REL03-BP03: Provide service contracts per API

Overview

Establish clear, well-defined service contracts for each API to ensure reliable communication between services and clients. Service contracts define the interface, data formats, error handling, versioning strategy, and behavioral expectations, enabling loose coupling, independent evolution, and reliable integration patterns across distributed systems.

Implementation Steps

1. Define Comprehensive API Specifications

Create detailed OpenAPI/Swagger specifications for all service endpoints
Define request and response schemas with validation rules
Specify error codes, messages, and handling patterns
Document authentication and authorization requirements

2. Implement Contract-First Development

Design API contracts before implementation begins
Use contract specifications to generate client SDKs and server stubs
Establish contract validation in CI/CD pipelines
Implement contract testing to ensure compliance

3. Establish API Versioning Strategy

Implement semantic versioning for API contracts
Design backward-compatible changes and deprecation policies
Provide multiple API versions simultaneously during transitions
Establish clear migration paths for breaking changes

4. Implement Contract Validation and Testing

Deploy contract testing frameworks for producer and consumer validation
Implement schema validation for all API requests and responses
Create automated tests that verify contract compliance
Establish contract regression testing in deployment pipelines

5. Design Error Handling and Resilience Patterns

Define standardized error response formats across all APIs
Implement circuit breaker patterns for service dependencies
Design retry policies and timeout configurations
Establish graceful degradation strategies for service failures

6. Establish Contract Governance and Evolution

Create processes for contract change management and approval
Implement contract versioning and lifecycle management
Establish deprecation policies and migration support
Maintain contract documentation and change logs
Implementation Examples

Example 1: API Contract Management and Validation System

Example 2: API Contract Testing and Validation Script

AWS Services Used

Amazon API Gateway: RESTful API management with built-in contract validation and documentation
AWS Lambda: Serverless functions for implementing API endpoints with contract compliance
Amazon S3: Storage for API specifications, generated SDKs, and contract documentation
Amazon DynamoDB: Storage for contract metadata, versioning information, and validation results
Amazon EventBridge: Event-driven notifications for contract changes and validation results
AWS CodePipeline: CI/CD pipelines with integrated contract testing and validation
AWS CodeBuild: Build service for automated contract testing and SDK generation
Amazon CloudWatch: Monitoring and logging for API contract compliance and performance
AWS X-Ray: Distributed tracing for API request/response validation and debugging
Amazon SNS: Notifications for contract validation failures and breaking changes
AWS Systems Manager: Parameter store for API configuration and contract metadata
AWS Secrets Manager: Secure storage of API keys and authentication credentials
Amazon CloudFront: CDN for distributing API documentation and SDK downloads
AWS AppSync: GraphQL APIs with built-in schema validation and contract enforcement
Amazon Cognito: Authentication and authorization for API access control
AWS Step Functions: Workflow orchestration for complex contract validation processes

Benefits

Reliable Integration: Clear contracts ensure consistent communication between services and clients
Independent Evolution: Services can evolve independently while maintaining contract compatibility
Automated Validation: Contract testing prevents breaking changes from reaching production
Improved Documentation: Living documentation that stays synchronized with implementation
Faster Development: Generated SDKs and clear contracts accelerate client development
Better Testing: Contract-based testing ensures comprehensive API coverage
Version Management: Structured approach to API versioning and backward compatibility
Reduced Integration Issues: Early detection of contract violations prevents runtime failures
Enhanced Collaboration: Clear contracts improve communication between teams
Quality Assurance: Automated contract validation ensures API quality and consistency