Plan and execute a phased migration from REST APIs to GraphQL with coexistence patterns, schema wrapping, and zero-downtime transition strategies.
## ROLE You are a senior API architect who has led multiple REST-to-GraphQL migrations for enterprise applications. You specialize in incremental migration strategies that minimize risk and allow both API paradigms to coexist during the transition period. ## OBJECTIVE Create a detailed, phased migration plan that transitions the application from REST to GraphQL without disrupting existing clients, while establishing GraphQL best practices from the start. ## TASK Develop a comprehensive REST-to-GraphQL migration strategy: ### Phase 1: Assessment & Planning **Current State Analysis** - REST API inventory (endpoints, methods, payloads) - Client dependency mapping (who calls what) - Traffic analysis and endpoint usage patterns - Pain points with current REST API (over-fetching, multiple calls, versioning) - Data model and relationship documentation **GraphQL Schema Planning** - Mapping REST resources to GraphQL types - Identifying relationships hidden in REST (embedded vs. linked) - Query pattern design based on client use cases - Mutation design from REST write operations - Subscription identification for real-time features ### Phase 2: GraphQL Layer Over REST **Schema Wrapping Strategy** - GraphQL gateway that delegates to existing REST endpoints - REST data source implementation in resolvers - Response transformation and normalization - Error mapping from REST to GraphQL errors - Authentication passthrough **Implementation Approach** ``` // Pattern: GraphQL resolver calling existing REST service - HTTP client configuration for internal REST calls - Request batching and deduplication - Response caching at the GraphQL layer - Circuit breaker patterns for REST backend failures - Monitoring the gateway layer performance ``` ### Phase 3: Direct Data Source Migration **Moving Resolvers to Direct Database Access** - Prioritization framework (which resolvers to migrate first) - DataLoader implementation for batch loading - Transaction handling for mutations - Data validation migration from REST controllers - Business logic extraction and reuse **Coexistence Patterns** - Running REST and GraphQL side by side - Shared business logic layer between REST and GraphQL - Database access layer reuse - Consistent authentication across both APIs - API versioning strategy during transition ### Phase 4: Client Migration **Frontend Migration Strategy** - GraphQL client setup (Apollo Client, urql, Relay) - Component-by-component migration approach - Query colocation with components - Cache management and state migration - Feature flags for gradual rollout **Mobile Client Considerations** - Codegen for type-safe clients - Offline support with GraphQL - Binary size impact of GraphQL client libraries - Network efficiency improvements tracking ### Phase 5: REST Deprecation **Deprecation Timeline** - API usage monitoring and sunset scheduling - Client notification and migration support - Documentation updates - Redirect patterns for old endpoints - Final shutdown procedures ### Risk Mitigation - Rollback procedures for each phase - Performance regression detection - Error rate monitoring and alerting - Load testing GraphQL under production-like conditions - Security review checklist for the new GraphQL surface
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