我有一个很大的docker图像A，我创建了一个新的Dockerfile
FROM A
RUN rm /big-folder
我试图使用以下内容构建图像：
docker build --squash -t B:latest .
图片大小是否应该减少/ big-folder目录的维度？
在我的实际测试中，图像A和B都保持相同的1,26 GB大小。
我做错了什么或者我没有理解壁球选项的实际行为？
答案 0 :(得分：0)
请注意，此功能是实验性的，因此可能会在将来的版本中发生变化。测试在版本17.03上完成。
根据我的测试，执行--squash会压缩仅在当前图像中添加的图层，而不会更改或合并任何FROM图像图层。
$ # squash-a is a sample base image like your image A
$ cat df.squash-a
FROM busybox:latest
ADD alpinetest.tgz /data
$ # squash-b is built off of squash-a, and uses the squash flag when built
$ cat df.squash-b
FROM test-squash-a:latest
RUN rm -rf /data
$ # squash-c merges the dockerfiles for A and B
$ cat df.squash-c
FROM busybox:latest
ADD alpinetest.tgz /data
RUN rm -rf /data
$ # standard build for A
$ docker build -f df.squash-a -t test-squash-a:latest .
Sending build context to Docker daemon 23.25 MB
Step 1/2 : FROM busybox:latest
---> 7968321274dc
Step 2/2 : ADD alpinetest.tgz /data
---> a417cffcd3d2
Removing intermediate container f15e9cd57375
Successfully built a417cffcd3d2
$ # build B with --squash
$ docker build -f df.squash-b --squash -t test-squash-b:latest .
Sending build context to Docker daemon 23.25 MB
Step 1/2 : FROM test-squash-a:latest
---> a417cffcd3d2
Step 2/2 : RUN rm -rf /data
---> Running in 961044b8ee10
---> f5939d65a51a
Removing intermediate container 961044b8ee10
Successfully built f5939d65a51a
$ # build C with --squash
$ docker build -f df.squash-c --squash -t test-squash-c:latest .
Sending build context to Docker daemon 23.25 MB
Step 1/3 : FROM busybox:latest
---> 7968321274dc
Step 2/3 : ADD alpinetest.tgz /data
---> Using cache
---> a417cffcd3d2
Step 3/3 : RUN rm -rf /data
---> Using cache
---> f5939d65a51a
Successfully built f5939d65a51a
$ # comparing images, A is large as expected, B didn't shrink, but C did
$ docker images | grep squash | sort
test-squash-a latest a417cffcd3d2 6 minutes ago 68 MB
test-squash-b latest 74e05f2130be 2 minutes ago 68 MB
test-squash-c latest 7562dac62351 2 minutes ago 1.11 MB
$ # start inspecting the layers with the busybox base
$ docker inspect -f '{{ .RootFS.Layers }}' busybox:latest
[sha256:38ac8d0f5bb30c8b742ad97a328b77870afaec92b33faf7e121161bc78a3fec8]
$ # layers in A adds one as expected
$ docker inspect -f '{{ .RootFS.Layers }}' test-squash-a
[sha256:38ac8d0f5bb30c8b742ad97a328b77870afaec92b33faf7e121161bc78a3fec8
sha256:3f4d2549e582599f3059fe3c869d4d353794b9064f8548c3a68629a4a93038d7]
$ # layers in B includes both busybox and A despite being squashed
$ docker inspect -f '{{ .RootFS.Layers }}' test-squash-b
[sha256:38ac8d0f5bb30c8b742ad97a328b77870afaec92b33faf7e121161bc78a3fec8
sha256:3f4d2549e582599f3059fe3c869d4d353794b9064f8548c3a68629a4a93038d7
sha256:68e9b1791c54b45c785c04440ba9de6eefd566a09890821296d46aec9609d2de]
$ # layers in C only adds a single layer on top of busybox despite 2 run commands
$ docker inspect -f '{{ .RootFS.Layers }}' test-squash-c
[sha256:38ac8d0f5bb30c8b742ad97a328b77870afaec92b33faf7e121161bc78a3fec8
sha256:5f70bf18a086007016e948b04aed3b82103a36bea41755b6cddfaf10ace3c6ef]
$ # the history output shows that the squash is over a range of layers
$ docker history test-squash-c
IMAGE CREATED CREATED BY SIZE COMMENT
7562dac62351 10 minutes ago 0 B merge sha256:f5939d65a51a45b9c30f71a53a878e42be3135a1e0696615aa3b34ed39e5dd99 to sha256:7968321274dc6b6171697c33df7815310468e694ac5be0ec03ff053bb135e768
<missing> 10 minutes ago /bin/sh -c rm -rf /data 0 B
<missing> 13 minutes ago /bin/sh -c #(nop) ADD file:8993cc512c40cc0... 0 B
<missing> 2 months ago /bin/sh -c #(nop) CMD ["sh"] 0 B
<missing> 2 months ago /bin/sh -c #(nop) ADD file:707e63805c0be1a... 1.11 MB