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云原生 | K8s中VolumeMounts.subPath的巧妙用法

 1 year ago
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有时，在单个 Pod 中共享卷以供多方使用是很有用的。volumeMounts.subPath 属性可用于指定所引用的卷内的子路径，而不是其根路径。

官方文档：https://kubernetes.io/zh-cn/docs/concepts/storage/volumes/#using-subpath

二、使用场景

  1. 一个共享卷, 挂载多个路径。
  2. ConfigMap或Secret挂载到特定目录的特定路径, 而 该目录下已经有其他文件且不希望被覆盖掉。

三、共享卷中使用, 挂载多个路径

作为configmap/secret使用时,subPath代表configmap/secret的子路径。

【示例1】挂载目录，hostPath

apiVersion: v1
kind: Pod
metadata:
  name: my-lamp-site
spec:
    nodeName: local-168-182-110 # 为了测试方便，指定调度机器
    containers:
    - name: mysql
      image: mysql
      env:
      - name: MYSQL_ROOT_PASSWORD
        value: "rootpasswd"
      volumeMounts:
      - mountPath: /var/lib/mysql #挂载到容器的某个路径下
        name: site-data #挂载设备的名字，与volumes[*].name 需要对应 
        subPath: mysql # volumes path中的子路径（会自动在volumes path目录下创建mysql空目录）
    - name: php
      image: php:7.0-apache
      volumeMounts:
      - mountPath: /var/www/html #挂载到容器的某个路径下
        name: site-data # volumes path中的子路径（会自动在volumes path目录下创建site-data【空目录】）
        subPath: html
    volumes:
      - name: nginx #和上面保持一致 这是本地的文件路径，上面是容器内部的路径
        hostPath:
          path: /opt/k8s/subPath/lamp #此路径需要实现创建

【示例2】挂载目录，pvc

# StorageClass
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer
---
# pvc 
apiVersion: v1
kind: PersistentVolume
metadata:
  name: local-lamp-pv
  labels:
    name: local-lamp-pv
spec:
  capacity:
    storage: 1Gi
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: local-storage
  local:
    path: /opt/k8s/subPath/lamp-pvc
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - local-168-182-110

---
# pvc 
kind: PersistentVolumeClaim
apiVersion: v1
metadata:
  name: my-lamp-site-data
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 1Gi 
  storageClassName: local-storage
  selector:
    matchLabels:
      name: local-lamp-pv
---
apiVersion: v1
kind: Pod
metadata:
  name: my-lamp-site-pvc
spec:
    containers:
    - name: mysql
      image: mysql
      env:
      - name: MYSQL_ROOT_PASSWORD
        value: "rootpasswd"
      volumeMounts:
      - mountPath: /var/lib/mysql
        name: site-data
        subPath: mysql
    - name: php
      image: php:7.0-apache
      volumeMounts:
      - mountPath: /var/www/html
        name: site-data
        subPath: html
    volumes:
    - name: site-data
      persistentVolumeClaim:
        claimName: my-lamp-site-data

如果使用PVC模板就不用手动创建PVC了，示例如下：

  volumeClaimTemplates:   #可看作pvc的模板
  - metadata:
      name: nginx-pvc
    spec:
      accessModes: [ "ReadWriteOnce" ]
      storageClassName: "local-storage"  #存储类名，就是上面nginx-sc.yaml metadata.name
      resources:
        requests:
          storage: 1Gi

【示例3】共享单个文件那么如果 subPath 不是文件夹，而是一个文件，又该如何解决呢？同样的道理，只需要通过 subPath 指定出该文件即可，注意 subPath 要使用相对目录。具体如下所示：

apiVersion: apps/v1
kind: Deployment
metadata:
  name: deployment-test
spec:
  replicas: 1
  selector:
    matchLabels:
     app: nginx-pod
  template:
    metadata:
      labels:
        app: nginx-pod
    spec:
      nodeName: local-168-182-110 # 为了测试方便，指定调度机器
      containers:
      - name: nginx
        image: docker.io/library/nginx:latest
        volumeMounts:
        - mountPath: /etc/nginx/nginx.conf
          name: nginx-conf
          subPath: nginx-conf
      volumes:
      - name: nginx-conf #和上面保持一致 这是本地的文件路径，上面是容器内部的路径
        hostPath:
          path: /opt/k8s/subPath/nginx #此路径需要实现创建
图片

【结论】以宿主机上的文件为准，会覆盖pod里原先默认的的文件内容。

四、ConfigMap 和 Secret 中使用 subPath

作为configmap/secret使用时,subPath代表configmap/secret​的子路径。如果不使用subPath​会把容器里原本的文件（volumeMounts.mountPath​对应的目录）都清空，自会把ConfigMap 和 Secret 的文件放在volumeMounts.mountPath对应的目录下。

【示例1】ConfigMap

apiVersion: v1
kind: ConfigMap
metadata: 
  name: nginx-conf
data:
  nginx.conf: |+
    worker_processes  1;
    events {
        worker_connections  1024;
    }
    http {
        include       mime.types;
        default_type  application/octet-stream;
        sendfile        on;
        keepalive_timeout  65;
        server {
            listen       80;
            server_name  localhost;
            location / {
                root   html;
                index  index.html index.htm;
            }
            error_page   500 502 503 504  /50x.html;
            location = /50x.html {
                root   html;
            }
        }
    }
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: deployment-test2
spec:
  replicas: 1
  selector:
    matchLabels:
     app: nginx-pod
  template:
    metadata:
      labels:
        app: nginx-pod
    spec:
      nodeName: local-168-182-110 # 为了测试方便，指定调度机器
      containers:
      - name: nginx
        image: docker.io/library/nginx:latest
        volumeMounts:
        - name: nginx-cm # 与volumes.name一致
          mountPath: /etc/nginx/nginx.conf
          subPath: nginx.conf
      volumes:
      - name: nginx-cm
        configMap:
          name: nginx-conf # configMap名称

【示例1】Secret

apiVersion: v1
kind: Secret
metadata:
  name: mysecret
type: Opaque
data:
  username: admin
  password: MWYyZDFlMmU2N2Rm

---

vim myapp-demo.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: mysql-demo
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: myapp
        image: mysql
        imagePullPolicy: IfNotPresent
        ports:
        - name: http
          containerPort: 80
        volumeMounts:
        - name: mysql
          mountPath: /tmp/data
          subPath: data
      volumes:
      - name: mysql
        secret:
          secretName: mysecret

【结论】会在/tmp目录下面存放data文件信息，如果存在则覆盖。如果不存在，则自动创建。

最后对volumeMounts.subPath来一个总结：

  • subPath其实就是volumes挂载的子目录或单个文件，是不是目录和单文件，取决于subPath在volumes挂载的目录下是否存在subPath定义的文件（文件或目录），如果不存在，则会volumes对应的目录下创建一个subPath目录。
  • 如果ConfigMap 和 Secret 中使用 subPath，如果不指定subPath，则会把volumeMounts.mountPath对应的目录下的文件都清掉，然后只存放ConfigMap 或者 Secret 定义的文件。

关于volumeMounts.subPath的用法就先到这里了，有疑问的小伙伴，欢迎给我留言哦，后续文章更精彩，请小伙伴耐心等待哦~


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