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Merged
modem7 merged 3 commits into from
Jun 27, 2026
Merged

Improve Dockerfile layer caching #239

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a219ff8
Reorder Dockerfile layers for better cache utilisation
modem7 Jun 27, 2026
b5c24cb
Add hadolint inline ignores for Dockerfile layer reorder
modem7 Jun 27, 2026
7bb35bf
Add missing hadolint inline ignores (DL3006, DL3018)
modem7 Jun 27, 2026
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7 changes: 7 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -3,6 +3,13 @@ All notable changes to this project will be documented in this file.

The format is based on [Keep a Changelog](http://keepachangelog.com/).

## 2026-06-27 (continued 7)

### Changed

- Reorder Dockerfile layers for better cache utilisation: `apk` packages now install before S6 overlay is added, and S6 is extracted in its own `RUN` step. Previously a S6 version bump invalidated the entire apk + pip chain; now each concern caches independently.
- Use `--mount=type=cache,id=apk-${TARGETARCH}` for the `apk` step (consistent with the existing pip cache mount).

## 2026-06-27 (continued 6)

### Fixed
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63 changes: 34 additions & 29 deletions Dockerfile
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Expand Up @@ -14,46 +14,35 @@
FROM base AS base-arm64
ENV S6_OVERLAY_ARCH=aarch64

# hadolint ignore=DL3006
FROM base-${TARGETARCH}${TARGETVARIANT}

ARG S6_OVERLAY_VERSION=3.2.3.0

# Add S6 Overlay
ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-${S6_OVERLAY_ARCH}.tar.xz /tmp/s6-overlay.tar.xz
ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-noarch.tar.xz /tmp

# Add S6 optional symlinks
ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-symlinks-noarch.tar.xz /tmp
ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-symlinks-arch.tar.xz /tmp

ENV LANG='en_US.UTF-8' \
LANGUAGE='en_US.UTF-8' \
S6_LOGGING="1" \
S6_VERBOSITY="0" \
S6_CMD_WAIT_FOR_SERVICES_MAXTIME="0" \
TZ="Europe/London"

RUN <<EOF
set -xe
apk upgrade --update --no-cache
tar -C / -Jxpf /tmp/s6-overlay.tar.xz
tar -C / -Jxpf /tmp/s6-overlay-noarch.tar.xz
tar -C / -Jxpf /tmp/s6-overlay-symlinks-noarch.tar.xz
tar -C / -Jxpf /tmp/s6-overlay-symlinks-arch.tar.xz
rm -rf /tmp/*.tar.xz

apk add --no-cache -U \
bash \
bash-completion \
btrfs-progs \
ca-certificates \
curl \
findmnt \
fuse \
acl-libs \
libxxhash \
logrotate \
lz4-libs \
# Install system packages first — this layer is independent of S6 and borgmatic
# versions, so it stays cached across S6 bumps and requirements.txt changes.
# hadolint ignore=DL3005,DL3018,DL3019,DL3059
RUN --mount=type=cache,id=apk-${TARGETARCH},target=/etc/apk/cache \
apk upgrade -U && \
apk add -U \
bash \
bash-completion \
btrfs-progs \
ca-certificates \
curl \
findmnt \
fuse \
acl-libs \
libxxhash \
logrotate \
lz4-libs \
mariadb-client \
mariadb-connector-c \
mongodb-tools \
Expand All @@ -63,11 +52,27 @@
sqlite \
tzdata \
xxhash

# hadolint ignore=DL3059
# Add S6 Overlay — separate layer so S6 bumps don't invalidate the apk layer
ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-${S6_OVERLAY_ARCH}.tar.xz /tmp/s6-overlay.tar.xz
ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-noarch.tar.xz /tmp
ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-symlinks-noarch.tar.xz /tmp
ADD https://github.com/just-containers/s6-overlay/releases/download/v${S6_OVERLAY_VERSION}/s6-overlay-symlinks-arch.tar.xz /tmp

# hadolint ignore=DL3059
RUN <<EOF
set -xe
tar -C / -Jxpf /tmp/s6-overlay.tar.xz
tar -C / -Jxpf /tmp/s6-overlay-noarch.tar.xz
tar -C / -Jxpf /tmp/s6-overlay-symlinks-noarch.tar.xz
tar -C / -Jxpf /tmp/s6-overlay-symlinks-arch.tar.xz
rm -rf /tmp/*.tar.xz
EOF

COPY --link requirements.txt /

RUN --mount=type=cache,id=pip,target=/root/.cache,sharing=locked \

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GitHub Actions / Lint 

DL3042 style: Avoid use of cache directory with pip. Use `pip install --no-cache-dir <package>`

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GitHub Actions / Lint 

DL3018 style: Pin versions in apk add. Instead of `apk add <package>` use `apk add <package>=<version>`

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GitHub Actions / Lint 

DL3013 style: Pin versions in pip. Instead of `pip install <package>` use `pip install <package>==<version>` or `pip install --requirement <requirements file>`

Check failure on line 75 in Dockerfile

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GitHub Actions / Lint 

DL3042 style: Avoid use of cache directory with pip. Use `pip install --no-cache-dir <package>`

Check failure on line 75 in Dockerfile

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GitHub Actions / Lint 

DL3018 style: Pin versions in apk add. Instead of `apk add <package>` use `apk add <package>=<version>`

Check failure on line 75 in Dockerfile

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GitHub Actions / Lint 

DL3013 style: Pin versions in pip. Instead of `pip install <package>` use `pip install <package>==<version>` or `pip install --requirement <requirements file>`
<<EOF
set -xe
python3 -m pip install -U pip
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