🤖 ci: optimize CI/CD with Docker cache and remove Buildx

adr/0020-docker-build-strategy.md

@@ -31,12 +31,14 @@ This approach is simpler, more reliable, and works consistently with self-signed
 
 ## Decision
 
-**Replace Docker Buildx with traditional docker build + push** for the CI/CD pipeline.
+**Replace Docker Buildx with traditional docker build + push** for the CI/CD pipeline and implement a two-stage Docker build strategy.
 
 ### Implementation
 
+#### 1. Build Cache Strategy
+
 ```yaml
-# New approach
+# Build cache using traditional docker build
 - name: Build and push Docker cache image
   if: steps.check_cache.outputs.cache_hit == 'false'
   run: |
@@ -55,14 +57,121 @@ This approach is simpler, more reliable, and works consistently with self-signed
     echo "✅ Build cache image pushed successfully"
 ```
 
+#### 2. Production Build Strategy
+
+```yaml
+# Production build using Dockerfile.prod
+- name: Build and push Docker image
+  if: github.ref == 'refs/heads/main'
+  run: |
+    source VERSION
+    IMAGE_VERSION="$MAJOR.$MINOR.$PATCH${PRERELEASE:+-$PRERELEASE}"
+    
+    TAGS="$IMAGE_VERSION latest ${{ github.sha }}"
+    echo "Building Docker image with tags: $TAGS"
+    
+    # Use the production Dockerfile that leverages the build cache
+    docker build -t dance-lessons-coach -f Dockerfile.prod .
+    
+    for TAG in $TAGS; do
+      IMAGE_NAME="${{ env.CI_REGISTRY }}/${{ env.GITEA_ORG }}/${{ env.GITEA_REPO }}:$TAG"
+      echo "Tagging and pushing: $IMAGE_NAME"
+      docker tag dance-lessons-coach "$IMAGE_NAME"
+      docker push "$IMAGE_NAME"
+    done
+```
+
+#### 3. Dockerfile Structure
+
+**Dockerfile.build** - Build environment with all dependencies:
+```dockerfile
+FROM golang:1.26.1-alpine AS builder
+
+# Install build dependencies
+RUN apk add --no-cache git bash curl make gcc musl-dev bc grep sed jq ca-certificates
+
+# Install Go tools
+RUN go install github.com/swaggo/swag/cmd/swag@latest
+
+# Copy and verify dependencies
+COPY go.mod go.sum ./
+RUN go mod download && go mod verify
+
+WORKDIR /workspace
+```
+
+**Dockerfile.prod** - Minimal production image:
+```dockerfile
+# Use the build cache image as base
+FROM gitea.arcodange.lab/arcodange/dance-lessons-coach-build-cache:latest AS builder
+
+# Final minimal image
+FROM alpine:3.18
+
+WORKDIR /app
+
+# Install minimal dependencies
+RUN apk add --no-cache ca-certificates tzdata
+
+# Copy binary from builder
+COPY --from=builder /workspace/dance-lessons-coach /app/dance-lessons-coach
+
+# Copy configuration
+COPY config.yaml /app/config.yaml
+
+# Set permissions and entrypoint
+RUN chmod +x /app/dance-lessons-coach
+ENV TZ=UTC
+EXPOSE 8080
+ENTRYPOINT ["/app/dance-lessons-coach"]
+```
+
+**Dockerfile** - Development Dockerfile (kept for local development):
+```dockerfile
+# Multi-stage build for development
+FROM golang:1.26.1-alpine AS builder
+WORKDIR /app
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . ./
+RUN go build -o /dance-lessons-coach ./cmd/server
+
+FROM alpine:3.18
+WORKDIR /app
+RUN apk add --no-cache ca-certificates tzdata
+COPY --from=builder /dance-lessons-coach /app/dance-lessons-coach
+COPY config.yaml /app/config.yaml
+RUN chmod +x /app/dance-lessons-coach
+ENV TZ=UTC
+EXPOSE 8080
+ENTRYPOINT ["/app/dance-lessons-coach"]
+```
+
 ## Benefits
 
+### CI/CD Pipeline Benefits
+
 1. **Simplicity**: Traditional approach is easier to understand and debug
 2. **Reliability**: Consistent behavior across different environments
 3. **Certificate Handling**: Works seamlessly with self-signed certificates
 4. **Performance**: Faster execution without Buildx overhead
 5. **Compatibility**: Better compatibility with GitHub Actions environment
 
+### Two-Stage Build Benefits
+
+1. **Separation of Concerns**: Clear separation between build environment and production runtime
+2. **Optimized Production Image**: Minimal Alpine-based image with only necessary dependencies
+3. **Reusable Build Cache**: Build environment can be reused across multiple CI runs
+4. **Faster CI Execution**: Pre-built build cache reduces CI execution time
+5. **Consistent Builds**: All builds use the same build environment
+
+### Development vs Production Clarity
+
+1. **Development Dockerfile**: Full build environment for local development
+2. **Production Dockerfile**: Minimal runtime environment for deployment
+3. **Build Cache Dockerfile**: Optimized build environment for CI/CD
+4. **Clear Documentation**: Each Dockerfile has a specific purpose
+
 ## Trade-offs
 
 ### What We Lose