[Cloud] 11. Using Kubernetes Volume

Volume Overview

In this post, we will learn about the concept of Volume and how to use it in Kubernetes.

The schematic structure of Volume on Kubernetes is as shown in the figure above. Using the Volume parameter of Pod, define the value of PVC (persistent volume claim), and use this value to send the PVC to the PV (Persistent Volume) mapped to the storage to send the Pod This is the structure that maps the PV to be used in

Volume Type

Then let's learn about Volume Type. There are 4 types and 2 types of Volume as follows.

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kind of Volume Type

• emptyDirtmp is a Volume that exists in the Pod when the Pod is created. That is, when the Pod is deleted, all data is also deleted.
• hostPath(Local) is used by mounting the file or directory of the host node to the Pod, and its contents are not deleted when the Pod is deleted.
• local uses a file system mounted on a specific lost node as a Volume.
• Network : Use storage that exists on the network or cloud as a Volume. (AWS, NFS, EBS, etc.)

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Classification according to Volume Provisioning Type (Volume is automatically created or not)

• Static Volume Provisioning: Administrators manually create Persistent Volumes in Kubernetes
• DynamicVolume Provisoning automatically creates a persistent volume in Kubernetes at the request of the developer.

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Persistent Volume(PV) & Persistent Volume Claim(PVC)

Using volumes in Kubernetes consists of two steps, as mentioned above. priority PersistentVolume (PV) to which storage is mapped, and PersistentVolumeClaim (PVC), which requests volume details with PV when using that PV in Pods, are separated into two stages. You can think of PV as storage itself. PVC means a request from a developer or cloud user to allocate a Volume to a PV. Set the capacity you want to use and the setting values ​​for various volumes and make a request.

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So let's take a look at the PV yaml file.

apiVersion: v1 kind: PersistentVolume ==> define Object Type metadata: name: pv0003 ==> name of PV spec: ==> define PV Spec capacity: storage: 5Gi ==> capacity Volume volumeMode: Filesystem ==> define type of Volume accessModes: ==> define Access Mode - ReadWriteOnce persistentVolumeReclaimPolicy: Recycle storageClassName: slow mountOptions: ==> Volume mount info - hard - nfsvers=4.1 nfs: path: /tmp server: 172.17.0.2

If you look at the yaml file above, PV is being created, the capacity is 5G, and the NFS type volume is defined. Like Pods, Volumes have the following states.

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Phase

• Available: The state in which the PV is created and before the PVC is bound.
• Bound – PVC bound to PV
• Released – the PVC has been deleted
• Failed – Failed status

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If you look at the above parameter, there is AccessMode. This is the part that sets what kind of access to the Volume is allowed. A look at each mode is as follows.

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Access Modes

• ReadWriteOnce – A volume can be mounted read-write by a single node.
• ReadOnlyMany – Volumes can be mounted read-only by multiple nodes.
• ReadWriteMany – Volumes can be mounted read-write by multiple nodes.

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In the above Yaml file, there is a Reclaim Policy parameter. This parameter is the part that defines how to handle the file on the disk connected to the PV when the PVC bound to a specific PV is deleted. So let's see what values ​​do what.

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Reclaim Policy

• Retain – Retain PV and data even if PVC is deleted (requires deletion and re-creation of PV to re-write)
• Recycle – Keep PV but delete file (rm -rf /thevolume/*)
• Delete – Delete volume and data

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Now let's look at the PVC sample yaml file.

root@master-VirtualBox:~/test/persistenvolume# vi pvc.yaml apiVersion: v1 kind: PersistentVolumeClaim ==> define type of Object metadata: name: myclaim ==> name of PVC spec: accessModes: - ReadWriteOnce volumeMode: Filesystem resources: requests: storage: 8Gi ==> requested quota storageClassName: slow ==> defind IO(Input/Output) Speed selector: matchLabels: release: "stable" matchExpressions: - {key: environment, operator: In, values: [dev]}

excerise

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Now, let's use Volume. First, create a password for mysql as a secret object.

root@master-VirtualBox:~# kubectl create secret generic mysql-pass --from-literal=password=pwd secret/mysql-pass created

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Now, create a yaml file like the one below and save it after entering the following contents

root@master-VirtualBox:~/test# mkdir persistenvolume root@master-VirtualBox:~/test# cd persistenvolume/ root@master-VirtualBox:~/test/persistenvolume# vi pv-yaml apiVersion: v1 kind: PersistentVolume metadata: name: wp-pv-volume labels: type: local spec: capacity: storage: 3Gi volumeMode: Filesystem accessModes: - ReadWriteMany persistentVolumeReclaimPolicy: Delete storageClassName: local-storage local: path: "/data/mysql" nodeAffinity: required: nodeSelectorTerms: - matchExpressions: - key: kubernetes.io/hostname operator: In values: - node

Then, create a PVC yaml file, input the file contents and save it.

root@master-VirtualBox:~/test/persistenvolume# vi pvc.yaml kind: PersistentVolumeClaim apiVersion: v1 metadata: name: mysql-pv-claim spec: storageClassName: local-storage accessModes: - ReadWriteMany resources: requests: storage: 2Gi selector: matchLabels: type: local

Now, create a mysql Pod yaml file as a Backend (DB) Pod, enter the following content and save it.

root@master-VirtualBox:~/test/persistenvolume# vi mysql-deployment.yaml apiVersion: apps/v1 kind: Deployment metadata: name: wordpress-mysql labels: app: wordpress spec: selector: matchLabels: app: wordpress tier: mysql strategy: type: Recreate template: metadata: labels: app: wordpress tier: mysql spec: containers: - image: mysql:5.6 imagePullPolicy: Always name: mysql env: - name: MYSQL_ROOT_PASSWORD valueFrom: secretKeyRef: name: mysql-pass key: password ports: - containerPort: 3306 name: mysql volumeMounts: - name: mysql-persistent-storage mountPath: /var/lib/mysql volumes: - name: mysql-persistent-storage persistentVolumeClaim: claimName: mysql-pv-claim ==> 위에서 생성한 PVC의 이름

Now, create a yaml file to create a Service object for communication between Pods, enter the following content and save it.

root@master-VirtualBox:~/test/persistenvolume# vi mysql-svc.yaml apiVersion: v1 kind: Service metadata: name: wordpress-mysql labels: app: wordpress spec: ports: - port: 3306 selector: app: wordpress tier: mysql clusterIP: None

Now, create a yaml file to create a Pod that provides Wordpress service with Frontend, enter the following content and save it

root@master-VirtualBox:~/test/persistenvolume# vi wp-deployment.yaml apiVersion: apps/v1 kind: Deployment metadata: name: wordpress labels: app: wordpress spec: selector: matchLabels: app: wordpress tier: frontend strategy: type: Recreate replicas: 1 template: metadata: labels: app: wordpress tier: frontend spec: containers: - image: wordpress:4.8-apache imagePullPolicy: Always name: wordpress env: - name: WORDPRESS_DB_HOST value: wordpress-mysql - name: WORDPRESS_DB_PASSWORD valueFrom: secretKeyRef: name: mysql-pass key: password ports: - containerPort: 80 name: wordpress

Then, to create a Service Object for communication with the Frontend Pod, create a Service yaml file, enter the following, and save it.

oot@master-VirtualBox:~/test/persistenvolume# vi wp-svc.yaml apiVersion: v1 kind: Service metadata: name: wordpress labels: app: wordpress spec: type: NodePort ports: - port: 8080 targetPort: 80 protocol: TCP selector: app: wordpress tier: frontend

Now, after distributing all the created objects, search the information of the created object.

root@master-VirtualBox:~/test# kubectl apply -f /root/test/persistenvolume/ deployment.apps/wordpress-mysql created service/wordpress-mysql created persistentvolumeclaim/mysql-pv-claim created deployment.apps/wordpress created service/wordpress created ​ root@master:/lab/dashboard# kubectl get svc NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE kubernetes ClusterIP 172.168.1.1 <none> 443/TCP 4h56m wordpress NodePort 172.168.1.177 <none> 8080:32382/TCP 10m wordpress-mysql ClusterIP None <none> 3306/TCP 10m

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Now, send a service request to http://172.168.1.177:32382 to the part marked in red above, and check whether the volume is mounted under the data directory in the Worker Node where the Pod is running after checking whether it is received normally.

root@node:/data/mysql# ll total 110616 drwxr-xr-x 5 vboxadd vboxsf 4096 12월 5 15:39 ./ drwxr-xr-x 3 root root 4096 12월 5 15:12 ../ -rw-rw---- 1 vboxadd vboxsf 56 12월 5 15:38 auto.cnf -rw-rw---- 1 vboxadd vboxsf 12582912 12월 5 15:38 ibdata1 -rw-rw---- 1 vboxadd vboxsf 50331648 12월 5 15:38 ib_logfile0 -rw-rw---- 1 vboxadd vboxsf 50331648 12월 5 15:38 ib_logfile1 drwx------ 2 vboxadd vboxsf 4096 12월 5 15:38 mysql/ drwx------ 2 vboxadd vboxsf 4096 12월 5 15:38 performance_schema/ drwx------ 2 vboxadd vboxsf 4096 12월 5 15:39 wordpress/