State Persistence

Updated Dec 29, 2023 · 2 min read

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

1. 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 

2. 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 

3. 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 

4. 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> 

5. 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 

6. 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 

7. 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