【Docker】Dockerfile 之 VOLUME

参考教程：https://docs.docker.com/engine/reference/builder/

环境

1. virtual box 6.1
2. centos 7.8
3. docker 19.03

数据卷

VOLUME ["/data"]

The VOLUME instruction creates a mount point with the specified name and marks it as holding externally mounted volumes from native host or other containers. The value can be a JSON array, VOLUME ["/var/log/"], or a plain string with multiple arguments, such as VOLUME /var/log or VOLUME /var/log /var/db. For more information/examples and mounting instructions via the Docker client, refer to Share Directories via Volumes documentation.

VOLUME 指令创建具有指定名称的挂载点，并将其标记为保存来自本地主机或其他容器的外部安装的数据卷。该值可以是 JSON 数组，VOLUME ["/var/log/"]，也可以是带有多个参数的纯字符串，例如 VOLUME /var/log 或 VOLUME /var/log /var/db 。有关通过 Docker 客户端的更多挂载说明，请参考 Share Directories via Volumes 文档。

The docker run command initializes the newly created volume with any data that exists at the specified location within the base image. For example, consider the following Dockerfile snippet:

docker run 命令使用基础镜像内指定位置上存在的任何数据初始化新创建的卷。例如，考虑以下 Dockerfile 片段：

FROM ubuntu
RUN mkdir /myvol
RUN echo "hello world" > /myvol/greeting
VOLUME /myvol

This Dockerfile results in an image that causes docker run to create a new mount point at /myvol and copy the greeting file into the newly created volume.

这个 Dockerfile 生成一个镜像，该镜像使 docker run 在/myvol 目录创建一个新的挂载点，并将 greeting 文件复制到新创建的卷中。

关于指定卷的注意事项

Keep the following things in mind about volumes in the Dockerfile.
关于 Dockerfile 中的卷，请记住以下几点。

• Volumes on Windows-based containers: When using Windows-based containers, the destination of a volume inside the container must be one of:

• 基于 Windows 的容器上的卷：使用基于 Windows 的容器时，容器内卷的目的地必须是以下之一：

  • a non-existing or empty directory
  • a drive other than C:
  • 不存在或空目录
  • 除C：以外的驱动器

• Changing the volume from within the Dockerfile: If any build steps change the data within the volume after it has been declared, those changes will be discarded.

• 从 Dockerfile 内更改卷：如果在声明了卷后有任何构建步骤更改了卷中的数据，则这些更改将被丢弃。

• JSON formatting: The list is parsed as a JSON array. You must enclose words with double quotes (") rather than single quotes (').

• JSON 格式：该列表被解析为 JSON 数组。您必须用双引号（"）而不是单引号（'）括起单词。

• The host directory is declared at container run-time: The host directory (the mountpoint) is, by its nature, host-dependent. This is to preserve image portability, since a given host directory can’t be guaranteed to be available on all hosts. For this reason, you can’t mount a host directory from within the Dockerfile. The VOLUME instruction does not support specifying a host-dir parameter. You must specify the mountpoint when you create or run the container.

• 主机目录是在容器运行时声明的：主机目录（挂载点）从本质上说是依赖于主机的。这是为了保留镜像的可移植性，因为不能保证给定的主机目录在所有主机上都可用。因此，您无法从 Dockerfile 中挂载主机目录。VOLUME 指令不支持指定 host-dir 参数。创建或运行容器时，必须指定挂载点。

总结

介绍了 Dockerfile 中 VOLUME 指令的用法和注意事项。