Experimental Docker Engine

Configure the Docker engine for experimental work. Engine settings should appear in Docker Desktop as follows. Experimental changes from false to true.

{
  "builder": {
    "gc": {
      "defaultKeepStorage": "20GB",
      "enabled": true
    }
  },
  "experimental": true,
  "features": {
    "buildkit": true
  }
}

This enables the buildx Docker commands for extended build capabilities including cross-platform support. Usage below.

Usage:  docker buildx [OPTIONS] COMMAND

Extended build capabilities with BuildKit

Options:
      --builder string   Override the configured builder instance

Management Commands:
  imagetools  Commands to work on images in registry

Commands:
  bake        Build from a file
  build       Start a build
  create      Create a new builder instance
  du          Disk usage
  inspect     Inspect current builder instance
  ls          List builder instances
  prune       Remove build cache
  rm          Remove a builder instance
  stop        Stop builder instance
  use         Set the current builder instance
  version     Show buildx version information

Run 'docker buildx COMMAND --help' for more information on a command.

Alpine 32-Bit ARM

Docker’s platforms also now enable the following, covering 64-bit ARM, 32-bit ARM with Thumb (v6) and with Thumb-2.

• linux/amd64
• linux/arm64
• linux/riscv64
• linux/ppc64le
• linux/s390x
• linux/386
• linux/arm/v7
• linux/arm/v6

Launch an Alpine container for ARM v7. Remove it on exit and connect it to the terminal interactively, options --rm and -it respectively.

docker run --platform linux/arm/v7 --rm -it alpine

Asking for the process table from within the container shows QEMU running the BusyBox shell. The ARM emulator runs the shell, /usr/bin/qemu-arm. References to /bin/sh become /bin/busybox by symbolic link on BusyBox-based distributions; one binary to rule them all!—J.R.R. Tolkien, 1954–1955

/ # ps
PID   USER     TIME  COMMAND
    1 root      0:00 {sh} /usr/bin/qemu-arm /bin/sh /bin/sh
    8 root      0:00 ps

apk add build-base

/ # objdump -d /bin/busybox | head

/bin/busybox:     file format elf32-littlearm

Disassembly of section .init:

000055b0 <_init>:
    55b0:       b501            push    {r0, lr}
    55b2:       e8bd 4001       ldmia.w sp!, {r0, lr}
    55b6:       4770            bx      lr

model name      : 11th Gen Intel(R) Core(TM) i7-1165G7 @ 2.80GHz