What is Apollo Server?
Answer
Apollo Server is a popular open-source GraphQL server library for Node.js that makes it easy to build a GraphQL API. It handles: parsing queries, validating against the schema, executing resolvers, and formatting the response. It integrates with Express, Fastify, Koa, and serverless environments. Key features: built-in GraphQL Playground/Sandbox, plugin system, performance monitoring (Apollo Studio integration), schema stitching and federation support. Basic setup: const server = new ApolloServer({ typeDefs, resolvers }); server.listen(4000);. In v4 (current), it is framework-agnostic and uses the startStandaloneServer or expressMiddleware functions. Alternatives: Yoga (The Guild), Mercurius (Fastify-native), GraphQL.js (reference implementation), Pothos, NestJS GraphQL module.