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ADR-001: Adopt Microservices Architecture

Status​

Accepted - 2024-01-15

Context​

Our platform has grown significantly, and we're experiencing challenges with our current monolithic architecture:

  • Deployment Complexity: Changes to any part of the system require full application deployment
  • Scaling Limitations: Cannot scale individual components independently based on demand
  • Technology Constraints: Entire application is tied to a single technology stack
  • Team Dependencies: Multiple teams working on the same codebase creates coordination overhead
  • Fault Isolation: Issues in one component can affect the entire system

We need an architecture that supports:

  • Independent service deployment and scaling
  • Technology diversity for optimal tool selection
  • Team autonomy and parallel development
  • Better fault isolation and resilience

Decision​

We will adopt a microservices architecture with the following principles:

Service Boundaries​

  • Services are organized around business capabilities
  • Each service owns its data and business logic
  • Services communicate through well-defined APIs
  • Database-per-service pattern to ensure data ownership

Communication Patterns​

  • Synchronous: REST APIs for real-time request/response
  • Asynchronous: Event-driven messaging for eventual consistency
  • Service Discovery: Centralized service registry for dynamic discovery

Technology Stack​

  • API Gateway: Single entry point for client requests
  • Container Orchestration: Kubernetes for deployment and scaling
  • Service Mesh: Istio for service-to-service communication
  • Monitoring: Distributed tracing and centralized logging

Deployment Strategy​

  • CI/CD Pipelines: Independent deployment pipelines per service
  • Blue-Green Deployment: Zero-downtime deployments
  • Canary Releases: Gradual rollout of new versions

Consequences​

Positive​

  • Independent Scaling: Services can be scaled based on individual demand
  • Technology Flexibility: Teams can choose optimal technologies for their services
  • Fault Isolation: Failures in one service don't bring down the entire system
  • Team Autonomy: Teams can develop, test, and deploy independently
  • Faster Development: Parallel development reduces time to market

Negative​

  • Increased Complexity: Distributed systems are inherently more complex
  • Network Latency: Inter-service communication introduces network overhead
  • Data Consistency: Managing consistency across services requires careful design
  • Operational Overhead: More services mean more monitoring and maintenance
  • Testing Complexity: Integration testing becomes more challenging

Mitigation Strategies​

  • Service Mesh: Implement Istio for traffic management and observability
  • Circuit Breakers: Prevent cascade failures with circuit breaker patterns
  • Monitoring: Comprehensive observability with distributed tracing
  • Documentation: Maintain clear API documentation and service contracts
  • Testing: Implement contract testing and service virtualization

Implementation Plan​

Phase 1: Foundation (Months 1-2)​

  • Set up container orchestration platform (Kubernetes)
  • Implement API Gateway and service discovery
  • Establish CI/CD pipelines and deployment practices

Phase 2: Service Extraction (Months 3-6)​

  • Identify and extract first microservices from monolith
  • Implement event-driven messaging infrastructure
  • Establish monitoring and observability practices

Phase 3: Full Migration (Months 6-12)​

  • Complete migration of remaining monolith components
  • Optimize service boundaries based on operational experience
  • Implement advanced patterns (CQRS, Event Sourcing) where appropriate

References​

Related ADRs:

  • ADR-002: Event-Driven Architecture (Coming Soon)
  • ADR-003: Database per Service (Coming Soon)

Last Updated: 2024-01-15
Next Review: 2024-07-15