In Kubernetes and in docker in general, there are several type of storage, but let's focus on the basics here:

• Dynamic
• Static

To better illustrate this, check the following pictures:

Now, let's discuss a little bit about the components here. We will start from left to right.

• Storage

First you have the actual storage, that storage can be cloud (AWS, Google, IBM Cloud etc) or Local (iSCSI, NAS, SAN, bare metal, etc). Kubernetes has a lot of plugins to provide access to that storage. On the other side, that storage can be replicated, hashed, mapped, encrypted, in RAID and so on and so on. From Kubernetes point of view, it is seen simply as a storage thanks to the plugin

• Plugin

Plugins provide the entry point for Kubernetes, as described above, there are different plugins, like EBS Plugin for Cloud Volume or local for local storage. You can check more about Kubernetes Plugins here.

• Persistent Volume (PV)

Persistent Volume represent the volumes in Kubernetes term, in other words, the physical representation of the volume gets translated to persistent volume in kubernetes terms. To use that volume, of course we have to use the next component, which is:

• Persistent Volume Claim (PVC)

Both, PV and PVC are first class objects in Kubernetes, which means, that just like we can GET and DESCRIBE Pods, we can do the same for PV/PVC. It is important to note, that once a PVC has connected to PV, other PVC cannot connect to the same PV.

• Volume

Lastly, we have the Volumes, which are the PV in the POD. Once the Volume is linked with the PVC which is linked with the PV. That PV can be used only by the containers which are in that pod. Other pods or other containers outside of the pod, cannot use that storage.

So, in a nutshell:

1. We define the storage
2. We define the PV
3. We define the PVC
4. Lastly, we define the Volume in the pod configuration.

There is a BIG issue with that kinda provisioning, IT DOESN'T SCALE. because of that, we have two type of privisioning:

• Static
• Dynamic

So let's get going and see how it is done with each type:

Let's configure Static storage.

Firstly, as we said, we have to configure, the PV, let's take one example of a PV:

kind: PersistentVolume
apiVersion: v1                                 <- It is first Class object, just like Pod, Deployment and so on
metadata:
  name: ps-pv                                  <- The name is completely arbitrary, so choose whatever, but with reason :)
  labels:
    type: local                                <- Local Label
spec:
  storageClassName: ps-fast                    <- Indicate that it is in "ps-fast" storage Class
  capacity:
    storage: 10Gi                              <- We allocate 10 GBs
  persistentVolumeReclaimPolicy: Retain        <- What to happen after you remove a PVC?
#Retain - Keep it in "protected" mode
#Delete(Default) - This will DELETE the PV after removing the PVC
  accessModes:
    - ReadWriteOnce           
#         ^
#         |
#There are 3 access modes: 
#ReadWriteOnce - The PV can be taken in RW once by one pod
#ReadWriteMany - Same as above just it can be taken lots of times.
#ReadOnlyMany - RO for a lot of PODs. Not all type support all 3 modes
#For example, block devices don't support ReadWriteMany, but File based volumes (NFS, Object Volumes) usually do. Check your plugin docks
  hostPath:
    path: "/home/ubuntu/volume1"

You can see the description for each important attritube above. So that covers the explanation :)

Let's configure Dynamic storage.