k8s Storage Data Persistence, emptyDir, hostPath, Nfs-based PV, PVC

Containers exist in both docker and K8S and have a life cycle, so data volumes can be used for data persistence.

Key issues addressed by data volumes:

1. Data persistence: When we write data, the files are temporary. When the container crashes, the host kills the container, then re-creates the container from the mirror, and the data is lost.

2. Data sharing: Running containers in the same Pod requires sharing files.

Type of data volume:

The emptyDir data volume is similar to the docker manager volume for docker data persistence. When initially assigned, the data volume is an empty directory in which a container in the same Pod can perform read and write operations and share data.
Scene features: one same pod, different containers, shared data volumes
If the container is deleted, the data still exists, and if the Pod is deleted, the data is deleted


**vim  emptyDir.yaml**
apiVersion: v1
kind: Pod
  name: producer-consumer
  - image: busybox
    name: producer
    - mountPath: /producer_dir#Here the path refers to the path within the container
      name: shared-volume#Specify a local directory name
    args:#Define what happens when the container runs
    - /bin/sh
    - -c
    - echo "hello k8s" > /producer_dir/hello; sleep 30000

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

  - name: shared-volume#The value here needs to correspond to the name value of the mountPath of the Pod above
    emptyDir: {}#Define the type of data persistence that represents an empty directory

Kubectl apply-f emptyDir.yaml #execute file
Docker inspect (see container details): Mount mount point

You can enter the directory to view the data on the host machine.

Kubectl get pod-o wide (-w): can view pod information in detail
Add-w: you can view it in real time.And know which node the container is running on.

kubectl logs {pod name} consumer can view the data in the directory.

Depending on the test, you can see the containers on the nodes and whether the mount directories are the same.The same is true.You can delete the container to see if the data is lost, and delete the master node pod to see if the data is still there.
According to tests, emptyDir data persistence is generally only used as temporary storage.

2.hostPath Volume
1) Mount a file or directory on the file system of the Pod node into a container.
2) A bind mount similar to docker data persistence.If the Pod is deleted, the data remains.It's better than emptyDir, but once the host crashes, hostPath can't be accessed.
3) There are few scenarios where this data persistence is used because it increases the coupling between Pod and nodes.

3. Persistent Volume: The directory where the pv (persistent volume) stores data persistence, done in advance.
    persistentVolumeClaim: PVC (Persistent Volume Use Statement|Request)
    The pvc is a user-stored request.Similar to pod.Pod consumes node resources, pvc consumes storage resources.A pod can request a specific level of resources (cpu, memory).The pvc can request specific sizes and access modes based on permissions.

PV based on NFS services:

install NFS Services and rpcbind Services:
1.[root@master yaml]# yum install -y nfs-utils rpcbind  #Note here that all three install NFS services.
2.[root@master yaml]# vim /etc/exports  
//Add / nfsdata * (rw,sync,no_root_squash) to the file
4.[root@master yaml]# mkdir /nfsdata  
5.[root@master yaml]# systemctl start rpcbind  
6.[root@master yaml]# systemctl start nfs-server.service   
7.[root@master yaml]# showmount -e  
Export list for master:  
/nfsdata *  

Create a PV resource object:

vim nfs-pv.yaml
apiVersion: v1
kind: PersistentVolume
  name: test
  capacity:#Capacity given
    storage: 1Gi
  accessModes:#PV Supported Access Mode
    - ReadWriteOnce#This means that you can only mount to a single node read-write
  persistentVolumeReclaimPolicy: Recycle#Recycle policy for pv: Indicates clear data automatically
  storageClassName: nfs#Defined Storage Class Name
  nfs:#This should match the storage class name defined above
    path: /nfsdata/pv1#Specify a directory for NFS
    server: the IP of the NFS server
implement nfs-pv.yaml Files:
**` kubectl apply -f nfs-pv.yaml  ` **
persistentvolume/test created  
**` kubectl get pv  `**
test   1Gi        RWO            Recycle         ** Available **          nfs                     7s  
**Note here STATUS Status is Available To be able to use.**

Access modes supported by pv:
ReadWriteOnce: Access mode is to mount to a single node read-write only
ReadWriteMany: Access mode is to mount to multiple nodes read-write only
ReadOnlyMany: Access mode is to mount to multiple nodes in a read-only manner only
Recycling strategies for PV storage:
Recycle: Automatically clean up data.
Retain: Manual recycling by an administrator is required.
Delete: Cloud storage dedicated.
PV and PVC are related to each other: through storageClassName and accessModes

Establish PVC: 
 vim nfs-pvc.yaml
apiVersion: v1
kind: PersistentVolumeClaim
  name: test
    - ReadWriteOnce#Define the access mode, which must be consistent with the Pv definition
      storage: 1Gi#Size of Request Capacity
  storageClassName: nfs#The name of the storage class must match the pv definition.

Run and view PVC and PV:
kubectl apply -f nfs-pvc.yaml   
As you will see when you associate, Bound:

Keywords: Docker vim yum

Added by joe1986 on Sat, 15 Feb 2020 07:51:36 +0200