Dockerfile examples for reproducing package cache (e.g., /etc/apk/cache)

This repo contains Dockerfile examples to reproduce package cache with specific versions, by pushing the cache to an image registry.

See Dockerfile.alpine:

ARG PACKAGES="gcc neofetch"

# PKG_CACHE defaults to the "pkg-cache-local" stage in this image.
# Can be overridden to a custom image for reproducible builds.
ARG PKG_CACHE=pkg-cache-local

ARG BASE=alpine:3.18.3@sha256:7144f7bab3d4c2648d7e59409f15ec52a18006a128c733fcff20d3a4a54ba44a

FROM ${BASE} AS base

FROM base AS pkg-cache-local-base
ARG PACKAGES
RUN mkdir -p /etc/apk/cache && \
  apk update && \
  apk cache download --available --add-dependencies ${PACKAGES}

FROM scratch AS pkg-cache-local
COPY --from=pkg-cache-local-base /etc/apk/cache /etc/apk/cache

# pkg-cache is the stage to collect package cache files.
# This stage can be pushed for the sake of reproducible builds.
FROM ${PKG_CACHE} AS pkg-cache

FROM base
ARG PACKAGES
RUN \
  --mount=from=pkg-cache,source=/etc/apk/cache,target=/etc/apk/cache,rw \
  --network=none \
  apk add --no-network ${PACKAGES}
# The package signatures are verified by apk

Push:

docker build . -f Dockerfile.alpine \
  --push -t example.com/example-alpine:v1.2.3

docker build . -f Dockerfile.alpine \
  --push -t example.com/example-alpine:v1.2.3-pkg-cache \
  --target pkg-cache

Repro:

docker build . -f Dockerfile.alpine \
  -t example-alpine:v1.2.3 \
  --build-arg PKG_CACHE=example.com/example-alpine:v1.2.3-pkg-cache

Other examples:

• Dockerfile.archlinux: ArchLinux (:warning: Discouraged. See the WARNING at the end of the file)
• Dockerfile.debian: Debian and Ubuntu (:warning: Discouraged. See the WARNING at the end of the file)
• Dockerfile.fedora: Fedora, CentOS Stream, Rocky Linux, and AlmaLinux
• Dockerfile.opensuse: openSUSE

Related project

https://github.com/reproducible-containers/repro-sources-list.sh configures /etc/apt/sources.list and similar files for installing packages from a past snapshot like http://snapshot.debian.org/archive/debian/20230101T000000Z.

Project	Cache location	Best for
https://github.com/reproducible-containers/repro-sources-list.sh	Distros' permanent snapshot servers (*1)	Debian, Ubuntu, ArchLinux
https://github.com/reproducible-containers/repro-pkg-cache	Your own permanent image registry	Alpine, Fedora, Rocky, openSUSE, etc.

(*1): The packages can be also ephemerally cached on GitHub Actions to reduce loads on distros' snapshot servers. See https://github.com/reproducible-containers/buildkit-cache-dance.

Alternatives

• There is a proposal by Tõnis Tiigi to extend BuildKit to attach package materials to an image provenance. See his comment on 2023-09-15 in moby/buildkit#4238.