Should the github workflow use buildkit-cache-dance?

[slingshotsys]

In the Dockerfile examples, --mount=type=cache,target=/root/.cache/uv is used. According to the Docker docs, cache mounts don't persist across GitHub Actions runs.

Should ci.yaml be updated to use buildkit-cache-dance, or does the uv cache work some other way?

[genevieve-me]

For what it's worth, I've been building my images with --volume "$UV_CACHE_DIR:/uv-cache:Z" and sharing the same CI cache which is used for other jobs (eg tests) and it's been working well.

Edited to add example:

# --- Builder Stage ---
FROM ghcr.io/astral-sh/uv:0.8.15-python3.13-trixie-slim AS builder

ENV UV_COMPILE_BYTECODE=1 UV_LINK_MODE=copy UV_PYTHON_DOWNLOADS=0
# we don't use a --mount=type=cache because that can't easily be cached on ephemeral runners
# it requires workarounds like https://github.com/reproducible-containers/buildkit-cache-dance
# instead, we can just mount the shared CI cache into the build
ENV UV_CACHE_DIR=/uv-cache
WORKDIR /app

# Install dependencies
# no-install-local implies --no-install-workspace and --no-install-project
# we use --frozen because --locked wants to compare with pyproject.toml of all workspace members
# see: https://github.com/astral-sh/uv/issues/6685
# uv needs pyproject.toml mounted
# see: https://github.com/astral-sh/uv/issues/6573
RUN --mount=type=bind,source=uv.lock,target=uv.lock \
    --mount=type=bind,source=pyproject.toml,target=pyproject.toml \
    uv sync --package example --frozen --no-install-local --no-editable --no-dev
ADD . /app
RUN uv sync --package example --locked --no-editable --no-dev

# --- Final Stage ---
FROM python:3.13-slim

WORKDIR /app

COPY --from=builder /app/.venv ./.venv

RUN useradd --create-home appuser
USER appuser

# Script entrypoint from punchy-rss pyproject.toml
CMD ["/app/.venv/bin/example", "--some-arg"]

and in our build scripts (running in GitLab CI):

APP_NAME="$(basename "${APP_PATH}")"
APP_SLUG="$(echo "${APP_NAME}" | tr '[:upper:]' '[:lower:]' | sed -E 's/[_[:space:]]+/-/g')"
REPO_NAME="some-apps/${APP_SLUG}"
IMAGE_URI="${ECR_REGISTRY_URL}/${REPO_NAME}:${CI_COMMIT_SHORT_SHA}"
CONTAINERFILE="${APP_PATH}/Containerfile"

buildah bud --layers --cache-from "${CI_REGISTRY_IMAGE}/${APP_SLUG}-cache" --cache-to "${CI_REGISTRY_IMAGE}/${APP_SLUG}-cache" --volume "$UV_CACHE_DIR:/uv-cache:Z" -t "${IMAGE_URI}" -f "${CONTAINERFILE}"