[SOLVED] How to build a Docker container that starts a .jar and runs on a RaspberryPi 4B?

Issue

I am working on a little application that I want to run in a docker container on a Raspberry Pi (Model 4B, 32Bit, 4GB RAM). I am learning Docker currently, so far I have only built and run stuff on my dev machine ( a mac). The container setup and jar work without problems on that machine.

This is my very basic Dockerfile:

FROM java:8
WORKDIR /
ADD my_jar.jar my_jar.jar
EXPOSE 8080
CMD java -jar my_jar.jar

As you can see there is not much going on. I would like to just be able to Docker build . -t myDockerImage on the pi and then run my container. Building succeeds, according to the output, but running fails with an error:

WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm/v7) and no specific platform was requested
standard_init_linux.go:219: exec user process caused: exec format error

I did some research, and all I could find was the suggestion to use OpenJDK. Did that, but can't build, it says:

no matching manifest for linux/arm/v7 in the manifest list entries

I looked around on Docker Hub, but it doesn't seem like there is an image for java that fits this architecture. Or maybe I don't know what to look for...?

So how do I get java in a docker container onty this machine (preferrable in a fairly easy, convenient way, but if that doesn't exist, I am happy to do it the hard way, what ever that might entail)?

Btw: This is what lshw states about the RPi:

raspberrypi
    description: ARMv7 Processor rev 3 (v7l)
    product: Raspberry Pi 4 Model B Rev 1.1
    serial: 10000000b3320840
    width: 32 bits
    capabilities: smp

Solution

The problem is that the JRE still depends on the operating system and that depends on the platform architecture. The standard docker image for Java will most likely use a amd64/x64 based Linux OS with the appropriate JDK installed.

Raspberry PI, however, uses the ARM architecture, hence the output ARMv7 Processor rev 3 (v7l).

So you need an ARM-compatible image such as one of those: https://hub.docker.com/r/arm32v7/adoptopenjdk

I'm not sure how compatible ARM v7 and v8 are so I'd suggest you stick to the v7 images :)

Answered By - Thomas