为什么要缓存层RUN命令无效？
FROM python:3.7-slim
ARG VERSION
RUN pip install --upgrade pip && pip install -r requirements.txt
ENV VERSION_2 2
ENV VERSION $VERSION
CMD ["env"]
如上面的dockerfile所示，使用build arg动态设置环境变量会导致RUN的缓存层指令变得无效，因为build-arg每次构建都会改变，镜像的历史如下
IMAGE CREATED CREATED BY SIZE COMMENT
13d8c1c91aed 2 minutes ago CMD ["env"] 0B buildkit.dockerfile.v0
<missing> 2 minutes ago ENV VERSION=1 0B buildkit.dockerfile.v0
<missing> 2 minutes ago ENV VERSION_2=2 0B buildkit.dockerfile.v0
<missing> 2 minutes ago RUN |1 VERSION=1 /bin/sh -c pip install --up… 5.28MB buildkit.dockerfile.v0
<missing> 2 minutes ago ARG VERSION 0B buildkit.dockerfile.v0
<missing> 7 days ago /bin/sh -c #(nop) CMD ["python3"] 0B
<missing> 7 days ago /bin/sh -c set -ex; savedAptMark="$(apt-ma… 8.49MB
<missing> 7 days ago /bin/sh -c #(nop) ENV PYTHON_GET_PIP_SHA256… 0B
<missing> 7 days ago /bin/sh -c #(nop) ENV PYTHON_GET_PIP_URL=ht… 0B
<missing> 7 days ago /bin/sh -c #(nop) ENV PYTHON_PIP_VERSION=20… 0B
<missing> 7 days ago /bin/sh -c cd /usr/local/bin && ln -s idle3… 32B
<missing> 7 days ago /bin/sh -c set -ex && savedAptMark="$(apt-… 27.1MB
<missing> 7 days ago /bin/sh -c #(nop) ENV PYTHON_VERSION=3.7.9 0B
<missing> 7 days ago /bin/sh -c #(nop) ENV GPG_KEY=0D96DF4D4110E… 0B
<missing> 7 days ago /bin/sh -c set -eux; apt-get update; apt-g… 7.03MB
<missing> 8 days ago /bin/sh -c #(nop) ENV LANG=C.UTF-8 0B
<missing> 8 days ago /bin/sh -c #(nop) ENV PATH=/usr/local/bin:/… 0B
<missing> 8 days ago /bin/sh -c #(nop) CMD ["bash"] 0B
<missing> 8 days ago /bin/sh -c #(nop) ADD file:422aca8901ae3d869… 69.2MB
最佳答案
docker 文档有明确的解释，好吧，我粗心了。
https://docs.docker.com/engine/reference/builder/#impact-on-build-caching
关于docker - 在 Dockerfile 中使用 env 和 arg 会导致缓存层无效，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/65813457/