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Containerfile: add chunked build target

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Add optional rechunker and chunked stages that use chunkah for
content-based layer splitting. This allows folding the splitting step
into the build step.

Through some build arg and redirection trickery, this leaves the
unchunked path functionally identical.

Assisted-by: OpenCode (Claude Opus 4.6)
This commit is contained in:
Jonathan Lebon 2026-03-26 22:33:31 -04:00
commit 0bf47996ec
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3 changed files with 36 additions and 6 deletions
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13
CONTRIBUTING.md
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@ -22,3 +22,16 @@ FEDORA_VERSION=43 just test # different Fedora version
BUILDER=podman just build # use podman instead of buildah
just ci # full CI run (validate + test all tiers)
```
## Building a split image
The Containerfile supports building a split (content-based layered)
image using [chunkah](https://github.com/coreos/chunkah) via the
`chunked` build target:
```bash
just build --chunkah
```
Extra arguments can be passed to chunkah via the `CHUNKAH_ARGS` build
arg (e.g. `BUILDER_EXTRA='--build-arg CHUNKAH_ARGS="--max-layers 128"' just build --chunkah`).

24
Containerfile
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@ -2,9 +2,11 @@
# nested containerization, so you must build with e.g.
# podman build --security-opt=label=disable --cap-add=all --device /dev/fuse <...>
# NOTE: This container build will output a single giant layer. It is strongly recommended
# to run the "rechunker" on the output of this build, see
# https://coreos.github.io/rpm-ostree/experimental-build-chunked-oci/
# NOTE: This container build will output a single giant layer. You can either
# run the "rechunker" on the output of this build (see bootc-base-imagectl.md),
# or build the split version directly with `just build --chunkah`
# (or if using podman/buildah directly, add `--build-arg FINAL=chunked
# --skip-unused-stages=false -v $PWD:/run/src`).
# Override this repos container to control the base image package versions. For
# example, podman build --from=quay.io/fedora/fedora:41 will get you a system
@ -14,8 +16,10 @@
# since konflux doesn't yet support --from.
ARG REPOS_IMAGE=quay.io/fedora/fedora:rawhide
ARG BUILDER_IMAGE=quay.io/fedora/fedora:rawhide
FROM $REPOS_IMAGE as repos
# Either 'unchunked' or 'chunked'. Determines whether we take the chunkah path.
ARG FINAL=unchunked
FROM $REPOS_IMAGE as repos
# BOOTSTRAPPING: This can be any image that has rpm-ostree, selinux-policy-targeted
# and python3 (for bootc-base-imagectl).
FROM $BUILDER_IMAGE as builder
@ -54,9 +58,19 @@ install -m 0755 -t /usr/libexec ./bootc-base-imagectl
EORUN
# This pulls in the rootfs generated in the previous step
FROM scratch
FROM scratch AS unchunked
COPY --from=builder /target-rootfs/ /
FROM builder AS rechunker
RUN dnf -y install chunkah
ARG CHUNKAH_ARGS=""
RUN --mount=from=unchunked,src=/,target=/chunkah,ro \
--mount=type=bind,target=/run/src,rw \
/usr/libexec/bootc-base-imagectl rechunk --chunkah ${CHUNKAH_ARGS} \
> /run/src/out.ociarchive
FROM oci-archive:out.ociarchive AS chunked
FROM $FINAL
LABEL containers.bootc 1
# This is an ad-hoc way for us to reference bootc-image-builder in
# a way that in theory client tooling can inspect and find. Today

5
Justfile
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@ -23,6 +23,7 @@ _build_cmd := builder + " build"
_tag := image + if tier == "standard" { "" } else { ":" + tier }
_base_image := "quay.io/fedora/fedora:" + fedora_version
_version_args := if fedora_version == "rawhide" { "" } else { "--build-arg=REPOS_IMAGE=" + _base_image + " --build-arg=BUILDER_IMAGE=" + _base_image }
_chunkah_args := "--build-arg FINAL=chunked --skip-unused-stages=false -v " + justfile_directory() + ":/run/src"
# ============================================================================
# Core targets
@ -30,10 +31,12 @@ _version_args := if fedora_version == "rawhide" { "" } else { "--build-arg=REPOS
# Build the container image
[group('core')]
build: _check-tier
[arg("chunkah", long, value="true")]
build chunkah="": _check-tier
{{_build_cmd}} -f Containerfile --no-cache \
-t {{_tag}} {{priv_args}} \
{{_version_args}} {{builder_extra}} \
{{if chunkah != "" { _chunkah_args } else { "" }}} \
--build-arg=MANIFEST=fedora-{{tier}} .
# Build and test