Persistent Volume Claims

Persistent Volume Claims add storage to a node.
Persistent Volumes and Persistent Volume Claims are two separate objects in the Kubernetes namespace.
An Administrator creates Persistent Volumes and a user makes the Persistent Volume Claims.
Once created, Kubernetes binds the set Persistent Volume and its Persistent Volume Claim together.
Kubernetes tries to find a Persistent Volume, that has the right capacity asked for by the claim.
- Kubernetes looks for the following:
  - Sufficient Capacity
  - Access Modes
  - Volume Modes
  - Storage Class
If there are multiple Persistent Volume Claims aimed at one Persistent Volume, then you can use labels and selectors for that. For example with a Persistent Volume:
```
labels:
name: my-pw
```
For the Persistent Volume Claim:
```
selector:
matchLabels:
  name: my-pv
```
A smaller Persistent Volume Claim, may be bound to a larger Persistent Volume, if there are no better options available.
There is a 1:1 relationship with Persistent Volumes and Persistent Volume Claims, so even if there is leftover space on a Persistent Volume, no other Persistent Volume Claims can use it.
If there are no other Persistent Volumes available and a Persistent Volume Claim is looking for a Persistent Volume to bind with, that Persistent Volume Claim will go into a Pending state.
- When newer Persistent Volumes are available, the Persistent Volume Claim can then be bound successfully.
Example Persistent Volume Claim of pvc-definition.yaml: ``` apiVersion: v1 kind: PersistentVolumeClaim metdata: name: myclaim spec: accessModes:
- ReadWriteOnce resources: requests: storage: 500Mi ```
Create the Persistent Volume Claim definition file with this command:
```
kubectl create -f pvc-definition.yaml
```
Check the Persistent Volume Claims with:
```
kubectl get persistentvolumeclaim
```
When a PVC is created, Kubernetes looks at the volume that was made previously.

Previously the following Persistent Volume was made available. Pairing this with the Persistent Volume Claim above will allow it to be bound (albeit wasting 500MB of storage).

apiVersion: v1
kind: PersistentVolume
metadata:
 name: pv-vol1
spec:
accessModes:
    - ReadWriteOnce
capacity:
    storage: 1Gi
awsElasticBlockStore:
  volumeID: <volume-id>
  fsType: ext4

Running the kubectl get persistentvolumeclaim command again shows the following:

Name	STATUS	VOLUME	CAPACITY	ACCESS MODES	STORAGECLASS	AGE
myclaim	Bound	pv-vol1	1Gi			RWO			43m

To delete a PVC, run the following:

kubectl delete persistentvolumeclaim myclaim

What happens to the underlying Persistent Volume when the claim is deleted?
- By default, the persistentVolumeReclaimPolicy is set to Retain
- persistentVolume will remain until it is manually deleted.
- Not available for reuse by any other claims!
Else it can be deleted with the following:
```
persistentVolumeReclaimPolicy: Delete
```
The above deletes the Persistent Volume Claim automatically.
A third option is:
```
persistentVolumeReclaimPolicy: Recycle
```
For the above, the data in the data volume will be scrubbed, before it is available to other claims.