Trivago built an internal GraphQL gateway to unify 15+ fragmented internal APIs—REST endpoints, databases, gRPC services—into a single queryable interface powering their admin tooling. Using GraphQL Mesh for schema stitching and transforms, the gateway centralizes authentication, authorization, caching, and audit logging without requiring upstream services to change. Six years in, the team shares key lessons: the gateway became a mirror revealing hidden data relationships and organizational gaps, a flat graph works better than deeply merged entities for internal use, and the lack of a schema registry from day one caused ongoing pain. The post also explores how the unified, well-typed, access-controlled graph could serve as a foundation for AI agents using protocols like MCP.
