We've learned about Volumes in Chapter 2, Walking through Kubernetes Concepts. We know PersistentVolumeClaims is used to abstract storage resources from users. It can dynamically provision the PersistentVolume via StorageClass. The default provisioner in StorageClass in AWS CloudProvider is Elastic Block Storage Service‎ (aws-ebs). Whenever you request a PVC, aws-ebs provisioner will create a volume in AWS EBS.

Let's check the storage class in our cluster:

// list all storageclass
# kubectl get storageclass
NAME            PROVISIONER             AGE
default         kubernetes.io/aws-ebs   2h
gp2 (default)   kubernetes.io/aws-ebs   2h
In this recipe, we'll reuse the PVC example we mentioned in Chapter 2-6:
# cat chapter2/2-6_volumes/2-6-7_pvc.yaml
apiVersion: "v1"
kind: "PersistentVolumeClaim"
metadata:
  name: "pvclaim01"
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
// create pvc
# kubectl create -f chapter2/2-6_volumes/2-6-7_pvc.yaml
persistentvolumeclaim "pvclaim01" created
// check pvc is created successfully.
# kubectl get pvc
NAME        STATUS    VOLUME                                     CAPACITY   
pvclaim01   Bound     pvc-e3d881d4-402e-11e8-b124-0ef0c7f25d36   1Gi        
ACCESS    MODES   STORAGECLASS   AGE
RWO            gp2            16m

After PVC is created, an associated PV will be created:

# kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   
pvc-e3d881d4-402e-11e8-b124-0ef0c7f25d36   1Gi        RWO
RECLAIM POLICY   STATUS    CLAIM               STORAGECLASS   REASON    AGE
Delete           Bound     default/pvclaim01   gp2                      16m

You can take a closer look at PV here:

# kubectl describe pv pvc-e3d881d4-402e-11e8-b124-0ef0c7f25d36
Name:            pvc-e3d881d4-402e-11e8-b124-0ef0c7f25d36
Labels:          failure-domain.beta.kubernetes.io/region=us-east-1
                 failure-domain.beta.kubernetes.io/zone=us-east-1a
Annotations:     kubernetes.io/createdby=aws-ebs-dynamic-provisioner
                 pv.kubernetes.io/bound-by-controller=yes
                 pv.kubernetes.io/provisioned-by=kubernetes.io/aws-ebs
Claim:           default/pvclaim01
...
Source:
    Type:       AWSElasticBlockStore (a Persistent Disk resource in AWS)
    VolumeID:   aws://us-east-1a/vol-035ca31b9cc1820d7
    FSType:     ext4
    Partition:  0
    ReadOnly:   false

We can find that it's associated with the claim we just created pvclaim01 and the source type is AWSElasticBlockStore, as expected.

We can use AWS CLI to inspect the volume we created in EBS. Using the --filter Name=tag-value we can filter the volumes in EBS:

// aws ec2 describe-volumes --filter Name=tag-value,Values=$PV_NAME
# aws ec2 describe-volumes --filter Name=tag-value,Values="pvc-e3d881d4-402e-11e8-b124-0ef0c7f25d36"{
    "Volumes": [
        {
            "AvailabilityZone": "us-east-1a",
             "Tags": [
                {   "Value": "k8s-cookbook.net",
                    "Key": "KubernetesCluster" },
                {   "Value": "default",
                    "Key": "kubernetes.io/created-for/pvc/namespace" },
                {   "Value": "k8s-cookbook.net-dynamic-pvc-e3d881d4-402e-11e8-b124-0ef0c7f25d36",
                    "Key": "Name" },
                {   "Value": "pvclaim01",
                    "Key": "kubernetes.io/created-for/pvc/name" },
                {   "Value": "owned",
                    "Key": "kubernetes.io/cluster/k8s-cookbook.net" },
                {   "Value": "pvc-e3d881d4-402e-11e8-b124-0ef0c7f25d36",
                    "Key": "kubernetes.io/created-for/pv/name" }],
            "VolumeType": "gp2",
            "VolumeId": "vol-035ca31b9cc1820d7",
         ...
        }    
   ]
}

We can see that the EBS resource has been tagged with lots of different values: by observing these tags, we can know which Kubernetes cluster, namespace, PVC, and PV are associated with this EBS volume.

Thanks to dynamic provisioning that StorageClass and CloudProvider support, Volume management is no longer a huge pain. We can create and destroy PV on the fly.