Volume

K8S study notes

2020-01-25 09:11:51 936 words 5 minutes 次阅读量

Contents

1. emptyDir

It’s the basis of Volume. The life cycle depends on the Pod. The volume will be removed when the related Pod was removed. So we can think of it as the path of the Pod. All the containers of the pod share this voiume. Let’s show how to setup the volume configure.

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apiVersion: v1
kind: Pod
metadata:
 name: producer-consumer
spec:
 containers:
 - image: busybox
   name: producer
   volumeMounts:
   - mountPath: /producer_dir
     name: shared-volume
   args:
   - /bin/sh
   - -c
   - echo "hello world" > /producer_dir/hello; sleep 30000

 - image: busybox
   name: consumer
   volumeMounts:
   - mountPath: /consumer_dir
     name: shared-volume
   args:
   - /bin/sh
   - -c
   - cat /consumer_dir/hello; sleep 30000

 volumes:
 - name: shared-volume
   emptyDir: {}

The above file is about configure the volume practice. We design two containers in the pod, one is to producer, write the log in the path file, another is to consumer, read the log from the file. It’s easy to understand that these two containers share the storage from the pod.

2. HostPath

It’s rare to use this kind of volume. It’s not common. This for Docker host mount the existing path to the Pod. So Pod and containers have very strong coupling. But if pod was removed, the volume is still existing. However, avoid using this kind of volume.

3. Extern Storage Provider

This used extern storage provider to achieve the volume. For example, use the AWS，GCE or Azure and so on. Let me show the configure.

This used the aws storage. The strength about using this is to make the k8s cluster and volume isolated. There is no impact when the k8s cluster destroyed.

4. PersistentVolume & PersistentVolumeClaim

From section 3, we know we can use the extern storage for the k8s volume. But there is one question, actually the storage system always for administration, but the k8s deployment is for developer. There are different departments. How to balance the gap. The solving method is PV and PVC.

PV is maintained by the administration, it’s the extern storage arranged. But PVC is for developer. When deploy the micro service, they can set up the pvc to arrange the space from PV. So PV and PVC coordinate to deploy the whole system.

4.1 NFS PersistentVolume

At first, install the NFS service in the master and slave nodes. Also define the mount path. Below are the PV and PVC configure file.

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nfs-pv.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
 name: mypv1
spec:
 capacity:
   storage: 1Gi
 accessModes:
   - ReadWriteOnce
 persistentVolumeReclaimPolicy: Recycle
 storageClassName: nfs
 nfs:
   path: /tmp/pv1
   server: 10.128.0.2

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nfs-pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
 name: mypvc1
spec:
 accessModes:
   - ReadWriteOnce
 resources:
   requests:
     storage: 1Gi
 storageClassName: nfs

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pod.yaml
apiVersion: v1
kind: Pod
metadata:
 name: mypod1
spec:
 containers:
   - name: mypod1
     image: busybox
     args:
     - /bin/sh
     - -c
     - sleep 30000
     volumeMounts:
     - mountPath: "/mydata"
       name: mydata
 volumes:
   - name: mydata
     persistentVolumeClaim:
       claimName: mypvc1

In the PV YAML file, we can define the persistent volume policy type. There are 3 types: Retain,Recycle,and Delete.The default policy is Delete.

Retain: Users deletes a persistentVolumeClaim.the corresponding persistentVolume is not deleted. Instead, it’s moved to the release phase, where all of its data can be manually recovered.
Recycle: It’s different with Retain, the data can’t be manually recovered when delete the PVC.
Delete: It’s default mode. Means a dynamically pv is automatically deleted when a user deleted the corresponding pic.

When run the pod, will mount the PVC path. Then use command to write something to the mount path. From the below running result, we can understand the PV and PVC in the NFS.

About is the static provision, there is another kind of provision, it’s the dynamical provision. It arranges the storage according to the situation.

4.2 Database Practice

Background: use NFS PV and PVC to database backup when the node shutdown to verify the data persistence.

Steps:

Deploy the PV and PVC according to the below configure files.

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mysql-pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
 name: mysql-pvc
spec:
 accessModes:
   - ReadWriteOnce
 resources:
   requests:
     storage: 1Gi
 storageClassName: nfs

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mysql-pv.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
 name: mysql-pv
spec:
 accessModes:
   - ReadWriteOnce
 capacity:
   storage: 1Gi
 persistentVolumeReclaimPolicy: Retain
 storageClassName: nfs
 nfs:
   path: /tmp/mysql-pv
   server: 10.128.0.2	

Deploy the mysql pod and service.

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piVersion: v1
kind: Service
metadata:
 name: mysql
spec:
 ports:
 - port: 3306
 selector:
   app: mysql

---
apiVersion: apps/v1
kind: Deployment
metadata:
 name: mysql
spec:
 selector:
   matchLabels:
     app: mysql
 template:
   metadata:
     labels:
       app: mysql
   spec:
     containers:
     - image: mysql:5.6
       name: mysql
       env:
       - name: MYSQL_ROOT_PASSWORD
         value: password
       ports:
       - containerPort: 3306
         name: mysql
       volumeMounts:
       - name: mysql-persistent-storage
         mountPath: /var/lib/mysql
     volumes:
     - name: mysql-persistent-storage
       persistentVolumeClaim:
         claimName: mysql-pvc

Use the client to access the database, insert some messages into the database.
Shutdown the node1, then the database will be automatically backup to the node2. After backup, we can verify in the master node.