Reduce size of images that are based on jit snapshots

[mnordine]

I have a long-running server that has code that runs slow when compiled AOT, and I want to optimize startup time and reduce the image size. I've tried doing the following:

FROM dart:2.17 AS build

WORKDIR /app
COPY pubspec.yaml .
RUN dart pub get

COPY . .
RUN dart pub get --offline
RUN dart compile jit-snapshot bin/server.dart

FROM scratch
COPY --from=build /runtime/ /
COPY --from=build /app/bin/server.jit app/bin/
EXPOSE 4002
ENTRYPOINT ["dart", "/app/bin/server.jit"]

However, I get an error when I try to run the container, because dart is not found. Is there any way this could work, similar to AOT?

Using something like this

FROM dart:2.17

WORKDIR /app

COPY bin/server.jit /app/bin/
ENTRYPOINT ["dart", "bin/server.jit"]

results in a 266.8MB image(!)

[cpswan]

Have you tried copying just dart into your FROM scratch container so that it can be found (making sure it's somewhere on the PATH)?

It's possible that you'll then run into other missing dependencies (as the runtime is intended for AOT binaries), but it might just work.

[mnordine]

Any idea where the dart binary is?

Edit: looks like /usr/lib/dart/bin: https://github.com/dart-lang/dart-docker/blob/main/stable/bullseye/Dockerfile#L54

[mnordine]

Yes, the following results in a ~21MB image:

FROM dart:2.17 AS build

WORKDIR /app
COPY pubspec.yaml .
RUN dart pub get

COPY . .
RUN dart pub get --offline
RUN dart compile jit-snapshot bin/server.dart

FROM scratch
COPY --from=build /runtime/ /
COPY --from=build /app/bin/server.jit app/bin/
COPY --from=build /usr/lib/dart/bin/dart /usr/bin/
EXPOSE 4002
ENTRYPOINT ["dart", "/app/bin/server.jit"]

I think this should be documented on the image page in Docker Hub.

[cpswan]

@mnordine you could propose a change to the README at https://github.com/docker-library/docs/tree/master/dart so that it gives examples for AOT and JIT