[StackOverflow/docker] Best practice to build flutter docker image on mac non-x86 for use on x86-64 machine

### ROOT CAUSE The issue arises because the user is attempting to build a Flutter Docker image on an ARM-based Mac (non-x86) to produce artifacts for an x86-64 machine. Flutter's default build process targets the host architecture, and cross-compilation for different architectures (like x86-64) isn't natively supported. The challenge involves ensuring the Docker image includes the necessary tools (like QEMU) for cross-compilation and properly configuring the build environment. ### CODE FIX Use a multi-architecture Docker image and configure the build to target x86-64 via QEMU emulation. Here's the solution: 1. **Dockerfile**: Use a base image with ARM support and install QEMU for cross-compilation. 2. **Build Configuration**: Set environment variables to target x86-64 and use `buildx` for multi-arch builds. ```dockerfile # Dockerfile FROM --platform=linux/arm64v8 ubuntu:20.04 # Install dependencies RUN apt-get update && apt-get install -y \ build-essential \ qemu-user-static \ git \ curl \ && rm -rf /var/lib/apt-get/lists/* # Install Flutter RUN curl -o flutter.tar.gz https://storage.googleapis.com/flutter_infra_release/flutter/a48e0478ef/flutter_linux_3.10.10.tar.gz \ && tar -xzvf flutter.tar.gz -C /opt \ && mv /opt/flutter_linux_3.10.10 /opt/flutter \ && export PATH="/opt/flutter/bin:$PATH" # Configure QEMU for cross-compilation COPY qemu-overlay/etc /etc RUN ln -s /usr/bin/qemu-x86_64-static /usr/bin/qemu-x86_64-static # Build for x86-64 CMD ["sh", "-c", "flutter build apk --target-platform=android-x64"] ``` **Steps to build:** 1. Install `docker buildx` plugin (if not enabled by default). 2. Build the image with platform targeting: ```bash docker buildx build --platform linux/amd64 -t flutter-x86 --push . ``` **Explanation:** - The `--platform` flag forces Docker to build for the specified architecture. - `qemu-user-static` enables cross-compilation by translating system calls. - Flutter's `--target-platform` flag directs the build to use the x86-64 architecture. This approach ensures the Docker image runs on ARM but produces x86-64 artifacts by leveraging QEMU for emulation.