Architecture & Design Patterns

Anti-Corruption Layer Pattern

Problem: New systems must integrate with legacy systems that use outdated models or technologies.

Solution: Implement a façade or adapter layer between a modern application and a legacy system to prevent legacy constraints from affecting new design.

When to Use:

• Migrating from legacy systems incrementally
• Integrating with third-party systems with different domain models
• Protecting modern architectures from legacy constraints

Implementation Considerations:

• Create translation layer between domain models
• Map between legacy and modern data structures
• Isolate legacy system interfaces behind abstractions
• Consider performance impact of translation
• Plan for eventual removal if migration is complete

Backends for Frontends (BFF) Pattern

Problem: A single backend may not optimally serve different client types.

Solution: Create separate backend services to serve specific frontend applications or interfaces.

When to Use:

• Different client types (web, mobile, IoT) have different needs
• Optimizing payload size and shape per client
• Reducing coupling between frontend and shared backend

Implementation Considerations:

• Create one BFF per user experience or client type
• Tailor API contracts to frontend needs
• Avoid duplicating business logic across BFFs
• Share common services between BFFs
• Manage increased number of services

Gateway Aggregation Pattern

Problem: Clients need data from multiple backend services.

Solution: Use a gateway to aggregate multiple individual requests into a single request.

When to Use:

• Reducing chattiness between clients and backends
• Combining data from multiple sources for a single view
• Reducing latency by parallelizing backend calls

Implementation Considerations:

• API gateway aggregates responses from multiple services
• Execute backend calls in parallel where possible
• Handle partial failures appropriately
• Consider caching of aggregated responses
• Avoid creating a monolithic gateway

Gateway Offloading Pattern

Problem: Shared functionality is duplicated across multiple services.

Solution: Offload shared or specialized service functionality to a gateway proxy.

When to Use:

• Centralizing cross-cutting concerns (SSL, authentication, logging)
• Simplifying service implementation
• Standardizing shared functionality

Implementation Considerations:

• Offload SSL termination to gateway
• Implement authentication and authorization at gateway
• Handle rate limiting and throttling
• Provide request/response logging
• Avoid making gateway a bottleneck

Gateway Routing Pattern

Problem: Clients need to access multiple services through a single endpoint.

Solution: Route requests to multiple services using a single endpoint.

When to Use:

• Providing a single entry point for multiple services
• Abstracting backend service topology from clients
• Enabling service versioning and migration strategies

Implementation Considerations:

• Route based on URL path, headers, or query parameters
• Support URL rewriting and transformation
• Enable A/B testing and canary deployments
• Implement health checks for backend services
• Monitor routing performance

Sidecar Pattern

Problem: Applications need auxiliary functionality without coupling.

Solution: Deploy components of an application into a separate process or container to provide isolation and encapsulation.

When to Use:

• Adding functionality to applications without modifying them
• Implementing cross-cutting concerns (logging, monitoring, security)
• Supporting heterogeneous environments

Implementation Considerations:

• Deploy sidecar alongside main application
• Share lifecycle, resources, and network with main application
• Use for proxying, logging, configuration, or monitoring
• Consider resource overhead of additional containers
• Standardize sidecar implementations across services

Strangler Fig Pattern

Problem: Legacy systems are risky to replace all at once.

Solution: Incrementally migrate a legacy system by gradually replacing specific pieces of functionality with new applications and services.

When to Use:

• Modernizing legacy applications
• Reducing risk of big-bang migrations
• Enabling incremental business value delivery

Implementation Considerations:

• Identify functionality to migrate incrementally
• Use facade or proxy to route between old and new
• Migrate less risky components first
• Run old and new systems in parallel initially
• Plan for eventual decommissioning of legacy system