Updating the objects

Warning

Unfortunately, Minikube cannot handle the PVC/PV resizing, as it uses the HostPath provider internally. You can either skip this step of the tutorial, or you can use an external Kubernetes cluster with real dynamically sized volumes.

Previously (Creating the objects), we have implemented a handler for the creation of an EphemeralVolumeClaim (EVC), and created the corresponding PersistantVolumeClaim (PVC).

What will happen if we change the size of the EVC when it already exists? The PVC must be updated accordingly to match its parent EVC.

First, we have to remember the name of the created PVC: Let’s extend the creation handler we already have from the previous step with one additional line:

ephemeral.py

@kopf.on.create('ephemeralvolumeclaims')
def create_fn(spec, name, namespace, logger, **kwargs):

    size = spec.get('size')
    if not size:
        raise kopf.PermanentError(f"Size must be set. Got {size!r}.")

    path = os.path.join(os.path.dirname(__file__), 'pvc.yaml')
    tmpl = open(path, 'rt').read()
    text = tmpl.format(size=size, name=name)
    data = yaml.safe_load(text)

    api = kubernetes.client.CoreV1Api()
    obj = api.create_namespaced_persistent_volume_claim(
        namespace=namespace,
        body=data,
    )

    logger.info(f"PVC child is created: {obj}")

    return {'pvc-name': obj.metadata.name}

Whatever is returned from any handler, is stored in the object’s status under that handler id (which is the function name by default). We can see that with kubectl:

kubectl get -o yaml evc my-claim

spec:
  size: 1G
status:
  create_fn:
    pvc-name: my-claim
  kopf: {}

Note

If the above change causes Patching failed with inconsistencies debug warnings and/or your EVC YAML doesn’t show a .status field, make sure you have set the x-kubernetes-preserve-unknown-fields: true field in your CRD on either the entire object or just the .status field as detailed in Custom Resources. Without setting this field, Kubernetes will prune the .status field when Kopf tries to update it. For more info on field pruning, see the Kubernetes docs.

Let’s add a yet another handler, but for the “update” cause. This handler gets this stored PVC name from the creation handler, and patches the PVC with the new size from the EVC:

@kopf.on.update('ephemeralvolumeclaims')
def update_fn(spec, status, namespace, logger, **kwargs):

    size = spec.get('size', None)
    if not size:
        raise kopf.PermanentError(f"Size must be set. Got {size!r}.")

    pvc_name = status['create_fn']['pvc-name']
    pvc_patch = {'spec': {'resources': {'requests': {'storage': size}}}}

    api = kubernetes.client.CoreV1Api()
    obj = api.patch_namespaced_persistent_volume_claim(
        namespace=namespace,
        name=pvc_name,
        body=pvc_patch,
    )

    logger.info(f"PVC child is updated: {obj}")

Now, let’s change the EVC’s size:

kubectl edit evc my-claim

Or by patching it:

kubectl patch evc my-claim --type merge -p '{"spec": {"size": "2G"}}'

Keep in mind the PVC size can only be increased, never decreased.

Give the operator a few seconds to handle the change.

Check the size of the actual PV behind the PVC, which is now increased:

kubectl get pv

NAME                                       CAPACITY   ACCESS MODES   ...
pvc-a37b65bd-8384-11e9-b857-42010a800265   2Gi        RWO            ...

Warning

Kubernetes & kubectl improperly show the capacity of PVCs: it remains the same (1G) event after the change. The size of the actual PV (Persistent Volume) of each PVC is important! This issue is not related to Kopf, so we go around it.