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K8S中的mountPath和subPath使用詳解

更新時(shí)間：2024年12月20日 08:31:38 作者：Blue?summer

這篇文章主要介紹了K8S中的mountPath和subPath使用的相關(guān)資料,通過示例展示了如何使用mountPath和subPath來掛載ConfigMap到Pod中,并解決了服務(wù)無法啟動(dòng)的問題,需要的朋友可以參考下

1 mountPath

mountPath是容器內(nèi)部文件系統(tǒng)的掛載點(diǎn)，它定義了容器內(nèi)部將外部存儲(chǔ)卷（如 PersistentVolume、ConfigMap、Secret 等）掛載到哪個(gè)路徑下。通過 mountPath，容器可以訪問這些掛載的數(shù)據(jù)或配置。

2 subPath

subPath 是 mountPath 下的子路徑，它允許容器將掛載的數(shù)據(jù)卷中的特定文件或目錄掛載到容器中的指定路徑下。這樣可以實(shí)現(xiàn)更加精細(xì)的文件系統(tǒng)級(jí)別的訪問控制。

3 mountPath使用場景

比如我需要?jiǎng)?chuàng)建一個(gè)nginx deployment，需要將自定義的nginx.conf配置文件獨(dú)立出來，作為一個(gè)configmap來掛載到pod中。

apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-config
data:
  my-nginx.conf: |
    server {
        listen       80;
        server_name  localhost;

        location / {
            root   /usr/share/nginx/html;
            index  index.html index.htm;
        }

        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   /usr/share/nginx/html;
        }
    }
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        volumeMounts:
        - name: nginx-config-volume
          mountPath: /etc/nginx/conf.d
      volumes:
      - name: nginx-config-volume
        configMap:
          name: nginx-config

部署完成后，你可以進(jìn)入pod，可以看到如下文件，這就是通過configmap掛載到容器中。

kubectl exec -it nginx-deployment-5b4699b7dd-fh4qc -- /bin/sh
# cd /etc/nginx/conf.d
# ls
my-nginx.conf

4 subPath使用場景

如果我想直接通過configmap定義/etc/nginx/nginx.conf，這時(shí)候如果還是只使用mountPath，就會(huì)有問題了。

apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-config
data:
  nginx.conf: |
    user  nginx;
    worker_processes  auto;

    error_log  /var/log/nginx/error.log notice;
    pid        /var/run/nginx.pid;


    events {
        worker_connections  1024;
    }


    http {
        include       /etc/nginx/mime.types;
        default_type  application/octet-stream;

        log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                          '$status $body_bytes_sent "$http_referer" '
                          '"$http_user_agent" "$http_x_forwarded_for"';

        access_log  /var/log/nginx/access.log  main;

        sendfile        on;
        #tcp_nopush     on;

        keepalive_timeout  65;

        #gzip  on;

        include /etc/nginx/conf.d/*.conf;
    }

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx
        volumeMounts:
        - name: nginx-config-volume
          mountPath: /etc/nginx
      volumes:
      - name: nginx-config-volume
        configMap:
          name: nginx-config

創(chuàng)建容器后，服務(wù)無法起來，會(huì)報(bào)錯(cuò)，因?yàn)榇藭r(shí)容器中的/etc/nginx/目錄會(huì)被我們掛載的configmap給覆蓋，所以原先/etc/nginx/目錄下的文件都無法被pod訪問，也就報(bào)錯(cuò)了。

2024/03/25 06:56:58 [emerg] 1#1: open() "/etc/nginx/mime.types" failed (2: No such file or directory) in /etc/nginx/nginx.conf:14
nginx: [emerg] open() "/etc/nginx/mime.types" failed (2: No such file or directory) in /etc/nginx/nginx.conf:14

那如果我將volumeMount改為如下配置呢，

      - name: nginx
        image: nginx
        volumeMounts:
        - name: nginx-config-volume
          mountPath: /etc/nginx/nginx.conf

此時(shí)原來/etc/nginx/目錄下的文件都不會(huì)受影響，但是依舊會(huì)報(bào)錯(cuò)，連容器都無法創(chuàng)建，

Error: failed to create containerd task: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: error during container init: error mounting "/var/lib/kubelet/pods/6755a0be-2f05-4edb-813b-ece2dcc2e8f1/volumes/kubernetes.io~configmap/nginx-config-volume" to rootfs at "/etc/nginx/nginx.conf": mount /var/lib/kubelet/pods/6755a0be-2f05-4edb-813b-ece2dcc2e8f1/volumes/kubernetes.io~configmap/nginx-config-volume:/etc/nginx/nginx.conf (via /proc/self/fd/6), flags: 0x5001: not a directory: unknown

這是因?yàn)榇藭r(shí)容器中/etc/nginx/nginx.conf這個(gè)路徑已經(jīng)是存在的，鏡像中默認(rèn)的文件，沒法作為mountpath使用。

當(dāng)然，你可以將nginx.conf換成其他名字，比如mynginx.conf，

      - name: nginx
        image: nginx
        volumeMounts:
        - name: nginx-config-volume
          mountPath: /etc/nginx/mynginx.conf

這樣就不會(huì)報(bào)錯(cuò)，但是這樣的效果是，容器中會(huì)創(chuàng)建一個(gè)目錄/etc/nginx/mynginx.conf/，這個(gè)目錄下有個(gè)文件nginx.conf，與最開始我們?cè)?etc/nginx/conf.d/定義my-nginx.conf一樣，但這并不是我們所要的。

kubectl exec -it nginx-deployment-6bf5f55df8-f452d -- /bin/sh
# cd /etc/nginx/mynginx.conf/
# ls
nginx.conf

這個(gè)時(shí)候，我們就需要使用subPath了，將volumeMount做如下修改，

      - name: nginx
        image: nginx
        volumeMounts:
        - name: nginx-config-volume
          mountPath: /etc/nginx/nginx.conf
          subPath: nginx.conf

這時(shí)服務(wù)就按照我們預(yù)期啟動(dòng)了，容器內(nèi)文件如下，而且nginx.conf的內(nèi)容就是我們configmap中定義的配置，

kubectl exec -it nginx-deployment-bb7d454c6-75bwz -- /bin/sh
# cd /etc/nginx/
# ls
conf.d	fastcgi_params	mime.types  modules  nginx.conf  scgi_params  uwsgi_params

類似的場景，比如需要在/etc/nginx/conf.d/為不同的host定義不同的配置，我們就可以創(chuàng)建多個(gè)configmap，配合使用subPath來掛載到同一個(gè)目錄下，

      - name: nginx
        image: nginx
        volumeMounts:
        - name: nginx-config-volume
          mountPath: /etc/nginx/conf.d/nginx.conf
          subPath: nginx.conf
        - name: my-nginx-config-volume
          mountPath: /etc/nginx/conf.d/my-nginx.conf
          subPath: my-nginx.conf

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