State Persistence

Updated Dec 29, 2023 ·

Some of the scenario questions here are based on Kodekloud's CKAD course labs.

NOTE

CKAD and CKA can have similar scenario questions. It is recommended to go through the CKA practice tests.

Shortcuts

First run the two commands below for shortcuts.

export do="--dry-run=client -o yaml" 
export now="--force --grace-period=0" 

Questions

Configure a volume to store the webapp logs (stored at /log/app.log) at /var/log/webapp on the host. Use the spec provided below.

Name: webapp
Image Name: kodekloud/event-simulator
Volume HostPath: /var/log/webapp
Volume Mount: /log

Answer

controlplane ~ ➜  k get po
NAME     READY   STATUS    RESTARTS   AGE
webapp   1/1     Running   0          48s

controlplane ~ ➜  k exec -it webapp -- cat /log/app.log
[2023-12-30 11:51:39,293] INFO in event-simulator: USER3 is viewing page3
[2023-12-30 11:51:40,294] INFO in event-simulator: USER3 is viewing page3
[2023-12-30 11:51:41,295] INFO in event-simulator: USER3 is viewing page3
[2023-12-30 11:51:42,296] INFO in event-simulator: USER1 is viewing page1
[2023-12-30 11:51:43,297] INFO in event-simulator: USER1 is viewing page2
[2023-12-30 11:51:44,298] WARNING in event-simulator: USER5 Failed to Login as the account is locked due to MANY FAILED ATTEMPTS. 

Generate a YAML file first and then delete the pod.

controlplane ~ ➜  k get po
NAME     READY   STATUS    RESTARTS   AGE
webapp   1/1     Running   0          4m54s

controlplane ~ ➜  k get po webapp -o yaml > webapp.yml

controlplane ~ ➜  ls -l
total 4
-rw-rw-rw- 1 root root    0 Dec 13 05:39 sample.yaml
-rw-r--r-- 1 root root 2658 Dec 30 06:56 webapp.yml

controlplane ~ ➜  k delete po webapp $now
Warning: Immediate deletion does not wait for confirmation that the running resource has been terminated. The resource may continue to run on the cluster indefinitely.
pod "webapp" force deleted

controlplane ~ ➜  k get po
No resources found in default namespace.  

Add the volume and volumemount in the YAML file. Follow K8S docs.

## webapp.yml 
apiVersion: v1
kind: Pod
metadata:
  name: webapp
spec:
  containers:
  - name: event-simulator
    image: kodekloud/event-simulator
    env:
    - name: LOG_HANDLERS
      value: file
    volumeMounts:
    - mountPath: /log
      name: log-volume

  volumes:
  - name: log-volume
    hostPath:
    # directory location on host
      path: /var/log/webapp
    # this field is optional
      type: Directory

controlplane ~ ➜  k apply -f webapp.yml 
pod/webapp created

controlplane ~ ➜  k get po
NAME     READY   STATUS    RESTARTS   AGE
webapp   1/1     Running   0          3s 

Create a Persistent Volume with the given specification.

Volume Name: pv-log
Storage: 100Mi
Access Modes: ReadWriteMany
Host Path: /pv/log
Reclaim Policy: Retain

Answer

## pv-log.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-log
spec:
  persistentVolumeReclaimPolicy: Retain
  accessModes:
    - ReadWriteMany
  capacity:
    storage: 100Mi
  storageClassName: ""
  hostPath:
    path: /pv/log

controlplane ~ ➜  k apply -f pv-log.yaml 
persistentvolume/pv-log created

controlplane ~ ➜  k get pv
NAME     CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM   STORAGECLASS   REASON   AGE
pv-log   100Mi      RWX            Retain           Available                                   2s 

Create a Persistent Volume Claim with the given specification.

Volume Name: claim-log-1
Storage Request: 50Mi
Access Modes: ReadWriteMany

Answer

## pvc-log.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: claim-log-1
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 50Mi

controlplane ~ ➜  k apply -f pvc-log.yaml 
persistentvolumeclaim/claim-log-1 created

controlplane ~ ➜  k get pv
NAME     CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                 STORAGECLASS   REASON   AGE
pv-log   100Mi      RWX            Retain           Bound    default/claim-log-1                           4m9s

controlplane ~ ➜  k get pvc
NAME          STATUS   VOLUME   CAPACITY   ACCESS MODES   STORAGECLASS   AGE
claim-log-1   Bound    pv-log   100Mi      RWX                           11s 

What is the Volume Binding Mode used for this storage class local-storage?

controlplane ~ ➜  k get sc
NAME                        PROVISIONER                     RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
local-path (default)        rancher.io/local-path           Delete          WaitForFirstConsumer   false                  9m44s
local-storage               kubernetes.io/no-provisioner    Delete          WaitForFirstConsumer   false                  36s
portworx-io-priority-high   kubernetes.io/portworx-volume   Delete          Immediate              false                  36s 

Answer

controlplane ~ ✖ k describe sc local-storage 
Name:            local-storage
IsDefaultClass:  No
Annotations:     kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"storage.k8s.io/v1","kind":"StorageClass","metadata":{"annotations":{},"name":"local-storage"},"provisioner":"kubernetes.io/no-provisioner","volumeBindingMode":"WaitForFirstConsumer"}

Provisioner:           kubernetes.io/no-provisioner
Parameters:            <none>
AllowVolumeExpansion:  <unset>
MountOptions:          <none>
ReclaimPolicy:         Delete
VolumeBindingMode:     WaitForFirstConsumer
Events:                <none> 

Create a new PersistentVolumeClaim by the name of local-pvc that should bind to the volume local-pv.

PVC: local-pvc
Correct Access Mode?
Correct StorageClass Used?
PVC requests volume size = 500Mi?

Answer

controlplane ~ ➜  k get pv
NAME       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM   STORAGECLASS    REASON   AGE
local-pv   500Mi      RWO            Retain           Available           local-storage            19m 

controlplane ~ ➜  k describe pv local-pv 
Name:              local-pv
Labels:            <none>
Annotations:       <none>
Finalizers:        [kubernetes.io/pv-protection]
StorageClass:      local-storage
Status:            Available
Claim:             
Reclaim Policy:    Retain
Access Modes:      RWO
VolumeMode:        Filesystem
Capacity:          500Mi
Node Affinity:     
Required Terms:  
    Term 0:        kubernetes.io/hostname in [controlplane]
Message:           
Source:
    Type:  LocalVolume (a persistent volume backed by local storage on a node)
    Path:  /opt/vol1
Events:    <none>

## local-pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: local-pvc
spec:
  accessModes:
    - ReadWriteOnce
  volumeMode: Filesystem
  storageClassName: local-storage
  resources:
    requests:
      storage: 500Mi 

controlplane ~ ➜  k apply -f local-pvc.yaml 
persistentvolumeclaim/local-pvc created 

Create a new pod called nginx with the image nginx:alpine. The Pod should make use of the PVC local-pvc and mount the volume at the path /var/www/html. The PV local-pv should be in a bound state.

controlplane ~ ➜  k get pv
NAME       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM   STORAGECLASS    REASON   AGE
local-pv   500Mi      RWO            Retain           Available           local-storage            29m

controlplane ~ ➜  k get pvc
NAME        STATUS    VOLUME   CAPACITY   ACCESS MODES   STORAGECLASS    AGE
local-pvc   Pending                                      local-storage   5m17s 

Answer

controlplane ~ ➜  export do="--dry-run=client -o yaml"

controlplane ~ ➜  export now="--force --grace-period 0" 

controlplane ~ ➜  k run nginx --image nginx:alpine $do > nginx.yaml

## nginx.yaml
apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: nginx
  name: nginx
spec:
  containers:
  - image: nginx:alpine
    name: nginx
    resources: {}
    volumeMounts:
    - mountPath: "/var/www/html"
      name: local-pv
  volumes:
  - name: local-pv
    persistentVolumeClaim:
        claimName: local-pvc
status: {} 

controlplane ~ ➜  k apply -f nginx.yaml 
pod/nginx created

controlplane ~ ➜  k get po
NAME    READY   STATUS    RESTARTS   AGE
nginx   1/1     Running   0          6s

controlplane ~ ➜  k get pv
NAME       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM               STORAGECLASS    REASON   AGE
local-pv   500Mi      RWO            Retain           Bound    default/local-pvc   local-storage            31m

controlplane ~ ➜  k get pvc
NAME        STATUS   VOLUME     CAPACITY   ACCESS MODES   STORAGECLASS    AGE
local-pvc   Bound    local-pv   500Mi      RWO            local-storage   7m16s 

Create a new Storage Class called delayed-volume-sc that makes use of the below specs:

provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer

Answer

## delayed-volume-sc.yaml 
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: delayed-volume-sc
  annotations:
    storageclass.kubernetes.io/is-default-class: "false"
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer 

controlplane ~ ➜  k apply -f delayed-volume-sc.yaml 
storageclass.storage.k8s.io/delayed-volume-sc created

controlplane ~ ➜  k get sc
NAME                        PROVISIONER                     RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
local-path (default)        rancher.io/local-path           Delete          WaitForFirstConsumer   false                  45m
local-storage               kubernetes.io/no-provisioner    Delete          WaitForFirstConsumer   false                  35m
portworx-io-priority-high   kubernetes.io/portworx-volume   Delete          Immediate              false                  35m
delayed-volume-sc           kubernetes.io/no-provisioner    Delete          WaitForFirstConsumer   false                  3s 

Shortcuts​

Questions​

Shortcuts

Questions