Apollo Server 4.x Guide

Apollo Server is an open-source GraphQL server that works with any GraphQL schema. Version 4.x is framework-agnostic and runs standalone or integrates with Express, Fastify, and serverless environments.

Quick Start

Step 1: Install

npm install @apollo/server graphql

For Express integration:

npm install @apollo/server express graphql cors

Step 2: Define Schema

const typeDefs = `#graphql
  type Book {
    title: String
    author: String
  }

  type Query {
    books: [Book]
  }
`;

Step 3: Write Resolvers

const resolvers = {
  Query: {
    books: () => [
      { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald' },
      { title: '1984', author: 'George Orwell' },
    ],
  },
};

Step 4: Start Server

Standalone (Recommended for getting started):

import { ApolloServer } from '@apollo/server';
import { startStandaloneServer } from '@apollo/server/standalone';

const server = new ApolloServer({ typeDefs, resolvers });

const { url } = await startStandaloneServer(server, {
  listen: { port: 4000 },
});

console.log(`Server ready at ${url}`);

Express v4:

import { ApolloServer } from '@apollo/server';
import { expressMiddleware } from '@apollo/server/express4';
import { ApolloServerPluginDrainHttpServer } from '@apollo/server/plugin/drainHttpServer';
import express from 'express';
import http from 'http';
import cors from 'cors';

const app = express();
const httpServer = http.createServer(app);

const server = new ApolloServer({
  typeDefs,
  resolvers,
  plugins: [ApolloServerPluginDrainHttpServer({ httpServer })],
});

await server.start();

app.use(
  '/graphql',
  cors(),
  express.json(),
  expressMiddleware(server, {
    context: async ({ req }) => ({ token: req.headers.authorization }),
  }),
);

await new Promise<void>((resolve) => httpServer.listen({ port: 4000 }, resolve));
console.log('Server ready at http://localhost:4000/graphql');

Schema Definition

Scalar Types

• Int - 32-bit integer
• Float - Double-precision floating-point
• String - UTF-8 string
• Boolean - true/false
• ID - Unique identifier (serialized as String)

Type Definitions

type User {
  id: ID!
  name: String!
  email: String
  posts: [Post!]!
}

type Post {
  id: ID!
  title: String!
  content: String
  author: User!
}

input CreatePostInput {
  title: String!
  content: String
}

type Query {
  user(id: ID!): User
  users: [User!]!
}

type Mutation {
  createPost(input: CreatePostInput!): Post!
}

Enums and Interfaces

enum Status {
  DRAFT
  PUBLISHED
  ARCHIVED
}

interface Node {
  id: ID!
}

type Article implements Node {
  id: ID!
  title: String!
}

Resolvers Overview

Resolvers follow the signature: (parent, args, contextValue, info)

• parent: Result from parent resolver (root resolvers receive undefined)
• args: Arguments passed to the field
• contextValue: Shared context object (auth, dataSources, etc.)
• info: Field-specific info and schema details (rarely used)

const resolvers = {
  Query: {
    user: async (_, { id }, { dataSources }) => {
      return dataSources.usersAPI.getUser(id);
    },
  },
  User: {
    posts: async (parent, _, { dataSources }) => {
      return dataSources.postsAPI.getPostsByAuthor(parent.id);
    },
  },
  Mutation: {
    createPost: async (_, { input }, { dataSources, user }) => {
      if (!user) throw new GraphQLError('Not authenticated');
      return dataSources.postsAPI.create({ ...input, authorId: user.id });
    },
  },
};

Context Setup

Context is created per-request and passed to all resolvers.

interface MyContext {
  token?: string;
  user?: User;
  dataSources: {
    usersAPI: UsersDataSource;
    postsAPI: PostsDataSource;
  };
}

const server = new ApolloServer<MyContext>({
  typeDefs,
  resolvers,
});

// Standalone
const { url } = await startStandaloneServer(server, {
  context: async ({ req }) => {
    const token = req.headers.authorization || '';
    const user = await getUser(token);
    return {
      token,
      user,
      dataSources: {
        usersAPI: new UsersDataSource(),
        postsAPI: new PostsDataSource(),
      },
    };
  },
});

// Express middleware
expressMiddleware(server, {
  context: async ({ req, res }) => ({
    token: req.headers.authorization,
    user: await getUser(req.headers.authorization),
    dataSources: {
      usersAPI: new UsersDataSource(),
      postsAPI: new PostsDataSource(),
    },
  }),
});

Reference Files

Detailed documentation for specific topics:

• Resolvers - Resolver patterns and best practices
• Context and Auth - Authentication and authorization
• Plugins - Server and request lifecycle hooks
• Data Sources - RESTDataSource and DataLoader
• Error Handling - GraphQLError and error formatting
• Troubleshooting - Common issues and solutions

Key Rules

Schema Design

• Use ! (non-null) for fields that always have values
• Prefer input types for mutations over inline arguments
• Use interfaces for polymorphic types
• Keep schema descriptions for documentation

Resolver Best Practices

• Keep resolvers thin - delegate to services/data sources
• Always handle errors explicitly
• Use DataLoader for batching related queries
• Return partial data when possible (GraphQL's strength)

Performance

• Use @defer and @stream for large responses
• Implement DataLoader to solve N+1 queries
• Consider persisted queries for production
• Use caching headers and CDN where appropriate

Ground Rules

• ALWAYS use Apollo Server 4.x patterns (not v3 or earlier)
• ALWAYS type your context with TypeScript generics
• ALWAYS use GraphQLError from graphql package for errors
• NEVER expose stack traces in production errors
• PREFER startStandaloneServer for simple setups
• USE expressMiddleware with drain plugin for Express apps
• IMPLEMENT authentication in context, authorization in resolvers