Apollo Federation Schema Authoring

Apollo Federation enables composing multiple GraphQL APIs (subgraphs) into a unified supergraph.

Federation 2 Schema Setup

Every Federation 2 subgraph must opt-in via @link:

extend schema
  @link(url: "https://specs.apollo.dev/federation/v2.12",
        import: ["@key", "@shareable", "@external", "@requires", "@provides"])

Import only the directives your subgraph uses. The version shown (v2.12) is illustrative — check the Federation changelog for currently supported versions before copying it verbatim.

A subgraph's @link version is a floor, not the composition version — see
[Federation versions](references/composition.md#federation-versions-floor-vs-composition)
for the full explanation.

Core Directives Quick Reference

Reference Files

Detailed documentation for specific topics:

• [Directives](references/directives.md) - All federation directives with syntax, examples, and rules
• [Schema Patterns](references/schema-patterns.md) - Multi-subgraph patterns and recipes
• [Composition](references/composition.md) - Composition rules, error codes, and debugging

Key Patterns

Entity Definition

type Product @key(fields: "id") {
  id: ID!
  name: String!
  price: Int
}

Entity Contributions Across Subgraphs

# Products subgraph
type Product @key(fields: "id") {
  id: ID!
  name: String!
  price: Int
}

# Reviews subgraph
type Product @key(fields: "id") {
  id: ID!
  reviews: [Review!]!
  averageRating: Float
}

Computed Fields with @requires

type Product @key(fields: "id") {
  id: ID!
  size: Int @external
  weight: Int @external
  shippingEstimate: String @requires(fields: "size weight")
}

Value Types with @shareable

type Money @shareable {
  amount: Int!
  currency: String!
}

Entity Stub (Reference Without Contributing)

type Product @key(fields: "id", resolvable: false) {
  id: ID!
}

Ground Rules

• ALWAYS use Federation 2.x syntax with @link directive
• ALWAYS import only the directives your subgraph uses
• NEVER use @shareable without ensuring all subgraphs return identical values for that field
• PREFER @key with single ID field for simple entity identification
• USE rover supergraph compose to validate composition locally
• USE rover subgraph check to validate against production supergraph