distribution: Docker armhf unable to run arm64v8 containers

I reported this on the forums some years ago: https://forums.docker.com/t/unable-to-run-aarch64-containers-from-armv7-docker/67187

The problem is still there, but it’s easier to reproduce now that the Raspberry Pi Foundation provides an aarch64 kernel. To repro on Raspbian Buster:

1. Install Docker CE.

2. Run sudo rpi-update to download the latest 64-bit kernel.

3. Edit /boot/config.txt add the line arm_64bit=1, ideally under the [pi4] section if this is being tested on a Pi 4.

4. Reboot, and confirm uname -m shows you’re now running an aarch64 kernel.

pi@raspberrypi:~ $ docker run -it arm64v8/debian
pi@raspberrypi:~ $ echo $?
159

LXC, systemd-nspawn, or plain chroot do not have this problem. They are able to seamlessly jump from a 32-bit userland to a 64-bit container/chroot.

If there is a fundamental reason that this cannot work with Docker’s design, it should be documented and the command should provide a more informative message than null output with return code 159.

64-bit Docker containers on Raspberry Pi have a number of use-cases. At this time it seems that it’s only practical to run these on non-Raspbian distros that possess a native 64-bit userland.