Kubernetes PV在Retain策略Released状态下重新分配到PVC恢复数据

Kubernetes PV在Retain策略Released状态下重新分配到PVC恢复数据

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1. 实验目的和环境说明

原由：在使用helm update stable/sonatype-nexus从1.6版本更新到1.13版本后，出现PVC删除，重新创建PVC的情况，好在原来PV为Retain。故研究下Retain的PV怎么恢复数据。

实验目的：PVC删除后，PV因Retain策略，状态为Released，将PV内数据恢复成PVC，挂载到POD内，达到数据恢复。

环境说明：

• Kubernetes: 1.12.1
• StorageClass: ceph-rbd
• OS: CentOS7

2. 实验过程

准备yaml文件：

pvc.yaml

apiVersion: v1kind: PersistentVolumeClaimmetadata:  name: pvc-testspec:  accessModes:    - ReadWriteOnce  storageClassName: ceph-rbd   resources:    requests:      storage: 1Gi

nginx.yaml

apiVersion: extensions/v1beta1kind: Deploymentmetadata:  name: nginx-rbdspec:  replicas: 1  template:    metadata:      labels:        name: nginx    spec:      containers:        - name: nginx          image: nginx          imagePullPolicy: IfNotPresent          ports:            - containerPort: 80          volumeMounts:            - name: ceph-rbd-volume              mountPath: "/usr/share/nginx/html"      volumes:      - name: ceph-rbd-volume        persistentVolumeClaim:          claimName: pvc-test

新建pvc、deployment、写入数据并删除pvc操作过程：

[root@lab1 test]# lltotal 8-rw-r--r-- 1 root root 533 Oct 24 17:54 nginx.yaml-rw-r--r-- 1 root root 187 Oct 24 17:55 pvc.yaml[root@lab1 test]# kubectl apply -f pvc.yaml persistentvolumeclaim/pvc-test created[root@lab1 test]# kubectl get pvc NAME               STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGEpvc-test           Bound    pvc-069c4486-d773-11e8-bd12-000c2931d938   1Gi        RWO            ceph-rbd       7s[root@lab1 test]# kubectl apply -f nginx.yaml deployment.extensions/nginx-rbd created[root@lab1 test]# kubectl get pod |grep nginx-rbdnginx-rbd-7c6449886-thv25           1/1     Running   0          33s[root@lab1 test]# kubectl exec -it nginx-rbd-7c6449886-thv25 -- /bin/bash -c 'echo ygqygq2 > /usr/share/nginx/html/ygqygq2.html'        [root@lab1 test]# kubectl exec -it nginx-rbd-7c6449886-thv25 -- cat /usr/share/nginx/html/ygqygq2.htmlygqygq2[root@lab1 test]# kubectl delete -f nginx.yaml deployment.extensions "nginx-rbd" deleted[root@lab1 test]# kubectl get pvc pvc-test     NAME       STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGEpvc-test   Bound    pvc-069c4486-d773-11e8-bd12-000c2931d938   1Gi        RWO            ceph-rbd       4m10s[root@lab1 test]# kubectl delete pvc pvc-test  # 删除PVCpersistentvolumeclaim "pvc-test" deleted[root@lab1 test]# kubectl get pv pvc-069c4486-d773-11e8-bd12-000c2931d938NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS     CLAIM              STORAGECLASS   REASON   AGEpvc-069c4486-d773-11e8-bd12-000c2931d938   1Gi        RWO            Retain           Released   default/pvc-test   ceph-rbd                4m33s[root@lab1 test]# kubectl get pv pvc-069c4486-d773-11e8-bd12-000c2931d938 -o yaml > /tmp/pvc-069c4486-d773-11e8-bd12-000c2931d938.yaml  # 保留备用

从上面可以看到，pvc删除后，pv变成Released状态。

再次创建同名PVC，查看是否分配原来PV操作过程：

[root@lab1 test]# kubectl apply -f pvc.yaml persistentvolumeclaim/pvc-test created[root@lab1 test]# kubectl get pvc  # 查看新建的PVC              NAME               STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGEpvc-test           Bound    pvc-f2df48ea-d773-11e8-b6c8-000c29ea3e30   1Gi        RWO            ceph-rbd       19s[root@lab1 test]# kubectl get pv pvc-069c4486-d773-11e8-bd12-000c2931d938  # 查看原来的PVNAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS     CLAIM              STORAGECLASS   REASON   AGEpvc-069c4486-d773-11e8-bd12-000c2931d938   1Gi        RWO            Retain           Released   default/pvc-test   ceph-rbd                7m18s[root@lab1 test]# 

从上面可以看到，PVC分配的是新的PV，因为PV状态不是Available。

那怎么才能让PV状态变成Available呢？我们来查看之前的PV：

[root@lab1 test]# cat /tmp/pvc-069c4486-d773-11e8-bd12-000c2931d938.yamlapiVersion: v1kind: PersistentVolumemetadata:  annotations:    pv.kubernetes.io/provisioned-by: ceph.com/rbd    rbdProvisionerIdentity: ceph.com/rbd  creationTimestamp: 2018-10-24T09:56:06Z  finalizers:  - kubernetes.io/pv-protection  name: pvc-069c4486-d773-11e8-bd12-000c2931d938  resourceVersion: "11752758"  selfLink: /api/v1/persistentvolumes/pvc-069c4486-d773-11e8-bd12-000c2931d938  uid: 06b57ef7-d773-11e8-bd12-000c2931d938spec:  accessModes:  - ReadWriteOnce  capacity:    storage: 1Gi  claimRef:    apiVersion: v1    kind: PersistentVolumeClaim    name: pvc-test    namespace: default    resourceVersion: "11751559"    uid: 069c4486-d773-11e8-bd12-000c2931d938  persistentVolumeReclaimPolicy: Retain  rbd:    fsType: ext4    image: kubernetes-dynamic-pvc-06a25bd3-d773-11e8-8c3e-0a580af400d5    keyring: /etc/ceph/keyring    monitors:    - 192.168.105.92:6789    - 192.168.105.93:6789    - 192.168.105.94:6789    pool: kube    secretRef:      name: ceph-secret      namespace: kube-system    user: kube  storageClassName: ceph-rbdstatus:  phase: Released

从上面可以看到，spec.claimRef这段，仍保留之前的PVC信息。

我们大胆删除spec.claimRef这段。再次查看PV：

kubectl edit pv pvc-069c4486-d773-11e8-bd12-000c2931d938

[root@lab1 test]# kubectl get pv pvc-069c4486-d773-11e8-bd12-000c2931d938 NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS      CLAIM   STORAGECLASS   REASON   AGEpvc-069c4486-d773-11e8-bd12-000c2931d938   1Gi        RWO            Retain           Available           ceph-rbd                10m

从上面可以看到，之前的PV pvc-069c4486-d773-11e8-bd12-000c2931d938已经变为Available。

再次创建PVC、deployment，并查看数据：

new_pvc.yaml

apiVersion: v1kind: PersistentVolumeClaimmetadata:  name: pvc-test-newspec:  accessModes:    - ReadWriteOnce  storageClassName: ceph-rbd   resources:    requests:      storage: 1Gi

new_nginx.yaml

apiVersion: extensions/v1beta1kind: Deploymentmetadata:  name: nginx-rbdspec:  replicas: 1  template:    metadata:      labels:        name: nginx    spec:      containers:        - name: nginx          image: nginx          imagePullPolicy: IfNotPresent          ports:            - containerPort: 80          volumeMounts:            - name: ceph-rbd-volume              mountPath: "/usr/share/nginx/html"      volumes:      - name: ceph-rbd-volume        persistentVolumeClaim:          claimName: pvc-test-new

操作过程：

[root@lab1 test]# kubectl apply -f new_pvc.yaml persistentvolumeclaim/pvc-test-new created[root@lab1 test]# kubectl get pvc NAME               STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGEpvc-test           Bound    pvc-f2df48ea-d773-11e8-b6c8-000c29ea3e30   1Gi        RWO            ceph-rbd       31mpvc-test-new       Bound    pvc-069c4486-d773-11e8-bd12-000c2931d938   1Gi        RWO            ceph-rbd       27m[root@lab1 test]# kubectl apply -f new_nginx.yaml [root@lab1 test]# kubectl get pod|grep nginx-rbdnginx-rbd-79bb766b6c-mv2h8          1/1     Running   0          20m[root@lab1 test]# kubectl exec -it nginx-rbd-79bb766b6c-mv2h8 -- ls /usr/share/nginx/htmllost+found  ygqygq2.html[root@lab1 test]# kubectl exec -it nginx-rbd-79bb766b6c-mv2h8 -- cat /usr/share/nginx/html/ygqygq2.htmlygqygq2

从上面可以看到，新的PVC分配到的是原来的PV pvc-069c4486-d773-11e8-bd12-000c2931d938，并且数据完全还在。

3. 小结

当前版本Kubernetes PVC存储大小是唯一能被设置或请求的资源，因我们没有修改PVC的大小，在PV的Available状态下，有PVC请求分配相同大小时，PV会被分配出去并绑定成功。
在PV变成Available过程中，最关键的是PV的spec.claimRef字段，该字段记录着原来PVC的绑定信息，删除绑定信息，即可重新释放PV从而达到Available。

参考资料：
[1] https://kubernetes.io/docs/concepts/storage/persistent-volumes/
[2] https://kubernetes.io/docs/concepts/storage/storage-classes/
[3] http://dockone.io/article/2082
[4] http://dockone.io/article/2087