5장: Federation과 Supergraph

# Users 서브그래프 — User 엔티티의 소유자
type User @key(fields: "id") {
  id: ID!
  name: String!
  email: String!
  avatar: String
}
 
type Query {
  user(id: ID!): User
  me: User
}

# Reviews 서브그래프 — User 엔티티를 확장
type User @key(fields: "id") {
  id: ID!
  reviews: [Review!]!    # 이 서브그래프가 추가하는 필드
}
 
type Review @key(fields: "id") {
  id: ID!
  rating: Int!
  body: String!
  author: User!
  product: Product!
}

// Users 서브그래프
const resolvers = {
  User: {
    __resolveReference: async (
      reference: { __typename: 'User'; id: string },
      context: Context,
    ) => {
      // 4장에서 배운 DataLoader 사용이 필수
      return context.loaders.userById.load(reference.id);
    },
  },
};

query {
  me {
    name          # Users 서브그래프
    email         # Users 서브그래프
    reviews {     # Reviews 서브그래프
      rating
      body
      product {   # Products 서브그래프
        name
        price
      }
    }
  }
}

# 단일 키
type User @key(fields: "id") {
  id: ID!
  name: String!
}
 
# 복합 키
type ProductVariant @key(fields: "productId sku") {
  productId: ID!
  sku: String!
  price: Int!
}
 
# 다중 키 (여러 방법으로 식별 가능)
type User @key(fields: "id") @key(fields: "email") {
  id: ID!
  email: String!
  name: String!
}

# Reviews 서브그래프
type Product @key(fields: "id") {
  id: ID!
  averageRating: Float! @requires(fields: "reviewCount totalRating")
  reviewCount: Int! @external
  totalRating: Int! @external
}

# Reviews 서브그래프
type Review @key(fields: "id") {
  id: ID!
  body: String!
  author: User! @provides(fields: "name")
}
 
# Reviews 서브그래프가 User.name을 직접 제공할 수 있음
type User @key(fields: "id") {
  id: ID!
  name: String! @external
}

# Shipping 서브그래프
type Product @key(fields: "id") {
  id: ID!
  weight: Float! @external
  dimensions: String! @external
  shippingCost: Float! @requires(fields: "weight dimensions")
}

import { ApolloServer } from '@apollo/server';
import { buildSubgraphSchema } from '@apollo/subgraph';
import { parse } from 'graphql';
import { readFileSync } from 'fs';
 
const typeDefs = parse(readFileSync('./schema.graphql', 'utf8'));
 
const resolvers = {
  Query: {
    user: async (_parent: unknown, args: { id: string }, context: Context) => {
      return context.dataSources.users.findById(args.id);
    },
    me: async (_parent: unknown, _args: unknown, context: Context) => {
      if (!context.currentUser) return null;
      return context.dataSources.users.findById(context.currentUser.id);
    },
  },
  User: {
    __resolveReference: async (
      ref: { __typename: 'User'; id: string },
      context: Context,
    ) => {
      return context.loaders.userById.load(ref.id);
    },
  },
};
 
const server = new ApolloServer({
  schema: buildSubgraphSchema({ typeDefs, resolvers }),
});

federation_version: =2.9
subgraphs:
  users:
    routing_url: http://localhost:4001/graphql
    schema:
      file: ./subgraphs/users/schema.graphql
  products:
    routing_url: http://localhost:4002/graphql
    schema:
      file: ./subgraphs/products/schema.graphql
  reviews:
    routing_url: http://localhost:4003/graphql
    schema:
      file: ./subgraphs/reviews/schema.graphql

# Rover CLI로 슈퍼그래프 스키마 생성
rover supergraph compose --config ./supergraph.yaml > supergraph.graphql
 
# 컴포지션 검증 (CI에서 사용)
rover supergraph compose --config ./supergraph.yaml --dry-run

# 서브그래프 스키마 변경 검증 (CI에서 실행)
rover subgraph check my-graph@production \
  --name users \
  --schema ./schema.graphql
 
# 서브그래프 스키마 배포 (CD에서 실행)
rover subgraph publish my-graph@production \
  --name users \
  --schema ./schema.graphql \
  --routing-url https://users.internal:4001/graphql

supergraph:
  listen: 0.0.0.0:4000
 
# 헤더 전파 설정
headers:
  all:
    request:
      - propagate:
          matching: "authorization|x-request-id|x-trace-id"
 
# CORS 설정
cors:
  origins:
    - https://app.example.com
  allow_headers:
    - Content-Type
    - Authorization
 
# 텔레메트리
telemetry:
  instrumentation:
    spans:
      mode: spec_compliant
  exporters:
    tracing:
      otlp:
        enabled: true
        endpoint: http://otel-collector:4317
 
# 쿼리 제한
limits:
  max_depth: 15
  max_height: 200
  max_aliases: 30