Passing customizable options to a GraalVM image execution in a distroless environment

For context, I’m building a java application compiled to GraalVM native image running on a distroless docker image in Kubernetes.

I’ve been trying to do something rather simple and hit a wall: I’d like to set custom heap size limits per environment via -XmxNNN. To do that, the options with which I’d like to run the application would be held in an environment variable. The problem arises due to the usage of a distroless image – which doesn’t have bash and so ENTRYPOINT /application $OPTIONS doesn’t work.

Is there an environment variable GraalVM supports on its own, or any other way of setting this?

I dont want to:

• hardcode the values in the Docker image
• hardcode the values by predefining them during native-image build

Answer

You could use busybox to get a shell inside a distroless container:

FROM gcr.io/distroless/base

...

COPY --from=amd64/busybox:1.31.1 /bin/busybox /busybox/busybox
RUN ["/busybox/busybox", "--install", "/bin"]

CMD ["/bin/sh", "-c", "java -version"]

You can find an example to this kind of Dockerfile here.

But I don’t think this busybox shell is necessary needed.

Altough ENTRYPOINT /application $OPTIONS does not work, this will work ENTRYPOINT ["myapp", "arguments"]

Note that distroless images by default do not contain a shell. That means the Dockerfile ENTRYPOINT command, when defined, must be specified in vector form, to avoid the container runtime prefixing with a shell.

source: github