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

[TOC]

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: v1
kind: PersistentVolumeClaim
metadata:
name: pvc-test
spec:
accessModes:
- ReadWriteOnce
storageClassName: ceph-rbd
resources:
requests:
storage: 1Gi

nginx.yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: nginx-rbd
spec:
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]# ll
total 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   AGE
pvc-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-rbd
nginx-rbd
b60
-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.html
ygqygq2
[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   AGE
pvc-test   Bound    pvc-069c4486-d773-11e8-bd12-000c2931d938   1Gi        RWO            ceph-rbd       4m10s
[root@lab1 test]# kubectl delete pvc pvc-test  # 删除PVC
persistentvolumeclaim "pvc-test" deleted
[root@lab1 test]# kubectl get pv pvc-069c4486-d773-11e8-bd12-000c2931d938
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS     CLAIM              STORAGECLASS   REASON   AGE
pvc-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   AGE
pvc-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PV
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS     CLAIM              STORAGECLASS   REASON   AGE
pvc-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.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
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/pe
b68
rsistentvolumes/pvc-069c4486-d773-11e8-bd12-000c2931d938
uid: 06b57ef7-d773-11e8-bd12-000c2931d938
spec:
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-rbd
status:
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   AGE
pvc-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: v1
kind: PersistentVolumeClaim
metadata:
name: pvc-test-new
spec:
accessModes:
- ReadWriteOnce
storageClassName: ceph-rbd
resources:
requests:
storage: 1Gi

new_nginx.yaml

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: nginx-rbd
spec:
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   AGE
pvc-test           Bound    pvc-f2df48ea-d773-11e8-b6c8-000c29ea3e30   1Gi        RWO            ceph-rbd       31m
pvc-test-new       Bound    pvc-069c44
111c
86-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-rbd
nginx-rbd-79bb766b6c-mv2h8          1/1     Running   0          20m
[root@lab1 test]# kubectl exec -it nginx-rbd-79bb766b6c-mv2h8 -- ls /usr/share/nginx/html
lost+found  ygqygq2.html
[root@lab1 test]# kubectl exec -it nginx-rbd-79bb766b6c-mv2h8 -- cat /usr/share/nginx/html/ygqygq2.html
ygqygq2

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