dokku-docker-compose/docs/ARCHITECTURE.md

Dokku Docker Compose Plugin Architecture

Overview

This document describes the architecture of the Dokku Docker Compose plugin, which enables importing Docker Compose files into Dokku while maintaining compatibility with existing Dokku plugins and features.

High-Level Architecture

graph TD
    A[Docker Compose File] --> B[Parser]
    B --> C[Service Graph]
    C --> D[Transformer]
    D --> E[Dokku Resources]
    E --> F[Dokku Core]
    G[Plugins] --> F
    H[CLI] --> B
    H --> D
    H --> F

Core Components

1. Parser

• Responsibility: Parse and validate Docker Compose files
• Input: docker-compose.yml (v2/v3)
• Output: Normalized service definitions
• Features:
  • YAML parsing with schema validation
  • Environment variable interpolation
  • Extension point for custom validators

2. Service Graph

• Responsibility: Model service dependencies and relationships
• Components:
  • Dependency resolver
  • Cycle detection
  • Topological sorter
• Features:
  • Builds directed acyclic graph (DAG) of services
  • Determines execution order
  • Identifies independent services for parallel processing

3. Transformer

• Responsibility: Convert Docker Compose concepts to Dokku resources
• Components:
  • Resource mappers (networks, volumes, etc.)
  • Plugin detector
  • Environment variable processor
• Features:
  • Handles Docker-specific configurations
  • Integrates with Dokku plugins
  • Manages resource naming and references

4. Executor

• Responsibility: Coordinate the creation/update of Dokku resources
• Components:
  • Operation planner
  • Dependency manager
  • Rollback handler
• Features:
  • Transactional updates
  • Parallel execution where possible
  • Automatic rollback on failure

Data Flow

1. Initialization:

   • Load and parse docker-compose.yml
   • Resolve environment variables
   • Validate against schema

2. Analysis:

   • Build service dependency graph
   • Detect plugin integrations
   • Plan operations

3. Execution:

   • Create/update resources in dependency order
   • Handle plugin integrations
   • Configure networking and storage

4. Verification:

   • Run health checks
   • Verify service availability
   • Perform post-deployment tasks

Key Design Decisions

1. Plugin Integration

• Approach: Use Dokku's plugin system for service management
• Rationale: Leverage existing, well-tested implementations
• Implementation:
  • Detect compatible plugins based on image names
  • Map Docker Compose configurations to plugin commands
  • Fall back to container-based deployment when no plugin is available

2. State Management

• Approach: Store minimal state in Dokku's configuration
• Rationale: Ensure consistency and enable recovery
• Implementation:
  • Store original compose file checksum
  • Track resource mappings
  • Maintain version history

3. Error Handling

• Approach: Fail fast with clear error messages
• Rationale: Prevent partial or inconsistent states
• Implementation:
  • Input validation
  • Pre-flight checks
  • Transactional updates with rollback

Integration Points

Dokku Core

• App management
• Network configuration
• Volume management
• Process management

External Systems

• Docker Registry (for image pulls)
• Docker Daemon (for container operations)
• System Package Manager (for plugin installation)

Security Considerations

1. Input Validation:

   • Sanitize all inputs
   • Validate against schema
   • Restrict file system access

2. Secret Management:

   • Handle environment variables securely
   • Support Dokku's secret management
   • Avoid logging sensitive data

3. Access Control:

   • Respect file permissions
   • Run with least privilege
   • Validate user permissions

Performance Considerations

1. Parallel Processing:

   • Process independent services concurrently
   • Limit concurrency to prevent resource exhaustion

2. Caching:

   • Cache parsed compose files
   • Store intermediate build artifacts

3. Optimizations:

   • Lazy loading of resources
   • Incremental updates
   • Batch operations where possible

Monitoring and Observability

1. Logging:

   • Structured logging
   • Different log levels
   • Operation context

2. Metrics:

   • Operation duration
   • Resource usage
   • Success/failure rates

3. Tracing:

   • Request tracing
   • Dependency tracking
   • Performance analysis

Future Extensions

1. Plugin System:

   • Custom transformers
   • Additional validators
   • Post-processing hooks

2. Export Functionality:

   • Generate compose files from existing Dokku apps
   • Support for different output formats

3. Advanced Features:

   • Blue/green deployments
   • Canary releases
   • A/B testing support