我正在尝试设置一个 CI 构建，该构建从包含多步骤配置的 Dockerfile 构建映像。
以下是要求：
需要使用- Docker 层缓存，因为它在
RUN指令期间加载了大量应用依赖项。 - 它应该在每次构建后自动删除旧的悬空图像。(为防止以后
docker image prune手动清洗(
我的示例解决方案：
(只是为了演示问题(看起来像这样：
docker build -t sample-app.
docker rmi $(docker images --filter "dangling=true" -q --no-trunc)
Dockerfile：
FROM ubuntu:18.04 AS builder
WORKDIR /app
COPY some-file-for-build.txt /app
RUN echo 'building...'
FROM ubuntu:18.04
CMD ["echo", "running..."]
问题：
由于删除了悬空图像，缓存变得无效，并且在每次构建期间都会执行RUN指令。
单阶段配置的意外行为
但是，如果删除第二步，请将Dockerfile更改为：
FROM ubuntu:18.04
WORKDIR /app
COPY some-file-for-build.txt /app
RUN echo 'building...'
缓存将用于RUN指令。
Step 4/4 : RUN echo 'building...'
---> Using cache
---> 9c7c15230600
问题：
- 有没有办法让它按照要求工作？
- 为什么缓存适用于单阶段配置，但不适用于多阶段配置？
您需要
在 Docker 18.09 及更高版本上，还需要设置环境变量
DOCKER_BUILDKIT=1。此环境变量允许使用 BuildKit 功能，这反过来又允许更高性能的 docker 构建和缓存可能性，以减少构建时间。您可以在此处获取更多信息据我所知，缓存适用于使用
Docker >18.09的单阶段和多阶段配置。
Dockerfile：
FROM ubuntu:18.04 AS builder
WORKDIR /app
COPY some-file-for-build.txt /app
RUN echo 'building...'
FROM ubuntu:18.04
WORKDIR /app
COPY --from=builder /app/some-file-for-build.txt some-file-for-build-from-builder-stage.txt
CMD ["bash"]
以下是我的 docker 构建和清理日志：
> docker build --pull --rm -f "61977760.Dockerfile" -t 61977760:latest "."
[+] Building 4.7s (10/10) FINISHED
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [internal] load build definition from 61977760.Dockerfile 0.1s
=> => transferring dockerfile: 289B 0.0s
=> [internal] load metadata for docker.io/library/ubuntu:18.04 2.4s
=> [internal] load build context 0.0s
=> => transferring context: 44B 0.0s
=> [builder 1/4] FROM docker.io/library/ubuntu:18.04@sha256:3235326357dfb65f1781dbc4df3b834546d8bf914e82cce58e6e6b676e23ce8f 0.3s
=> => resolve docker.io/library/ubuntu:18.04@sha256:3235326357dfb65f1781dbc4df3b834546d8bf914e82cce58e6e6b676e23ce8f 0.0s
=> => sha256:3235326357dfb65f1781dbc4df3b834546d8bf914e82cce58e6e6b676e23ce8f 1.42kB / 1.42kB 0.0s
=> => sha256:b58746c8a89938b8c9f5b77de3b8cf1fe78210c696ab03a1442e235eea65d84f 1.15kB / 1.15kB 0.0s
=> => sha256:c3c304cb4f22ceb8a6fcc29a0cd6d3e4383ba9eb9b5fb552f87de7c0ba99edac 3.41kB / 3.41kB 0.0s
=> [builder 2/4] WORKDIR /app 0.0s
=> [builder 3/4] COPY some-file-for-build.txt /app 0.0s
=> [builder 4/4] RUN echo 'building...' 0.8s
=> [stage-1 3/3] COPY --from=builder /app/some-file-for-build.txt some-file-for-build-from-builder-stage.txt 0.0s
=> exporting to image 0.9s
=> => exporting layers 0.8s
=> => writing image sha256:94fd1e56c8044f0e2f80ee83c784cca5f2c384fd4eba9210f9ff81db68f406e5 0.0s
=> => naming to docker.io/library/61977760:latest 0.0s
> docker rmi $(docker images --filter "dangling=true" -q --no-trunc)
Deleted: sha256:4d157078805ccf08fd42502b19a665a0b60e80a33a7c5b6485e6fd201ca91cc1
Deleted: sha256:6f7f45cca948cf855afea76ff73878b8348da6ed2652d62b48f992f7d9768822
Deleted: sha256:eefe65e58b69e4567c5145828ec95d1d9f3477709cc76fb571e204920df8e378
> docker build --pull --rm -f "61977760.Dockerfile" -t 61977760:latest "."
[+] Building 0.9s (10/10) FINISHED
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [internal] load build definition from 61977760.Dockerfile 0.1s
=> => transferring dockerfile: 47B 0.0s
=> [internal] load metadata for docker.io/library/ubuntu:18.04 0.8s
=> [builder 1/4] FROM docker.io/library/ubuntu:18.04@sha256:3235326357dfb65f1781dbc4df3b834546d8bf914e82cce58e6e6b676e23ce8f 0.0s
=> [internal] load build context 0.0s
=> => transferring context: 42B 0.0s
=> CACHED [builder 2/4] WORKDIR /app 0.0s
=> CACHED [builder 3/4] COPY some-file-for-build.txt /app 0.0s
=> CACHED [builder 4/4] RUN echo 'building...' 0.0s
=> CACHED [stage-1 3/3] COPY --from=builder /app/some-file-for-build.txt some-file-for-build-from-builder-stage.txt 0.0s
=> exporting to image 0.0s
=> => exporting layers 0.0s
=> => writing image sha256:94fd1e56c8044f0e2f80ee83c784cca5f2c384fd4eba9210f9ff81db68f406e5 0.0s
=> => naming to docker.io/library/61977760:latest 0.0s
> docker builder prune --all
WARNING! This will remove all build cache. Are you sure you want to continue? [y/N] y
Deleted build cache objects:
np9zknowpkgi9aa2qtfstthnr
l0lucvc40nl98ceqxqadjplaw
elj14uwncgbk928oawwalht9x
s4l0w4h3day53tc3w20njd9cm
t6br3zadzcqhwilswvhkc2qkv
q8wrflxp3sppgmrft0yv805l0
qbe59a3kgjdvaw4ng7d5rasc8
sha256:82751c4dcc36265daceeee0abd938806b591eb66700863186377348c96e8aead
sha256:24b16cac34768092d57cdb429a12de6c9ee870a3724d70098a189ae0ac344c42
sha256:b1daff3b271fede2bec31812c398e28952f792935f608e467271cdfaccab7de2
sha256:b7f7d2967507ba709dbd1dd0426a5b0cdbe1ff936c131f8958c8d0f910eea19e
Total reclaimed space: 64.21MB
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