Docker是否构建--实际上没有缓存下载并刷新基本映像？

Question

docker是否构建--无缓存刷新更新的远程基本映像？文档似乎没有具体说明。

Answer 1

--没有缓存会在不使用缓存的情况下重建图像，因此它本质上是一个干净的构建。

根据帮助docker build--help--no cache在构建映像时不要使用cache

Answer 2

docker build（docker构建）--没有缓存将在不重用缓存层的情况下重建整个映像，但它不会从远程存储库中提取最新的基本映像。它将只使用本地存储的图像。

Answer 3

“无缓存”选项将在不使用本地缓存层的情况下重建图像。但是，如果已提取的基本映像存在于生成主机上，则“发件人”行将重用该基本映像（发件人行本身可能不会被缓存，但它提取的映像会被缓存）。如果要再次拉取基础图像，可以使用build命令的“拉”（pull）选项。例如。

$ 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

$ docker build --help

或参见https://docs.docker.com/engine/reference/commandline/build/

以下是一个如何自己测试此行为的示例：

$ # 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