Docker是否构建--no-cache实际上下载并刷新基本映像？ [英] Does Docker build --no-cache actually download and refresh the base image?

问题描述

docker是否构建--no-cache刷新已更新远程基本映像？似乎没有指定文档。

Does docker build --no-cache refresh updated remote base images or not? Documentation does not seem to specify.

推荐答案

-无缓存选项将重建图像，而不使用本地缓存的图层。但是， FROM 行将重新使用已经拉出的基础映像（如果它已存在于构建主机上）（from行本身可能不会被缓存，但是它拉出的映像是缓存的）。如果要再次拉出基本映像，可以在build命令中使用-pull 选项。例如，

The --no-cache option will rebuild the image without using the local cached layers. However, the FROM line will reuse the already pulled base image if it exists on the build host (the from line itself may not be cached, but the image it pulls is). If you want to pull the base image again, you can use the --pull option to the build command. E.g.

$ docker build --no-cache --pull -t new-image-name:latest .

要查看build命令采用的所有选项，可以运行

To see all the options the build command takes, you can run

$ docker build --help

或在 https://docs.docker.com/engine/reference/命令行/生成/

以下是您可以自己测试此行为的示例：

Here's an example for how you can test this behavior yourself:

$ # very simple Dockerfile
$ cat df.test
FROM busybox:latest
RUN echo hello >test.txt

$ # pull an older version of busybox
$ docker pull busybox:1.29.2
1.29.2: Pulling from library/busybox
8c5a7da1afbc: Pull complete
Digest: sha256:cb63aa0641a885f54de20f61d152187419e8f6b159ed11a251a09d115fdff9bd
Status: Downloaded newer image for busybox:1.29.2

$ # retag that locally as latest
$ docker tag busybox:1.29.2 busybox:latest

$ # run the build, note the image id at the end of each build step
$ DOCKER_BUILDKIT=0 docker build --no-cache -f df.test .
Sending build context to Docker daemon  23.04kB
Step 1/2 : FROM busybox:latest
 ---> e1ddd7948a1c
Step 2/2 : RUN echo hello >test.txt
 ---> Running in dba83fef49f9
Removing intermediate container dba83fef49f9
 ---> 1f824ff05612
Successfully built 1f824ff05612

$ # rerun the build, note step 1 keeps the same id and never pulled a new latest
$ DOCKER_BUILDKIT=0 docker build --no-cache -f df.test .
Sending build context to Docker daemon  23.04kB
Step 1/2 : FROM busybox:latest
 ---> e1ddd7948a1c
Step 2/2 : RUN echo hello >test.txt
 ---> Running in 73df884b0f48
Removing intermediate container 73df884b0f48
 ---> e5870de6c24f
Successfully built e5870de6c24f

$ # run with --pull and see docker update the latest image, new container id from step 1
$ DOCKER_BUILDKIT=0 docker build --no-cache --pull -f df.test .
Sending build context to Docker daemon  23.04kB
Step 1/2 : FROM busybox:latest
latest: Pulling from library/busybox
Digest: sha256:2a03a6059f21e150ae84b0973863609494aad70f0a80eaeb64bddd8d92465812
Status: Downloaded newer image for busybox:latest
 ---> 59788edf1f3e
Step 2/2 : RUN echo hello >test.txt
 ---> Running in 7204116ecbf4
Removing intermediate container 7204116ecbf4
 ---> 2c6d8c48661b
Successfully built 2c6d8c48661b

$ # one last run now that busybox:latest is updated shows the pull has nothing to do
$ DOCKER_BUILDKIT=0 docker build --no-cache --pull -f df.test .
Sending build context to Docker daemon  23.04kB
Step 1/2 : FROM busybox:latest
latest: Pulling from library/busybox
Digest: sha256:2a03a6059f21e150ae84b0973863609494aad70f0a80eaeb64bddd8d92465812
Status: Image is up to date for busybox:latest
 ---> 59788edf1f3e
Step 2/2 : RUN echo hello >test.txt
 ---> Running in f37e19024e99
Removing intermediate container f37e19024e99
 ---> 044a5d4011c4
Successfully built 044a5d4011c4

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