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Akshay Rao
Akshay Rao

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K8s Exercise: Persistent State

#kubernetes #devops #beginners

Introduction
Hi, I am Akshay Rao, will be starting a exercise series on k8s.
In this blog there will not explanation only problems and solutions.if you want explanation have a look at this series:-
https://dev.to/aksrao1998/series/24887

Pre-requisite
have minikube or kind running in the local machine.

Note:- k is alias for kubectl.

Let's Start

Problem 1
Create busybox pod with two containers, each one will have the image busybox and will run the 'sleep 3600' command. Make both containers mount an emptyDir at '/etc/foo'. Connect to the second busybox, write the first column of '/etc/passwd' file to '/etc/foo/passwd'. Connect to the first busybox and write '/etc/foo/passwd' file to standard output. Delete pod.

Solution

[k8s-ckad (⎈|minikube:mynamespace)]$ k run busybox --image=busybox --dry-run=client -o yaml > pod2.yaml #edit the pod2.yaml apiVersion: v1 kind: Pod metadata: creationTimestamp: null labels: run: busybox name: busybox spec: dnsPolicy: ClusterFirst restartPolicy: Never containers: - image: busybox name: busybox0 command: ["/bin/sh","-c","sleep 3600"] volumeMounts: - mountPath: /etc/foo name: anyvolume resources: {} - image: busybox name: busybox1 command: ["/bin/sh","-c","sleep 3600"] volumeMounts: - mountPath: /etc/foo name: anyvolume resources: {} dnsPolicy: ClusterFirst restartPolicy: Always volumes: - name: anyvolume emptyDir: {} status: {} [k8s-ckad (⎈|minikube:mynamespace)]$ k create -f pod2.yaml pod/busybox created # login in container [k8s-ckad (⎈|minikube:mynamespace)]$ k exec -it busybox -c busybox0 -- /bin/sh /etc # cd /etc/foo/ /etc/foo # ls /etc/foo # cat /etc/passwd root:x:0:0:root:/root:/bin/sh daemon:x:1:1:daemon:/usr/sbin:/bin/false bin:x:2:2:bin:/bin:/bin/false sys:x:3:3:sys:/dev:/bin/false sync:x:4:100:sync:/bin:/bin/sync mail:x:8:8:mail:/var/spool/mail:/bin/false www-data:x:33:33:www-data:/var/www:/bin/false operator:x:37:37:Operator:/var:/bin/false nobody:x:65534:65534:nobody:/home:/bin/false /etc/foo # cat /etc/passwd | awk '{print $1}' > /etc/foo/passwd /etc/foo # ls passwd /etc/foo # cat passwd root:x:0:0:root:/root:/bin/sh daemon:x:1:1:daemon:/usr/sbin:/bin/false bin:x:2:2:bin:/bin:/bin/false sys:x:3:3:sys:/dev:/bin/false sync:x:4:100:sync:/bin:/bin/sync mail:x:8:8:mail:/var/spool/mail:/bin/false www-data:x:33:33:www-data:/var/www:/bin/false operator:x:37:37:Operator:/var:/bin/false nobody:x:65534:65534:nobody:/home:/bin/false /etc/foo # # verify this is updated in the other container automatically [k8s-ckad (⎈|minikube:mynamespace)]$ k exec -it busybox -c busybox1 -- /bin/sh / # / # cat /etc/foo/passwd root:x:0:0:root:/root:/bin/sh daemon:x:1:1:daemon:/usr/sbin:/bin/false bin:x:2:2:bin:/bin:/bin/false sys:x:3:3:sys:/dev:/bin/false sync:x:4:100:sync:/bin:/bin/sync mail:x:8:8:mail:/var/spool/mail:/bin/false www-data:x:33:33:www-data:/var/www:/bin/false operator:x:37:37:Operator:/var:/bin/false nobody:x:65534:65534:nobody:/home:/bin/false
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Problem 2
Create a PersistentVolume of 10Gi, called 'myvolume'. Make it have accessMode of 'ReadWriteOnce' and 'ReadWriteMany', storageClassName 'normal', mounted on hostPath '/etc/foo'. Save it on pv.yaml, add it to the cluster. Show the PersistentVolumes that exist on the cluster.

Solution

# create a file name pv.yaml apiVersion: v1 kind: PersistentVolume metadata: name: myvolume spec: capacity: storage: 10Gi accessModes: - ReadWriteOnce - ReadWriteMany persistentVolumeReclaimPolicy: Recycle storageClassName: normal hostPath: path: /etc/foo # verify [k8s-ckad (⎈|minikube:mynamespace)]$ k get pv NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE myvolume 10Gi RWO,RWX Recycle Available normal 32s
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Problem 3
Create a PersistentVolumeClaim for this storage class, called 'mypvc', a request of 4Gi and an accessMode of ReadWriteOnce, with the storageClassName of normal, and save it on pvc.yaml. Create it on the cluster. Show the PersistentVolumeClaims of the cluster.

Solution

# create a pvc.yaml file apiVersion: v1 kind: PersistentVolumeClaim metadata: name: mypvc spec: accessModes: - ReadWriteOnce resources: requests: storage: 4Gi storageClassName: normal # verify [k8s-ckad (⎈|minikube:mynamespace)]$ k create -f pvc.yaml persistentvolumeclaim/mypvc created [k8s-ckad (⎈|minikube:mynamespace)]$ k get pvc NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE mypvc Bound myvolume 10Gi RWO,RWX normal 5s
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Problem 3

  • Create a busybox pod with command 'sleep 3600', save it on pod.yaml. Mount the PersistentVolumeClaim to '/etc/foo'. Connect to the 'busybox' pod, and copy the '/etc/passwd' file to '/etc/foo/passwd'.
  • Create a second pod which is identical with the one you just created (you can easily do it by changing the 'name' property on pod.yaml). Connect to it and verify that '/etc/foo' contains the 'passwd' file. Delete pods to cleanup. Note: If you can't see the file from the second pod, can you figure out why? What would you do to fix that?

Solution

Part-1 apiVersion: v1 kind: Pod metadata: creationTimestamp: null labels: run: busybox name: busybox spec: dnsPolicy: ClusterFirst restartPolicy: Never containers: - image: busybox name: busybox0 command: ["/bin/sh","-c","sleep 3600"] volumeMounts: - mountPath: /etc/foo name: anyvolume resources: {} dnsPolicy: ClusterFirst restartPolicy: Always volumes: - name: anyvolume persistentVolumeClaim: claimName: mypvc status: {} [k8s-ckad (⎈|minikube:mynamespace)]$ k create -f pod.yaml pod/busybox created Copy the passwd file [k8s-ckad (⎈|minikube:mynamespace)]$ k exec -it busybox -- /bin/sh / # cp /etc/passwd /etc/foo/ / # ls /etc/foo passwd Part-2 # change the labels to busybox1 apiVersion: v1 kind: Pod metadata: creationTimestamp: null labels: run: busybo1 name: busybox1 spec: dnsPolicy: ClusterFirst restartPolicy: Never containers: - image: busybox name: busybox1 command: ["/bin/sh","-c","sleep 3600"] volumeMounts: - mountPath: /etc/foo name: anyvolume resources: {} dnsPolicy: ClusterFirst restartPolicy: Always volumes: - name: anyvolume persistentVolumeClaim: claimName: mypvc status: {} [k8s-ckad (⎈|minikube:mynamespace)]$ k create -f pod3.yaml pod/busybox1 created #verify [k8s-ckad (⎈|minikube:mynamespace)]$ k exec -it busybox1 -- /bin/sh / # / # ls /etc/foo passwd / # # delete the resources [k8s-ckad (⎈|minikube:mynamespace)]$ k delete po busybox pod "busybox" deleted [k8s-ckad (⎈|minikube:mynamespace)]$ k delete po busybox1 pod "busybox1" deleted [k8s-ckad (⎈|minikube:mynamespace)]$ k delete pv myvolume persistentvolume "myvolume" deleted [k8s-ckad (⎈|minikube:mynamespace)]$ k delete pvc mypvc persistentvolumeclaim "mypvc" deleted
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