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15.UsingPersistentStorage.adoc

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Using Persistent Storage

Prerequisites

  • You have access to OpenShift Web Console URL. Ask your workshop coordinator for URL if you don’t have one.

  • You have credentials to login. Ask your workshop coordinator for credentials to log onto the OpenShift cluster

Introduction

With OpenShift files that live on the container instance are ephemeral. This means that once the pod is destroyed or reinstantiated any changes to the files or data storage on the container is destoryed.

PersistentVolume (PV) is an API object, which represents a piece of existing storage in the cluster that was either statically provisioned by the cluster administrator or dynamically provisioned using a StorageClass object. It is a resource in the cluster just like a node is a cluster resource.

Types of PVs

OpenShift Container Platform supports the following PersistentVolume plug-ins:

  • AWS Elastic Block Store (EBS)

  • Azure Disk

  • Azure File

  • Cinder

  • Fibre Channel

  • GCE Persistent Disk

  • HostPath

  • iSCSI

  • Local volume

  • NFS

  • Red Hat OpenShift Container Storage

  • VMware vSphere

Table 1. Supported access modes for PVs
Volume Plug-in ReadWriteOnce ReadOnlyMany ReadWriteMany

AWS EBS

[*]

[ ]

[ ]

Azure File

[*]

[ *]

[* ]

Azure Disk

[*]

[ ]

[ ]

Cinder

[*]

[ ]

[ ]

Fibre Channel

[*]

[*]

[ ]

GCE Persistent Disk

[*]

[ ]

[ ]

HostPath

[*]

[ ]

[ ]

iSCSI

[*]

[*]

[ ]

Local volume

[*]

[ ]

[ ]

NFS

[*]

[*]

[*]

Red Hat OpenShift Container Storage

[*]

[ ]

[*]

vSphere

[*]

[ ]

[ ]

PersistentVolumeClaim is an API Object, which represents a request for storage by a developer. It is similar to a Pod in that Pods consume node resources and PVCs consume PV resources. A PVC provides an abstraction layer to underlying storage. An administrator could create a number of static persistent volumes (PVs) that can later be bound to one or more persistent volume claims.

Exercise

Prepare Exercise

  • Login to OpenShift

  • Create new project

$ oc new-project pvc-demo-userXX
Note
 Change userXX to your username provided by your workshop coordinator.

Create a Persistent Volume Claim

  • Create a pv definition file.

cat >myclaim-userXX-pvc.yml<<EOF
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: myclaim-userXX
  namespace: pvc-demo-userXX-userXX
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi
EOF

  • Create the persistent volume claim.

oc create -f myclaim-userXX-pvc.yml

  • Get pvc status*

oc get pvc

  • Mount your pv to a pod by deploying sample app

cat >deploy-pvc.yml<<EOF
apiVersion: apps/v1
kind: Deployment
metadata:
  name: pv-deploy
  labels:
    app: mypv
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mypv
  template:
    metadata:
      labels:
        app: mypv
    spec:
      containers:
      - name: shell
        image: centos:7
        command:
        - "bin/bash"
        - "-c"
        - "sleep 10000"
        volumeMounts:
        - name: mypd
          mountPath: "/tmp/persistent"
      volumes:
      - name: mypd
        persistentVolumeClaim:
          claimName: myclaim-userXX
EOF

  • Deploy app

$ oc create -f deploy-pvc.yml
deployment.apps/pv-deploy created

  • Get pod name

$ oc get pods
NAME                        READY   STATUS    RESTARTS   AGE
pv-deploy-f8d4f87f6-mlspk   1/1     Running   0          2m26s

  • Review pod configuration

$ oc describe pod pv-deploy-f8d4f87f6-mlspk
Name:         pv-deploy-f8d4f87f6-mlspk
Namespace:    pvc-demo-userXX
Priority:     0
Node:         ip-10-0-159-218.us-east-2.compute.internal/10.0.159.218
Start Time:   Fri, 31 Jan 2020 17:22:18 +0000
Labels:       app=mypv
              pod-template-hash=f8d4f87f6
Annotations:  k8s.v1.cni.cncf.io/networks-status:
                [{
                    "name": "openshift-sdn",
                    "interface": "eth0",
                    "ips": [
                        "10.128.2.16"
                    ],
                    "dns": {},
                    "default-route": [
                        "10.128.2.1"
                    ]
                }]
              openshift.io/scc: restricted
Status:       Running
IP:           10.128.2.16
IPs:
  IP:           10.128.2.16
Controlled By:  ReplicaSet/pv-deploy-f8d4f87f6
Containers:
  shell:
    Container ID:  cri-o://c3ec65f4b7af095310cf62e40dc35c0ddef021e968c63fc99ae13cf78b02fe5d
    Image:         centos:7
    Image ID:      docker.io/library/centos@sha256:285bc3161133ec01d8ca8680cd746eecbfdbc1faa6313bd863151c4b26d7e5a5
    Port:          <none>
    Host Port:     <none>
    Command:
      bin/bash
      -c
      sleep 10000
    State:          Running
      Started:      Fri, 31 Jan 2020 17:22:32 +0000
    Ready:          True
    Restart Count:  0
    Environment:    <none>
    Mounts:
      /tmp/persistent from mypd (rw)
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-27rcv (ro)
Conditions:
  Type              Status
  Initialized       True
  Ready             True
  ContainersReady   True
  PodScheduled      True
Volumes:
  mypd:
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  myclaim-userXX
    ReadOnly:   false
  default-token-27rcv:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-27rcv
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
                 node.kubernetes.io/unreachable:NoExecute for 300s
Events:
  Type    Reason                  Age        From                                                 Message
  ----    ------                  ----       ----                                                 -------
  Normal  Scheduled               <unknown>  default-scheduler                                    Successfully assigned pvc-demo-userXX/pv-deploy-f8d4f87f6-mlspk to ip-10-0-159-218.us-east-2.compute.internal
  Normal  SuccessfulAttachVolume  3m19s      attachdetach-controller                              AttachVolume.Attach succeeded for volume "pvc-a4a724b1-b711-40a1-a7c9-f89b7db209c7"
  Normal  Pulled                  3m9s       kubelet, ip-10-0-159-218.us-east-2.compute.internal  Container image "centos:7" already present on machine
  Normal  Created                 3m8s       kubelet, ip-10-0-159-218.us-east-2.compute.internal  Created container shell
  Normal  Started                 3m8s       kubelet, ip-10-0-159-218.us-east-2.compute.internal  Started container shell

  • test mount

$ oc exec -i -t  pv-deploy-f8d4f87f6-mlspk  /bin/bash
bash-4.2$ df -h
Filesystem                            Size  Used Avail Use% Mounted on
overlay                               120G  6.5G  113G   6% /
tmpfs                                  64M     0   64M   0% /dev
tmpfs                                 3.9G     0  3.9G   0% /sys/fs/cgroup
shm                                    64M     0   64M   0% /dev/shm
tmpfs                                 3.9G  3.4M  3.9G   1% /etc/passwd
/dev/xvdbv                            976M  2.6M  958M   1% /tmp/persistent
/dev/mapper/coreos-luks-root-nocrypt  120G  6.5G  113G   6% /etc/hosts
tmpfs                                 3.9G   24K  3.9G   1% /run/secrets/kubernetes.io/serviceaccount
tmpfs                                 3.9G     0  3.9G   0% /proc/acpi
tmpfs                                 3.9G     0  3.9G   0% /proc/scsi
tmpfs                                 3.9G     0  3.9G   0% /sys/firmware
bash-4.2$ cd /tmp/persistent
bash-4.2$ touch testfile
bash-4.2$ ls -lath
total 20K
drwxrwsr-x. 3 root       1000540000 4.0K Jan 31 17:28 .
-rw-r--r--. 1 1000540000 1000540000    0 Jan 31 17:28 testfile
drwxrwxrwt. 1 root       root         24 Jan 31 17:22 ..
drwxrws---. 2 root       1000540000  16K Jan 31 17:22 lost+found
bash-4.2$ exit
exit

  • Delete the deployment.

$ oc delete -f deploy-pvc.yml

  • Delete the persistent volume claim.

$ oc get pvc
NAME      STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
myclaim-userXX   Bound    pvc-a4a724b1-b711-40a1-a7c9-f89b7db209c7   1Gi        RWO            gp2            10m

$ oc delete pvc myclaim-userXX
persistentvolumeclaim "myclaim-userXX" deleted

  • Delete Project

$ oc delete project  pvc-demo-userXX

Summary

In this lab learned about persistent volumes and persistent volume claims. We then created a persistent volume claim and deployed an application.