Add Docker Compose scanner with multi-container support

[rubys]

Summary

This PR adds comprehensive Docker Compose support to flyctl, enabling deployment of existing Docker Compose applications to Fly.io with minimal changes by translating compose configurations to multi-container machine specs.

Key Features

🐳 Docker Compose Scanner

• Detects and parses docker-compose.yml files automatically during fly launch
• Maps Docker Compose services to Fly.io multi-container machine configuration
• Supports compose versions 3.x with comprehensive service configuration

🔧 Service Configuration Support

• Ports: Maps exposed ports and port mappings
• Environment Variables: Handles both map and array formats
• Volumes: Converts bind mounts to container file configurations
• Health Checks: Translates Docker Compose health checks to Fly.io format
• Dependencies: Preserves service dependencies with condition mapping
• Restart Policies: Maps Docker restart policies to Fly.io equivalents

🗄️ Database Integration

• Intelligent Detection: Automatically detects PostgreSQL, MySQL, and Redis services
• Managed Service Recommendations: Proposes Fly managed databases during launch
• Credential Extraction: Extracts database credentials as secrets when using external containers
• Flexible Deployment: Choose between managed services or container-based databases
• Single-Container Optimization: When database services are replaced with managed services and only one container remains, automatically switches to single-container deployment mode

🏗️ Build Support

• Single Build Service: Supports one service with build section for traditional workflows
• Multiple Identical Builds: Supports multiple services with identical build definitions
• Build Validation: Ensures all build configurations are truly identical (context, dockerfile, args, target)
• Image Distribution: All containers with identical builds receive the same built image
• Mixed Deployments: Combines built and pre-built images in the same application

🔐 Security & Secrets

• Docker Compose Secrets: Processes secrets section and file-based secrets
• Database Credentials: Automatically extracts and secures database connection details
• Environment Isolation: Separates sensitive configuration from regular environment variables

🌐 Service Discovery

• Internal Networking: Containers can communicate using service names
• Automatic /etc/hosts: Generates service discovery for multi-container deployments
• Localhost Communication: Services accessible via localhost and respective ports

⚡ Intelligent Deployment Optimization

• Processes Mode: Automatically converts services with identical builds and environments to processes-based deployment
• Multi-Container Mode: Used when services have different configurations or volumes
• Single-Container Mode: Selected when only one service remains after database filtering
• Volume Awareness: Preserves multi-container mode when services use volumes

Implementation Highlights

Multiple Build Services Support

Docker Compose files with multiple services sharing identical build definitions are fully supported:

version: '3.8'
services:
  web:
    build: .
    ports: ["3000:3000"]
  
  worker:
    build: .  # Same build definition as web
    environment: [WORKER=true]
  
  api:
    build: .  # Same build definition as web  
    ports: ["4000:4000"]

All three services receive the same built image, with web as the primary container in fly.toml.

Processes-Based Deployment

When services have identical builds and environments (and no volumes), they're automatically converted to processes:

version: '3.8'
services:
  web:
    build: .
    environment: [NODE_ENV=production]
    # Uses CMD from Dockerfile
  
  worker:
    build: .
    environment: [NODE_ENV=production]
    command: ["npm", "run", "worker"]
  
  scheduler:
    build: .
    environment: [NODE_ENV=production]
    command: ["npm", "run", "scheduler"]

Results in a processes-based fly.toml with one build and multiple processes sharing the same image.

Deployment Mode Selection

• Processes Mode: Services with identical builds, environments, and no volumes
• Multi-Container Mode: Services with different configurations, images, or volumes
• Single-Container Mode: Only one service remains after database filtering
• Automatic Detection: No manual configuration needed, optimal mode chosen automatically

Architecture

• Scanner Integration: Plugs into existing flyctl scanner framework
• Machine Configuration: Generates proper fly.machine.json for multi-container deployments
• Launch Callback: Post-processing logic filters services based on user database choices
• Backward Compatibility: Maintains compatibility with existing single-container workflows

File Changes

Core Implementation

• scanner/docker_compose.go - Main Docker Compose parsing and configuration logic
• scanner/scanner.go - Enhanced SourceInfo struct with container support
• internal/command/launch/launch_frameworks.go - Multi-container launch integration

Configuration & Deploy

• internal/appconfig/config.go - Extended Config struct for multi-container builds
• internal/command/deploy/machines_launchinput.go - Deploy logic for multiple build containers

Testing

• scanner/docker_compose_test.go - Comprehensive test coverage including deployment mode selection

Test Coverage

✅ Basic Docker Compose Detection
✅ Service Configuration Mapping
✅ Database Service Detection
✅ Build Context Handling
✅ Health Check Translation
✅ Volume and Bind Mount Processing
✅ Environment Variable Handling
✅ Multiple Identical Build Sections
✅ Different Build Section Validation
✅ Secrets and Credential Extraction
✅ Single-Container Mode Optimization
✅ Processes-Based Deployment
✅ Volume-Aware Mode Selection

Usage

Simply run fly launch in a directory containing a docker-compose.yml file:

fly launch

The scanner will:

1. Detect the Docker Compose configuration
2. Analyze services and dependencies
3. Recommend managed databases for detected database services
4. Generate appropriate fly.toml and fly.machine.json configurations
5. Support deployment with multiple containers receiving the same built image
6. Automatically optimize deployment mode based on service characteristics

Backward Compatibility

• Existing single-container Docker applications continue to work unchanged
• All previous flyctl functionality remains intact
• Multi-container support is additive, not breaking

🤖 Generated with Claude Code