KrakenD

KrakenD is an ultra-high-performance open-source API Gateway written in Go, designed to aggregate, transform, and filter multiple backend microservices into clean frontend APIs. Created by Daniel Castejon and the KrakenD team, it processes requests with sub-millisecond overhead by running entirely in memory without databases or external state stores. KrakenD serves as an API Gateway, Backend-for-Frontend (BFF), and API Aggregator, capable of combining data from multiple backend endpoints into a single response through its declarative pipeline architecture. Key features include: request/response aggregation from multiple endpoints, data filtering and field selection (allowing clients to request only needed fields), protocol conversion (REST to gRPC, AMQP, Lambda, GraphQL, MQTT), payload transformation (mapping, renaming, deleting, and combining fields), circuit breaker pattern, rate limiting (per endpoint and per consumer), OAuth2 and JWT authentication, CORS handling, and response caching with Redis or memory backends. The declarative configuration (krakend.json) defines endpoints, backend connections, and middleware pipelines. KrakenD Enterprise adds a GUI designer (KrakenDesigner), Prometheus and OpenTelemetry observability, CI/CD plugins, and 24/7 support. As of 2026, the Community Edition has over 7,400 stars, licensed under Apache 2.0, with clients including Tesla, Telefonica, Sony, and BBVA.