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November 17, 2025 09:56
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GitLab CI YAML with Docker image build cache mount persistence
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| # Docker build cache mount persistence | |
| # | |
| # Usage: add `extends: .docker-build` to your Docker build CI job, and set | |
| # environment variable `DOCKER_CACHE_MOUNTS` to a comma-separated list of | |
| # build cache mount IDs, then use `--mount=type=cache,id=...,target=...` | |
| # in your Dockerfile | |
| # | |
| # Adapted from: https://github.com/reproducible-containers/buildkit-cache-dance | |
| # | |
| # See bottom for license | |
| .docker-build: | |
| image: docker:latest | |
| services: | |
| - docker:dind | |
| variables: | |
| DOCKER_DRIVER: overlay2 | |
| DOCKER_TLS_CERTDIR: /certs | |
| before_script: | |
| # Log in to GitLab container registry | |
| - echo "$CI_REGISTRY_PASSWORD" | |
| | docker login --password-stdin | |
| --username "$CI_REGISTRY_USER" | |
| "$CI_REGISTRY" | |
| # Inject Docker build cache mount | |
| - echo -e "\e[0Ksection_start:`date | |
| +%s`:inject-cache-mounts[collapsed=true]\r\e[0K\e[35;1mPopulate Docker | |
| build cache mounts\e[0m" | |
| # build Dockerfile | |
| - cacheInjectDockerfile='FROM alpine:latest' | |
| - | | |
| for name in $(ls .docker-cache-mounts || true); do | |
| echo "Populating Docker build cache mount: $name" | |
| cacheInjectDockerfile="$cacheInjectDockerfile | |
| RUN \ | |
| --mount=type=bind,source=.docker-cache-mounts/${name},target=/mnt/i \ | |
| --mount=type=cache,id=${name},target=/mnt/o \ | |
| echo '${name}:' && \ | |
| ls -A /mnt/i && \ | |
| cp -rp /mnt/i/* /mnt/o && \ | |
| ls -A /mnt/o" | |
| done | |
| - echo "$cacheInjectDockerfile" | |
| # build Docker image, discarding result (only care about build cache mount) | |
| - echo "$cacheInjectDockerfile" | docker build -f - -o - . > /dev/null | |
| || true | |
| - echo -e "\e[0Ksection_end:`date +%s`:inject-cache-mounts\r\e[0K" | |
| after_script: | |
| # Extract Docker build cache mount | |
| - echo -e "\e[0Ksection_start:`date | |
| +%s`:extract-cache-mounts[collapsed=true]\r\e[0K\e[35;1mSave Docker build | |
| cache mounts\e[0m" | |
| # build Dockerfile | |
| - cacheExtractDockerfile='FROM alpine:latest' | |
| - | | |
| for name in ${DOCKER_CACHE_MOUNTS//,/ }; do | |
| echo "Saving Docker build cache mount: $name" | |
| cacheExtractDockerfile="$cacheExtractDockerfile | |
| RUN \ | |
| --mount=type=cache,id=${name},target=/mnt/i \ | |
| echo '${name}:' && \ | |
| ls -A /mnt/i && \ | |
| mkdir -pv '/var/build-cache-extract/$name' && \ | |
| cp -rp /mnt/i/* '/var/build-cache-extract/$name' && \ | |
| ls '/var/build-cache-extract/$name'" | |
| done | |
| - cacheExtractImage="$CI_REGISTRY_IMAGE/build-cache-extract:$CI_COMMIT_SHORT_SHA" | |
| - echo "$cacheExtractDockerfile" | |
| # build Docker image | |
| - echo "$cacheExtractDockerfile" | |
| | docker build -f - -t "$cacheExtractImage" . | |
| # copy files out of Docker image | |
| - docker run --rm --volume "$CI_PROJECT_DIR/.docker-cache-mounts:/mnt/o" | |
| "$cacheExtractImage" | |
| ash -c 'cp -rp /var/build-cache-extract/* /mnt/o' | |
| - ls -A .docker-cache-mounts/* | |
| # remove Docker image | |
| - docker image rm "$cacheExtractImage" | |
| - echo -e "\e[0Ksection_end:`date +%s`:extract-cache-mounts\r\e[0K" | |
| cache: | |
| key: docker-build-cache | |
| paths: | |
| - .docker-cache-mounts | |
| # MIT License | |
| # | |
| # Copyright (c) 2025 Laurie O | |
| # | |
| # Permission is hereby granted, free of charge, to any person obtaining a copy | |
| # of this software and associated documentation files (the "Software"), to deal | |
| # in the Software without restriction, including without limitation the rights | |
| # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | |
| # copies of the Software, and to permit persons to whom the Software is | |
| # furnished to do so, subject to the following conditions: | |
| # | |
| # The above copyright notice and this permission notice shall be included in | |
| # all copies or substantial portions of the Software. | |
| # | |
| # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | |
| # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | |
| # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | |
| # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | |
| # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | |
| # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE | |
| # SOFTWARE. |
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