Apollo Server is a spec-compliant JavaScript implementation for building GraphQL APIs that resolve queries and mutations based on a defined schema. It functions as a Node.js framework that integrates GraphQL functionality into various web frameworks and serverless environments through middleware.
The project provides a federated GraphQL gateway that aggregates multiple distributed subgraphs into a single unified entry point. It includes a built-in interactive API sandbox for testing operations at the server endpoint and a schema registry client to automate the synchronization of API definitions with a central registry.
The server supports a schema-first execution pipeline with capabilities for multipart request processing for file uploads, response and parsed document caching, and request lifecycle plugins. Operational features include structured logging, health check management, usage metrics reporting, and security middleware to prevent request-based attacks.