是 Dockerfile 中的 VOLUME 在 kubernetes 中持久化 [英] are VOLUME in Dockerfile persistent in kubernetes

问题描述

一些 Dockerfile 有一个 VOLUME 命令.

Some Dockerfile have a VOLUME command.

当这些容器部署在 Kubernetes 中，但没有提供 Kubernetes 卷时会发生什么:没有持久卷 (PV)，也没有持久卷声明 (PVC)?

What happens when such containers are deployed in Kubernetes, but no kubernetes volume are provided: no persistent volume (PV), nor persistent volume claim (PVC) ?

文件存储在哪里?

音量是否持久?

例如，Docker 的 library/postgreSQL 容器图像有:

For exemple, Dockerfile image for Docker's library/postgreSQL container image has:

    VOLUME /var/lib/postgresql/data

stable/postgresql helm图表不会总是创建 PV:

The stable/postgresql helm charts won't always create a PV:

kind: StatefulSet
### SNIP SNIP ###
      containers:
        - name: {{ template "postgresql.fullname" . }}
          image: {{ template "postgresql.image" . }}
### SNIP SNIP ###
          volumeMounts:
            {{ if .Values.persistence.enabled }}
            - name: data
              mountPath: {{ .Values.persistence.mountPath }}
              subPath: {{ .Values.persistence.subPath }}
{{- end }}
### SNIP SNIP ###
{{- if and .Values.persistence.enabled .Values.persistence.existingClaim }}
        - name: data
          persistentVolumeClaim:
{{- with .Values.persistence.existingClaim }}
            claimName: {{ tpl . $ }}
{{- end }}
{{- else if not .Values.persistence.enabled }}
        - name: data
          emptyDir: {}
{{- else if and .Values.persistence.enabled (not .Values.persistence.existingClaim) }}
  volumeClaimTemplates:
    - metadata:
        name: data
      {{- with .Values.persistence.annotations }}
        annotations:
        {{- range $key, $value := . }}
          {{ $key }}: {{ $value }}
        {{- end }}
      {{- end }}
      spec:
        accessModes:
        {{- range .Values.persistence.accessModes }}
          - {{ . | quote }}
        {{- end }}
        resources:
          requests:
            storage: {{ .Values.persistence.size | quote }}
        {{ include "postgresql.storageClass" . }}
{{- end }}

推荐答案

(根据我在 Rancher 2.4 中观察到的答案，kubernetes 1.17 使用 Docker)

(answer based on what I observed with Rancher 2.4, kubernetes 1.17 using Docker)

简答:

一个 Docker 卷在 /var/lib/docker/volumes/... 中创建，并在 Pod 停止或重新部署时删除.

a Docker volume is created in /var/lib/docker/volumes/... and removed when the pods is stopped or redeployed.

长答案:

Kubernetes 似乎对 Dockerfile 中容器/的体积一无所知.似乎没有创建任何 Kubernetes 对象.

Kubernetes doesn't seems to have any knowledge of the volume the containers / in the Dockerfile. No Kubernetes objects seems to be created.

当 Kubernetes 告诉 Docker 守护进程启动一个容器时，Docker 创建一个卷(如 docker volume create)并附加创建的卷(除非 kubernete 提供了一个卷来挂载).

When Kubernetes tell Docker daemon to start a container, Docker creates a volume (like docker volume create) and attach the created volume (unless kubernete's provides a volume to mount).

文件存储在哪里?

该文件是一个常规的 Docker 卷(参见下面的 docker 卷)

The file is a regular Docker volume (see docker volume below)

音量是否持久?

不，当 pod 被移除时，docker 卷也会被移除(就像你运行 docker rm $mycontainer --volumes)

No, the docker volume is removed when the pod is removed (like if you ran docker rm $mycontainer --volumes)

    docker inspect 6ce5f52186d4 | grep '"Driver": "local"' -A5 -B5

            {
                "Type": "volume",
                "Name": "679135a23430ceea6adb8d89e04c6baf9da33239a83ecb4c4ec3263e2c925d39",
                "Source": "/var/lib/docker/volumes/679135a23430ceea6adb8d89e04c6baf9da33239a83ecb4c4ec3263e2c925d39/_data",
                "Destination": "/var/lib/postgresql/data",
                "Driver": "local",
                "Mode": "",
                "RW": true,
                "Propagation": ""
            }

 $ docker volume ls
DRIVER              VOLUME NAME
local               679135a23430ceea6adb8d89e04c6baf9da33239a83ecb4c4ec3263e2c925d39

 $ du -hs /var/lib/docker/volumes/679135a23430ceea6adb8d89e04c6baf9da33239a83ecb4c4ec3263e2c925d39/
51.4M   /var/lib/docker/volumes/679135a23430ceea6adb8d89e04c6baf9da33239a83ecb4c4ec3263e2c925d39/

这篇关于是 Dockerfile 中的 VOLUME 在 kubernetes 中持久化的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！