Multi-Architecture Builds

# Build architecture-specific images with separate tags
docker build -t username/myapp:amd64 --platform linux/amd64 .
docker build -t username/myapp:arm64 --platform linux/arm64 .

# Create a manifest list that references both architecture variants
docker manifest create username/myapp:latest \
  username/myapp:amd64 \
  username/myapp:arm64

# Push the manifest list to the registry
docker manifest push username/myapp:latest

# View manifest details including all architecture variants
docker manifest inspect username/myapp:latest

# Output shows details like:
# - Supported architectures and OS
# - Digest (content hash) for each variant
# - Size of each variant
# - Platform-specific annotations

name: Build Multi-Arch Image

on:
  push:
    branches: [ main ]
  # Optionally trigger on tags for releases
  tags:
    - 'v*'

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v3
        
      - name: Set up QEMU
        uses: docker/setup-qemu-action@v2
        # This installs QEMU static binaries for multi-architecture builds
        
      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v2
        # Creates a new builder instance with multi-architecture support
        
      - name: Login to DockerHub
        uses: docker/login-action@v2
        with:
          username: ${{ secrets.DOCKERHUB_USERNAME }}
          password: ${{ secrets.DOCKERHUB_TOKEN }}
          # Authenticate to enable pushing to Docker Hub
          
      - name: Extract metadata for Docker
        id: meta
        uses: docker/metadata-action@v4
        with:
          images: username/myapp
          # Automatically generate tags based on branches and version tags
          tags: |
            type=semver,pattern={{version}}
            type=semver,pattern={{major}}.{{minor}}
            type=ref,event=branch
          
      - name: Build and push
        uses: docker/build-push-action@v4
        with:
          context: .
          platforms: linux/amd64,linux/arm64  # Specify target architectures
          push: true
          tags: ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          cache-from: type=registry,ref=username/myapp:buildcache
          cache-to: type=registry,ref=username/myapp:buildcache,mode=max
          # Caching improves build performance for frequent builds

build-multi-arch:
  image: docker:20.10.16
  services:
    - docker:20.10.16-dind  # Docker-in-Docker service
  variables:
    DOCKER_BUILDKIT: 1
    DOCKER_TLS_CERTDIR: "/certs"  # Enable TLS for Docker-in-Docker
    BUILDX_VERSION: "0.9.1"       # Specify buildx version
  before_script:
    # Login to registry
    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
    
    # Setup buildx with multi-architecture support
    - mkdir -p ~/.docker/cli-plugins
    - wget -O ~/.docker/cli-plugins/docker-buildx https://github.com/docker/buildx/releases/download/v${BUILDX_VERSION}/buildx-v${BUILDX_VERSION}.linux-amd64
    - chmod +x ~/.docker/cli-plugins/docker-buildx
    - docker context create builder-context
    - docker buildx create --name mybuilder --use builder-context
    - docker buildx inspect --bootstrap
    
    # Set tag based on CI_COMMIT_REF_NAME
    - |
      if [[ $CI_COMMIT_TAG ]]; then
        export IMAGE_TAG=$CI_COMMIT_TAG
      else
        export IMAGE_TAG=$CI_COMMIT_REF_NAME
      fi
  script:
    - docker buildx build --platform linux/amd64,linux/arm64 
      -t $CI_REGISTRY_IMAGE:$IMAGE_TAG 
      -t $CI_REGISTRY_IMAGE:latest 
      --build-arg BUILD_DATE=$(date -u +'%Y-%m-%dT%H:%M:%SZ') 
      --build-arg VCS_REF=$CI_COMMIT_SHA 
      --push .
  # Run on both branch pushes and tags
  rules:
    - if: $CI_COMMIT_BRANCH || $CI_COMMIT_TAG

FROM --platform=$TARGETPLATFORM python:3.10-slim

# Install architecture-specific optimizations
RUN case "$(uname -m)" in \
      "x86_64") \
        apt-get update && apt-get install -y --no-install-recommends \
        libjemalloc2 && \
        # Use jemalloc memory allocator for better performance on x86_64
        echo "/usr/lib/x86_64-linux-gnu/libjemalloc.so.2" > /etc/ld.so.preload \
        ;; \
      "aarch64") \
        apt-get update && apt-get install -y --no-install-recommends \
        # libatomic1 is needed for some operations on ARM64
        libatomic1 \
        # ARM-specific optimizations
        && apt-get install -y --no-install-recommends libneon27 \
        ;; \
      "armv7l") \
        # 32-bit ARM specific packages
        apt-get update && apt-get install -y --no-install-recommends \
        libatomic1 libarmmem-${TARGETARCH} \
        ;; \
      *) \
        echo "Architecture $(uname -m) not explicitly optimized, using defaults" \
        ;; \
    esac

# Continue with common setup
COPY requirements.txt .
RUN pip install -r requirements.txt

# docker-compose.override.yml
services:
  app:
    build:
      args:
        - TARGETARCH=${TARGETARCH:-amd64}
        # Default to amd64 if not specified
        
        # Additional platform-specific build args
        - EXTRA_FEATURES=${EXTRA_FEATURES:-}
        # Can be set differently per architecture in CI/CD
    
    # Conditionally apply platform-specific volumes or configurations
    volumes:
      - ${PLATFORM_SPECIFIC_VOLUME:-/tmp}:/opt/platform-specific

# Build script to generate platform-specific configurations
#!/bin/bash
TARGETARCH=${TARGETARCH:-$(uname -m)}

case "$TARGETARCH" in
  "x86_64"|"amd64")
    # Generate x86-specific configuration
    echo "Generating x86_64 optimized configuration"
    cat base-config.json | jq '.optimizations.simd = true' > config.json
    ;;
  "aarch64"|"arm64")
    # Generate ARM64-specific configuration
    echo "Generating ARM64 optimized configuration"
    cat base-config.json | jq '.optimizations.neon = true' > config.json
    ;;
esac

# Run platform-specific build steps
docker-compose build