码头工人图像共享相同的图层吗？ [英] Do docker images share identical layers?

问题描述

我知道每个容器都是一个图像，在一堆只读层之上具有一个可读/可写层，并且多个容器可以共享该图像的只读层。

I know that each container is an image with a readable/writeable layer on top of a bunch of read-only layers, and that multiple containers can share the read-only layers of the image. Do two images that were created from the same base image share their identical images?

示例：

• 图像A具有相同的基本图像吗？ 5层，重1GB。


• 以A作为基本图像创建图像B，然后添加另一层并重1.1GB。


• 图像C为以A作为基本映像创建并添加了另一层并重1.5GB

磁盘总空间现在是3.6GB还是1.6GB？

Is the total disk space now 3.6GB or 1.6GB?

推荐答案

简短答案： 1.6GB

您可以执行以下有趣的实验：

This is an interesting experiment that you can perform:

拉虚拟图像：

docker pull alpine

为子映像准备Dockerfile alpine （这里我使用 dd 在图像中创建了10MB的文件）

Prepare a Dockerfile for a child image alpine(here I created a 10MB file in the image using dd)

FROM alpine
RUN dd if=/dev/zero of=file.txt count=10000 bs=1024

建立子图片

docker build -t alpine-plus-ten-mb .

然后检查这两个图像并查看图层。

Then inspect the two images and have a look at the layers.

• 下层目录可以是只读的，也可以是覆盖本身。


• 上层目录通常是可写的。


• 合并的目录是上层和下层之间的统一视图


• 工作目录用于在文件在层之间切换时准备文件。

• The lower directory can be read-only or could be an overlay itself.
• The upper directory is normally writable.
• The merged directory is the unified view between upper and lower
• The work directory is used to prepare files as they are switched between the layers.

docker image inspect --format='{{json .GraphDriver.Data}}' alpine
{
    "MergedDir": "/var/lib/docker/overlay2/0654e44ddf13ebd2a0feb2ac6261e62f6c83a8be1937a71c544f69eb6208d93b/merged",
    "UpperDir": "/var/lib/docker/overlay2/0654e44ddf13ebd2a0feb2ac6261e62f6c83a8be1937a71c544f69eb6208d93b/diff",
    "WorkDir": "/var/lib/docker/overlay2/0654e44ddf13ebd2a0feb2ac6261e62f6c83a8be1937a71c544f69eb6208d93b/work"
}

docker image inspect --format='{{json .GraphDriver.Data}}' alpine-plus-ten-mb
{
    "LowerDir": "/var/lib/docker/overlay2/0654e44ddf13ebd2a0feb2ac6261e62f6c83a8be1937a71c544f69eb6208d93b/diff",
    "MergedDir": "/var/lib/docker/overlay2/5ca936630339967105c28d4d8c9669d99f0f449a307c43c09d60f6341cf56271/merged",
    "UpperDir": "/var/lib/docker/overlay2/5ca936630339967105c28d4d8c9669d99f0f449a307c43c09d60f6341cf56271/diff",
    "WorkDir": "/var/lib/docker/overlay2/5ca936630339967105c28d4d8c9669d99f0f449a307c43c09d60f6341cf56271/work"
}

读取 d93b / diff 层-仅用于我们的子图像 alpine-plus-ten-mb 。

而且，所有这些都可以在主机系统上进行浏览。这是〜10MB delta ，是我在构建子图像时与 dd 人为添加的。

The layer d93b/diff is read-only for our child image alpine-plus-ten-mb.
More over, all of these can be explored on the host system. Here is the ~10MB delta that I artificially added with dd when I built the child image.

sudo du -sh "/var/lib/docker/overlay2/5ca936630339967105c28d4d8c9669d99f0f449a307c43c09d60f6341cf56271/diff"
9.8M    /var/lib/docker/overlay2/5ca936630339967105c28d4d8c9669d99f0f449a307c43c09d60f6341cf56271/diff

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