前言

今天來講儲存篇，
為了撐滿30天，保險起見，儲存篇，依據內容順序分2天po
真怕PO錯篇@@~金恐布

Storage(Volumes)

Kubernetes Volume主要解決2個需求:

• 在container中的資料是短暫的，當container掛掉的時候，kubelet會重啟container，檔案就不見囉~
• 1個pod可以跑n個container，這些container通常需要共用檔案

參考:
https://kubernetes.io/docs/concepts/storage/
為了作Managing Storage，PersistentVolume提供2個API resources:PV、PVC

PersistentVolume (PV) 你家開一口「井」

另外寫一個volumes的yaml，用$ kubectl create -f volumes.yaml，
要簡化的話也可以跟deployment寫在一起

• 1、在cluster級中由administrator配置的storage
• 2、或者當pvc要求時動態配置(dynamically provisioned)，當pvc刪掉時也會自動消失

PV定義要mount外部的storage:(不只這些，詳細看官網喔)

• Local Disk
• Directory on the Host(只適合測試，不要用在production喔)
• Network Mount(公司內部的)
• Cloud Storage service(provider的)
• PersistentVolumeClaim (PVC) 從「井」弄「1盆水」來用

定義在deployment的yaml裡

層級較小POD，PVC 去用 PV 的資源，要求size、讀/寫模式(accessModes)、使用次數

PV、PVC都獨立於pod lifecycles之外

PersistenVolume

先定義PV

kind:PersistentVolume
apiVersion:v1
metadata:
	name:task-pv-volume
	labels:
		type:local

spec:
	storageClassName:manual
	capacity:
		sotrage:10Gi
	accessModes:
		-ReadWriteOnce
	hostPath:
		path:"/mnt/data"

• run一下寫好的yaml

$ kubectl create -f local-volumes.yaml

再定義PVC # 寫在deployment裡，例如:nginx-deployment.yaml

• 用Claim去PV找有無符合需求的:
  (a)有就分配:binds the claim to the volume
  (b)沒有就報錯:error

kind:PersistentVolumeClaim # 用Claim去PV找有無符合需求的，有就分配，沒有就報錯
apiVersion:v1
metadata:
	name:task-pv-claim # 跟pv要資源
spec:
	storageClassName:manual
	accessModes:
		-ReadWriteOnce
	resources:
		requests:
			storage:2Gi 

$ kubectl apply -f nginx-deployment.yaml
$ minikube service nginx --url # 看連結，用browser或curl跑看看

我們來找個範例，google關鍵字「kubernetes wordpress deployment」
因為wordpress會用到資料庫，這裡介紹的東西其實都寫在deployment
所以這樣一查，不只yaml檔，連指令都有
所以我找到了官網文件 = =…
https://kubernetes.io/docs/tutorials/stateful-application/mysql-wordpress-persistent-volume/
完整步驟請看文件喔，我只截要說明的

• application/wordpress/mysql-deployment.yaml

apiVersion: v1
kind: Service # 我要在pod跑1個container
metadata:
  name: wordpress-mysql
  labels:
    app: wordpress
spec:
  ports:
    - port: 3306
  selector:
    app: wordpress
    tier: mysql
  clusterIP: None
---
apiVersion: v1
kind: PersistentVolumeClaim # PVC
metadata:
  name: mysql-pv-claim
  labels:
    app: wordpress
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi
---
apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2
kind: Deployment
metadata:
  name: wordpress-mysql
  labels:
    app: wordpress
spec:
  selector: # 前面介紹過的selector，所以設定label很重要
    matchLabels:
      app: wordpress # 前端ap
      tier: mysql # 後端資料庫，放wordpress的資料
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: wordpress
        tier: mysql
    spec:
      containers:
      - image: mysql:5.6
        name: mysql
        env:
        - name: MYSQL_ROOT_PASSWORD
          valueFrom:
            secretKeyRef: # 寫在secrets裡面，以後在介紹
              name: mysql-pass
              key: password # 因為yaml檔可能會push到github，總不能把password放進去吧?
        ports:
        - containerPort: 3306
          name: mysql
        volumeMounts:
        - name: mysql-persistent-storage # 也是要取名字的
          mountPath: /var/lib/mysql # mysql預設放data的地方
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-pv-claim # claim也是要取名字的，以後可下$ kubectl get pvc

提早出現的secret，後面還會介紹

# 把MySQL的password放在secret
# secret 後面還會介紹
# secret object name: mysql-pass 
# key: password 
# 範例上面有喔
$ kubectl create secret generic mysql-pass --from-literal=password=YOUR_PASSWORD
$ kubectl get secrets

# deploy mysql
$ kubectl create -f https://k8s.io/examples/application/wordpress/mysql-deployment.yaml

# 各種delete
$ kubectl delete secret mysql-pass
$ kubectl delete deployment -l app=mysql
$ kubectl delete service -l app=mysql

# 連PersistentVolumeClaims(PVC)也能刪，動態配置的PersistentVolumes也會自動刪除。
$ kubectl delete pvc -l app=mysql

其他類型的 Volumes

範例請參考:
https://github.com/kubernetes/examples/tree/master/staging/volumes

emptyDir

掛一個空的目錄，同一個Pod中container都可以存取此目錄，Pod刪掉就沒了
常用來當暫存區，/tmp

apiVersion: v1
kind: Pod
metadata:
  name: test-pd
spec:
  containers:
  - image: k8s.gcr.io/test-webserver
    name: test-container
    volumeMounts:
    - mountPath: /cache # 掛到/cache
      name: cache-volume
  volumes:
  - name: cache-volume
    emptyDir: {} # 1、空目錄寫法

hostPath

• 掛host的目錄

apiVersion: v1
kind: Pod
metadata:
  name: test-pd
spec:
  containers:
  - image: k8s.gcr.io/test-webserver
    name: test-container
    volumeMounts:
    - mountPath: /test-pd
      name: test-volume
  volumes:
  - name: test-volume
    hostPath:
      # directory location on host
      path: /data
      # this field is optional
      type: Directory
# 其他的type
# DirectoryOrCreate:沒果沒這個目錄，會自動建一個空目錄，權限是0755
# FileOrCreate:如果沒有這個檔案，會建一個空檔案，權限0644 
# Socket:A UNIX socket

local

• 掛載local storage，例如:磁碟
  跟hostPath很像，但在其他文件有看到不太建議使用直接掛local storage

apiVersion: v1
kind: PersistentVolume
metadata:
  name: example-pv
  annotations:
        "volume.alpha.kubernetes.io/node-affinity": '{
            "requiredDuringSchedulingIgnoredDuringExecution": {
                "nodeSelectorTerms": [
                    { "matchExpressions": [
                        { "key": "kubernetes.io/hostname",
                          "operator": "In",
                          "values": ["example-node"]
                        }
                    ]}
                 ]}
              }'
spec:
    capacity:
      storage: 100Gi
    accessModes:
    - ReadWriteOnce
    persistentVolumeReclaimPolicy: Delete
    storageClassName: local-storage # <=== here
    local: # <=== here
      path: /mnt/disks/ssd1  # <=== here

iSCSI

要掛iSCSI，當然要有個iSCSI server
家裡有NAS的可以玩看看，
iSCSI initiator(windows內建，macOS還要另外買(globalSAN initiator)
有遇到這情境再參考範例:
https://github.com/kubernetes/examples/tree/master/staging/volumes/iscsi