docker --cache-from 与 BUILDKIT_INLINE_CACHE 不是每两次都工作

Question

我正在尝试为我的 CI/CD 过程利用 BUILDKIT for Docker 的缓存/拉取系统。但它没有按预期工作。
我创建了一个虚拟的本地示例(但同样的情况也发生在我的 CI 系统 - AWS CodePipeline，以及 DockerHub 和 AWS ECR 中)。
Dockerfile:

# base image
FROM python:3.7-slim

# set working directory
WORKDIR /usr/src/app

# add and install requirements
RUN pip install --upgrade pip
COPY ./requirements.txt /usr/src/app/requirements.txt
RUN pip $PIP_PROXY install --no-cache-dir --compile -r requirements.txt

RUN echo 123
# add app
COPY ./run_test.py /usr/src/app/run_test.py

# run server
CMD ["python", "run_test.py"]

run_test.py 实际上并不有趣，但这里是代码以防万一:

import requests
import time

while True:
    time.sleep(1)
    print(requests)

您还需要创建一个空 requirements.txt文件在同一个文件夹中。
事先，我导出了两个环境变量:

export DOCKER_BUILDKIT=1  # to activate buildkit
export DUMMY_IMAGE_URL=bi0max/test_docker

然后，为了测试我有以下命令。前两个命令删除本地缓存以类似于 CI 环境，然后构建和推送。
小心，下面的代码会删除本地构建缓存:

docker builder prune -a -f && \
(docker image rm $DUMMY_IMAGE_URL:latest || true) && \
docker build \
--cache-from $DUMMY_IMAGE_URL:latest \
--build-arg BUILDKIT_INLINE_CACHE=1 \
--tag $DUMMY_IMAGE_URL:latest "." && \
docker push $DUMMY_IMAGE_URL:latest

正如预期的那样，第一次运行只是从头开始构建所有内容:

#2 [internal] load build definition from Dockerfile
#2 transferring dockerfile: 434B done
#2 DONE 0.0s

#1 [internal] load .dockerignore
#1 transferring context: 2B done
#1 DONE 0.1s

#3 [internal] load metadata for docker.io/library/python:3.7-slim
#3 DONE 0.0s

#12 [1/7] FROM docker.io/library/python:3.7-slim
#12 DONE 0.0s

#7 [internal] load build context
#7 DONE 0.0s

#4 importing cache manifest from bi0max/test_docker:latest
#4 ERROR: docker.io/bi0max/test_docker:latest not found

#12 [1/7] FROM docker.io/library/python:3.7-slim
#12 resolve docker.io/library/python:3.7-slim done
#12 DONE 0.0s

#7 [internal] load build context
#7 transferring context: 204B done
#7 DONE 0.1s

#5 [2/7] WORKDIR /usr/src/app
#5 DONE 0.0s

#6 [3/7] RUN pip install --upgrade pip
#6 1.951 Requirement already up-to-date: pip in /usr/local/lib/python3.7/site-packages (20.1.1)
#6 DONE 2.3s

#8 [4/7] COPY ./requirements.txt /usr/src/app/requirements.txt
#8 DONE 0.0s

#9 [5/7] RUN pip $PIP_PROXY install --no-cache-dir --compile -r requirement...
#9 0.750 Collecting requests==2.22.0
#9 0.848   Downloading requests-2.22.0-py2.py3-none-any.whl (57 kB)
#9 0.932 Collecting idna<2.9,>=2.5
#9 0.948   Downloading idna-2.8-py2.py3-none-any.whl (58 kB)
#9 0.995 Collecting chardet<3.1.0,>=3.0.2
#9 1.011   Downloading chardet-3.0.4-py2.py3-none-any.whl (133 kB)
#9 1.135 Collecting urllib3!=1.25.0,!=1.25.1,<1.26,>=1.21.1
#9 1.153   Downloading urllib3-1.25.9-py2.py3-none-any.whl (126 kB)
#9 1.264 Collecting certifi>=2017.4.17
#9 1.282   Downloading certifi-2020.4.5.1-py2.py3-none-any.whl (157 kB)
#9 1.378 Installing collected packages: idna, chardet, urllib3, certifi, requests
#9 1.916 Successfully installed certifi-2020.4.5.1 chardet-3.0.4 idna-2.8 requests-2.22.0 urllib3-1.25.9
#9 DONE 2.2s

#10 [6/7] RUN echo 123
#10 0.265 123
#10 DONE 0.3s

#11 [7/7] COPY ./run_test.py /usr/src/app/run_test.py
#11 DONE 0.0s

#13 exporting to image
#13 exporting layers done
#13 writing image sha256:f98327afae246096725f7e54742fe9b25079f1b779699b099e66c8def1e19052 done
#13 naming to docker.io/bi0max/test_docker:latest done
#13 DONE 0.0s

#14 exporting cache
#14 preparing build cache for export done
#14 DONE 0.0s

然后，我稍微调整了一下run_test.py文件，结果再次符合预期。直到最后一步([7/7] COPY)的所有层都从存储库下载并重新使用。

#2 [internal] load .dockerignore
#2 transferring context: 2B done
#2 DONE 0.0s

#1 [internal] load build definition from Dockerfile
#1 transferring dockerfile: 434B done
#1 DONE 0.1s

#3 [internal] load metadata for docker.io/library/python:3.7-slim
#3 DONE 0.0s

#8 [internal] load build context
#8 DONE 0.0s

#4 [1/7] FROM docker.io/library/python:3.7-slim
#4 DONE 0.0s

#5 importing cache manifest from bi0max/test_docker:latest
#5 DONE 1.2s

#8 [internal] load build context
#8 transferring context: 193B done
#8 DONE 0.0s

#6 [2/7] WORKDIR /usr/src/app
#6 CACHED

#7 [3/7] RUN pip install --upgrade pip
#7 CACHED

#9 [4/7] COPY ./requirements.txt /usr/src/app/requirements.txt
#9 CACHED

#10 [5/7] RUN pip $PIP_PROXY install --no-cache-dir --compile -r requirement...
#10 CACHED

#11 [6/7] RUN echo 123
#11 pulling sha256:79fc69c08b391d082b4d2617faed489d220444fa0cf06953cdff55c667866bed
#11 pulling sha256:071624272167ab4e35a30eb1640cb3f15ced19c6cd10fa1c9d49763372e81c23
#11 pulling sha256:04ed4ecd76e1a110f468eb1a3173bbfa578c6b4c85a6dc82bf4a489ed8b8c54d
#11 pulling sha256:79fc69c08b391d082b4d2617faed489d220444fa0cf06953cdff55c667866bed 0.2s done
#11 pulling sha256:d6406c1ce2dc5e841233ebce164ee469388102cb98f1473adaeca15455d6d797
#11 pulling sha256:071624272167ab4e35a30eb1640cb3f15ced19c6cd10fa1c9d49763372e81c23 0.5s done
#11 pulling sha256:04ed4ecd76e1a110f468eb1a3173bbfa578c6b4c85a6dc82bf4a489ed8b8c54d 0.5s done
#11 pulling sha256:4f4fb700ef54461cfa02571ae0db9a0dc1e0cdb5577484a6d75e68dc38e8acc1
#11 pulling sha256:d6406c1ce2dc5e841233ebce164ee469388102cb98f1473adaeca15455d6d797 0.3s done
#11 pulling sha256:4f4fb700ef54461cfa02571ae0db9a0dc1e0cdb5577484a6d75e68dc38e8acc1 0.2s done
#11 CACHED

#12 [7/7] COPY ./run_test.py /usr/src/app/run_test.py
#12 DONE 0.0s

#13 exporting to image
#13 exporting layers done
#13 writing image sha256:f37692114f10b9a3646203569a0849af20774651f4aa0f5dc8d6f133fb7ff062 done
#13 naming to docker.io/bi0max/test_docker:latest done
#13 DONE 0.0s

#14 exporting cache
#14 preparing build cache for export done
#14 DONE 0.0s

现在，我换 run_test.py再次，我希望 docker 做与上次相同的事情。但我得到以下结果，它从头开始构建所有内容:

#1 [internal] load .dockerignore
#1 transferring context: 2B done
#1 DONE 0.0s

#2 [internal] load build definition from Dockerfile
#2 transferring dockerfile: 434B done
#2 DONE 0.0s

#3 [internal] load metadata for docker.io/library/python:3.7-slim
#3 DONE 0.0s

#5 [1/7] FROM docker.io/library/python:3.7-slim
#5 DONE 0.0s

#8 [internal] load build context
#8 DONE 0.0s

#4 importing cache manifest from bi0max/test_docker:latest
#4 DONE 1.7s

#8 [internal] load build context
#8 transferring context: 182B done
#8 DONE 0.0s

#5 [1/7] FROM docker.io/library/python:3.7-slim
#5 resolve docker.io/library/python:3.7-slim done
#5 DONE 0.1s

#6 [2/7] WORKDIR /usr/src/app
#6 DONE 0.0s

#7 [3/7] RUN pip install --upgrade pip
#7 1.774 Requirement already up-to-date: pip in /usr/local/lib/python3.7/site-packages (20.1.1)
#7 DONE 2.1s

#9 [4/7] COPY ./requirements.txt /usr/src/app/requirements.txt
#9 DONE 0.0s

#10 [5/7] RUN pip $PIP_PROXY install --no-cache-dir --compile -r requirement...
#10 0.805 Collecting requests==2.22.0
#10 0.905   Downloading requests-2.22.0-py2.py3-none-any.whl (57 kB)
#10 1.079 Collecting urllib3!=1.25.0,!=1.25.1,<1.26,>=1.21.1
#10 1.109   Downloading urllib3-1.25.9-py2.py3-none-any.whl (126 kB)
#10 1.242 Collecting certifi>=2017.4.17
#10 1.259   Downloading certifi-2020.4.5.1-py2.py3-none-any.whl (157 kB)
#10 1.336 Collecting idna<2.9,>=2.5
#10 1.353   Downloading idna-2.8-py2.py3-none-any.whl (58 kB)
#10 1.410 Collecting chardet<3.1.0,>=3.0.2
#10 1.428   Downloading chardet-3.0.4-py2.py3-none-any.whl (133 kB)
#10 1.545 Installing collected packages: urllib3, certifi, idna, chardet, requests
#10 2.102 Successfully installed certifi-2020.4.5.1 chardet-3.0.4 idna-2.8 requests-2.22.0 urllib3-1.25.9
#10 DONE 2.4s

#11 [6/7] RUN echo 123
#11 0.259 123
#11 DONE 0.3s

#12 [7/7] COPY ./run_test.py /usr/src/app/run_test.py
#12 DONE 0.0s

#13 exporting to image
#13 exporting layers done
#13 writing image sha256:f4ffb0e84e334b4b35fe2504de11012e5dc1ca5978eace055932e9bbbe83c93e done
#13 naming to docker.io/bi0max/test_docker:latest done
#13 DONE 0.0s

#14 exporting cache
#14 preparing build cache for export done
#14 DONE 0.0s

但对我来说最奇怪的是，当我改变时run_test.py第三次，它再次使用缓存图层。它以同样的方式继续:第四次 - 不使用，第五次 - 使用，等等......
我在这里想念什么吗？
如果我每次在构建之前拉取图像，那么它总是使用缓存，但它也可以在没有 BUILDKIT 的情况下以相同的方式工作。

Answer 1

这个问题在较新的 docker 版本中得到修复，一个简单的升级就解决了这个问题。
否则，GitHub 上描述的解决方案可以帮助不依赖系统 docker 版本:https://github.com/moby/buildkit/issues/1981#issuecomment-785534131