Exporting build artifacts

Export artifacts with Bake and consume them from .buildcharts/output.

Charts can export artifacts by writing files into /output inside the Dockerfile. The generated Bake plan then uses a local output to copy that content to .buildcharts/output/<type> on the host during docker buildx bake.

Output behavior by stage type

Stage type	Output behavior
build	type=cacheonly
docker	type=docker
Any other type	Export to .buildcharts/output/<type>

That means test, nuget, and any custom non-docker type export local files under .buildcharts/output.

How local exports work

BuildCharts implements local outputs using Docker Buildx Bake build artifact exports.

For any non-build and non-docker stage type, the generated docker-bake.hcl includes a local output like:

output = [
  "type=cacheonly,mode=max",
  "type=local,dest=.buildcharts/output/nuget"
]

type=local exports the filesystem contents of the target stage to a local directory. That means everything that exists in the final stage is copied to .buildcharts/output/<type>.

This is why charts that export artifacts typically use a final FROM scratch stage and copy only the artifacts into it, for example:

FROM scratch AS nuget
COPY --from=pre-nuget /output /

For the underlying Docker pattern, see Exporting build artifacts.

Work with Docker outputs

docker stages use type=docker, so the image is loaded into your Docker environment instead of being exported to .buildcharts/output/docker.

Use tags in build.yml so the result is easy to reference:

targets:
  src/App/App.csproj:
    - type: docker
      with:
        base: mcr.microsoft.com/dotnet/runtime:10.0
        tags: ["docker.io/example/app:${VERSION}-${COMMIT}"]

Dockerfile example

###################################
# Target: pre-sample
###################################
FROM build AS pre-sample

# The target source path, for example `src/MyApp/MyApp.csproj`
ARG BUILDCHARTS_SRC

# The generated target type, for example `build`
ARG BUILDCHARTS_TYPE

RUN echo "BUILDCHARTS_SRC=$BUILDCHARTS_SRC" && \
    echo "BUILDCHARTS_TYPE=$BUILDCHARTS_TYPE" && \
    mkdir -p /output && \
    echo "$BUILDCHARTS_SRC" > /output/source.txt && \
    echo "$BUILDCHARTS_TYPE" > /output/type.txt

###################################
# Target: sample
###################################
FROM scratch AS sample
COPY --from=pre-sample /output/source.txt /output/source.txt
COPY --from=pre-sample /output/type.txt /output/type.txt