Hi there! I’m playing around with Kotlin Native, o...

# kotlin-native

[Marc Reichelt]

Hi there! I’m playing around with Kotlin Native, out of curiosity how small we can make Docker images with a single Kotlin binary. So far, I’m down to 64.6MB with an ubuntu base image:

FROM ubuntu
COPY hello_world_linux64 /hello_world
ENTRYPOINT ["/hello_world"]

But 64.2MB of those is Ubuntu itself. Is there an option for the kotlinc-native compiler to statically link all libraries? Because if I build an image from scratch, like this:

FROM scratch
COPY hello_world_linux64 /hello_world
ENTRYPOINT ["/hello_world"]

this will print this error at runtime:

standard_init_linux.go:211: exec user process caused "no such file or directory"

And by the way: merry christmas / happy holidays to everyone 😉 🎄🎁

[Dominaezzz]

At that point you'd have to bundle up the entire OS in the binary, which doesn't give you anything.

[napperley]

The biggest issue with Kotlin Native in Docker is that Kotlin Native doesn't support Musl C, therefore Alpine Linux (significantly smaller than Ubuntu) can't be used.

[napperley]

Mark - Would be interested to know how you created the Docker image. It is much smaller than the Debian one used in the weather_function sample ( https://github.com/JetBrains/kotlin-native/tree/master/samples/weather_function ).

[Marc Reichelt]

@Dominaezzz yep, it would require all the needed native code from the OS, that’s exactly what I wanted here. But the binary doesn’t use everything from the OS, and I assume it doesn’t really need everything from the linked libraries as well. I only wondered if there is an option to create a single, self-contained binary. It seems Go is able to do that - I wonder if there’s an option for kotlinc-native as well.

[Marc Reichelt]

@napperley I’m actually writing a blog post at the moment that describes exactly how I did that. 😊
As for the weather_function sample, I would think that that gets larger to due more required dependencies. I haven’t looked into it more to confirm.

[Dominaezzz]

You can make kotlinc-native statically link stuff in by using -include-binary to include static libraries. When included this way, they automatically link all symbols when building the final binary. So that's an option on Linux.

[Marc Reichelt]

Oh, that’s great! I will include you in my blog post and try this out at a later time 😊

[Marc Reichelt]

@napperley if you’re interested, I just published the blog post: https://dev.to/mreichelt/christmas-hacking-squeezing-kotlin-native-into-docker-6ao

[napperley]

The`-include-binary` flag only works for klibs unless that has changed recently.

[Dominaezzz]

Yeah, isn't that all you need it for?