Kubernetes Volumes

Persistent Volume (PV) and Persistent Volume Claim (PVC)

References:

https://www.youtube.com/watch?v=OulmwTYTauI&ab_channel=SeanWingert

Persistent Volume Claim (PVC)

• Claims a certain amount of volume for the designated pods

  • More than one pod can map back to one PVC - so multiple pods can share one storage space if needed

• Does not need to specify where the storage is coming from (Cloud, SSD, etc.), only concerned with how much storage is needed for the pods

  • Since these are supposed to be written up by the developers, the developers don't need to know where the storage is coming from, they just need storage

• PVC binds with either a Persistent Volume or a Storage Class

Persistent Volume (PV)

• Specifies where the volumes are coming from (Cloud, SSD, etc.)

• Acts as an abstraction to physical storage

• Ops people are meant to handle this

Note: Cannot bind 2 PVCs to the same PV, but can bind 2 PVs to the same PVC

Example

https://gitlab.com/nanuchi/youtube-tutorial-series/-/blob/master/configmap-and-secret-volumes/mosquitto-config-components.yaml (View comments in the following example to understand better)

random note: commenting out doesn't seem to work that often so be careful in case you see your volume is not mounting for some reason and there are no errors being thrown

apiVersion: v1
kind: ConfigMap
metadata:
  name: mosquitto-config-file
data:
  mosquitto.conf: |
    log_dest stdout
    log_type all
    log_timestamp true
    listener 9001

---
apiVersion: v1
kind: Secret
metadata:
  name: mosquitto-secret-file
type: Opaque
data:
  secret.file: |
    c29tZXN1cGVyc2VjcmV0IGZpbGUgY29udGVudHMgbm9ib2R5IHNob3VsZCBzZWU=

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: mosquitto
  labels:
    app: mosquitto
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mosquitto
  template:
    metadata:
      labels:
        app: mosquitto
    spec:
      containers: 
        - name: mosquitto
          image: eclipse-mosquitto:1.6.2
          ports:
            - containerPort: 1883
          volumeMounts: # Here, we list all volumes we want to mount from POD TO CONTAINER
            - name: mosquitto-conf # Notice this obviously must exist in the POD (look below)
              mountPath: /mosquitto/config # Path in the filesystem inside the container 
            - name: mosquitto-secret
              mountPath: /mosquitto/secret  
              readOnly: true
      volumes: # Here, we list all volumes we want to mount in the POD
        - name: mosquitto-conf
          configMap:
            name: mosquitto-config-file # Name of the ConfigMap resource (look above)
        - name: mosquitto-secret 
          secret:
            secretName: mosquitto-secret-file # Name of the Secret resource (look above)

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: mosquitto
  labels:
    app: mosquitto
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mosquitto
  template:
    metadata:
      labels:
        app: mosquitto
    spec:
      containers:
        - name: mosquitto
          image: eclipse-mosquitto:1.6.2
          ports:
            - containerPort: 1883