研发工程师玩转Kubernetes——使用local型PV在不同Pod上共享数据
研发工程师玩转Kubernetes——使用local型PV在不同Pod上共享数据
PV清单
apiVersion: v1
kind: PersistentVolume
metadata:
name: default-storage-class-pv
spec:
capacity:
storage: 100Ki
volumeMode: Filesystem
accessModes:
- ReadWriteOnce
persistentVolumeReclaimPolicy: Retain
local:
path: /tmp/default_storage_class_pv
nodeAffinity:
required:
nodeSelectorTerms:
- matchExpressions:
- key: kubernetes.io/hostname
operator: In
values:
- ubuntud事先我们在Node ubuntud上创建一个空的目录/tmp/default_storage_class_pv。然后限定其大小是100K（后面测试发现不能控制住）。
PVC清单
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: default-storage-class-pvc
spec:
resources:
requests:
storage: 10Ki
volumeName: default-storage-class-pv
accessModes:
- ReadWriteOncePVC通过volumeName先PV default-storage-class-pv申请了10K空间（后面测试发现不能控制住）。
Pod使用VPC
# local_deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: local-pv-app-deployment
spec:
replicas: 2
selector:
matchLabels:
app: local-pv-app
template:
metadata:
labels:
app: local-pv-app
spec:
containers:
- name: local-pv-app
image: busybox
command: ["/bin/sh", "-c", "if [ -f /tempdir/lockfile ] && ! { set -C; 2>/dev/null >/tempdir/lockfile; }; then tail -f /tempdir/lockfile; else exec 3>/tempdir/lockfile; if [ -n \"$POD_NAME\" ]; then name=$POD_NAME; else name=\"unknown\"; fi; while true; do echo \"this is $name.$name write something to lockfile\"; echo \"$name write something to lockfile\" >&3; sleep 1; done; fi"]
volumeMounts:
- name: local-pvc-volume
mountPath: /tempdir
env:
- name: POD_NAME
valueFrom:
fieldRef:
fieldPath: metadata.name
volumes:
- name: local-pvc-volume
persistentVolumeClaim:
claimName: default-storage-class-pvc在spec.volumes.persistentVolumeClaim.claimName中，我们定义了之前申请的PVC名称。这样PVC就和这个Pod上的卷（local-pvc-volume）产生了关联。 在spec.containers[0].volumeMounts[0].name中，我们设置了Pod上卷的名称。mountPath表示挂载位置。即将该Pod上的卷（local-pvc-volume）挂载到/tempdir目录。
测试
依次创建完PV、PVC和Deployment后，我们观察不同Pod上表现。
kubectl exec pods/local-pv-app-deployment-56d955856f-llgvr -- tail -f /tempdir/lockfilelocal-pv-app-deployment-56d955856f-llgvr write something to lockfile local-pv-app-deployment-56d955856f-llgvr write something to lockfile local-pv-app-deployment-56d955856f-llgvr write something to lockfile ……
kubectl logs pods/local-pv-app-deployment-56d955856f-2hq28local-pv-app-deployment-56d955856f-llgvr write something to lockfile local-pv-app-deployment-56d955856f-llgvr write something to lockfile local-pv-app-deployment-56d955856f-llgvr write something to lockfile ……
可以发现Deployment创建的两个Pod共享了/tempdir/lockfile文件，且local-pv-app-deployment-56d955856f-llgvr负责写入，local-pv-app-deployment-56d955856f-2hq28负责读取。
storage有效性
理论上，如果/tempdir/lockfile文件大小达到PVC申请的10K或者PV规定的100K时，脚本继续写入将失败。但是我们通过频繁获取文件大小会发现，该文件大小会一直膨胀。
kubectl exec pods/local-pv-app-deployment-56d955856f-llgvr -- ls -lh /tempdir/lockfile-rw-r–r-- 1 root root 2.4K Aug 9 10:25 /tempdir/lockfile -rw-r–r-- 1 root root 9.8K Aug 9 10:26 /tempdir/lockfile -rw-r–r-- 1 root root 10.0K Aug 9 10:26 /tempdir/lockfile -rw-r–r-- 1 root root 10.1K Aug 9 10:26 /tempdir/lockfile -rw-r–r-- 1 root root 99.7K Aug 9 10:49 /tempdir/lockfile -rw-r–r-- 1 root root 100.0K Aug 9 10:49 /tempdir/lockfile -rw-r–r-- 1 root root 100.1K Aug 9 10:49 /tempdir/lockfile -rw-r–r-- 1 root root 593.4K Aug 9 12:51 /tempdir/lockfile