Running Crystal-lang on aarch64 Linux with Docker

README.md

Running Crystal-lang on aarch64 Linux with Docker

Motivation: Oracle Cloud offers an "always-free" tier with Ampere CPU (aarch64 architecture). You can run the latest Ubuntu on it, but unfortunately, Crystal-lang is not available on aarch64.

To run Crystal-lang, I used docker and qemu. NOTE: it is very slow!

First, install docker, docker-compose, and qemu. For qemu, I used the following command to install everything:

sudo apt-get install \
  qemu \
  qemu-user-static \
  qemu-user \
  qemu-system-x86 \
  qemu-system-arm \
  qemu-system-mips \
  qemu-system-ppc \
  qemu-system-sparc \
  qemu-system-m68k \
  qemu-system-microblaze \
  qemu-system-microblazeel \
  qemu-system-sh4 \
  qemu-system-sh4eb \
  qemu-system-s390x \
  qemu-system-riscv64 \
  qemu-system-riscv32

Then, test that docker can run foreign platform images:

uname -m
docker run --rm -ti --platform linux/amd64 alpine:latest uname -m

Now it's time to build a Docker image and run it. Everything has been wrapped in the docker-compose.yml file. You should use the docker compose or docker-compose command, depending on your environment.

Thanks to build args, it's possible to solve user permission issues. Docker image runs as a host user. To build the image, use the following command:

docker compose build \
  --build-arg DOCKER_USER=$(whoami) \
  --build-arg DOCKER_USER_ID=$(id --user) \
  --build-arg DOCKER_GROUP_ID=$(id --group)

And run it:

docker compose run -i crystal crystal ./hello-world.cr

Result:

Hello from x86_64

Finally, note that Crystal is available in both Alpine and Ubuntu flavors. You can check the Dockerfile for the FROM instruction.

docker-compose.yml

version: '3.8'

services:
  crystal:
    # Build it this way:
    # ```
    # docker compose build --build-arg USER=$(whoami) --build-arg USER_ID=$(id --user) --build-arg GROUP_ID=$(id --group)
    # ```
    #
    # and run
    # ```
    # docker compose run -i crystal bash
    # ```
    build:
      context: .
      args:
        USER: ${USER:-app}
        USER_ID: ${USER_ID:-1000}
        GROUP_ID: ${USER_ID:-1000}
    platform: linux/amd64
    # command: ["echo", "Hello, world!"]
    # environment:
    #   USER: $(whoami)
    #   USER_ID: $(id --user)
    #   GROUP_ID: $(id --group)
    volumes:
      - .:/app/

Dockerfile

FROM crystallang/crystal:1.8
# FROM crystallang/crystal:1.8-alpine

ARG USER=user
ARG USER_ID=1000
ARG GROUP_ID=1000

RUN sh <<'EOF'
    if [ "$(awk -F= '/^ID=/{print $2}' /etc/os-release)" = "alpine" ]; then
      apk add bash curl
      addgroup -g $GROUP_ID $USER
      adduser -u $USER_ID -G $USER -s /bin/bash -D $USER
    else
      apt-get -q update
      apt-get -yqq install bash curl
      groupadd -g $GROUP_ID $USER
      useradd -u $USER_ID -g $GROUP_ID -ms /bin/bash $USER
    fi
EOF

USER $USER:$USER

WORKDIR /app

SHELL ["/bin/bash", "-c"]

hello-world.cr

arch = %x(uname -m).chomp

puts "Hello from #{arch}"