have been created

$ oc get pv
NAME   CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM   STORAGECLASS   REASON   AGE
pv1    10Gi       RWO            Retain           Available                                   1m
pv2    10Gi       RWO            Retain           Available                                   1m
pv3    10Gi       RWO            Retain           Available                                   1m
pv4    10Gi       RWO            Retain           Available                                   1m
pv5    10Gi       RWO            Retain           Available                                   1m

Excellent! I can know create objects that require PersistentVolumeClaims.

update Something to keep in mind about these insttructions is that the reclaim policy of Retain will prevent these volume claims from being released when they are not being used. If this behavior is causing you problems, try using the Recycle policy instead.

I hope these instructions are helpful, and as always happy hacking =)

Adding hostVolume persistent volumes to my okd 3.11 install

Adding a local hostVolume