Let teams own and deploy domain-specific subgraphs independently.
Large organizations
GraphQL · Const
federation
GraphQL federation combines independently managed subgraphs into one schema exposed through a gateway. Clients query the unified schema while the gateway routes work to the responsible services.
How it works
Federation divides a GraphQL API across independently managed subgraphs. A gateway composes their schemas into one schema for clients, routes query portions to the relevant services, gathers the results, and returns one response.
Returns
A unified GraphQL schema and, at runtime, a single response assembled from results returned by the relevant subgraphs.
Key points
- Federation lets independently managed services collaborate without requiring them to become one deployable application.
- Clients see one GraphQL schema even though its fields are implemented by multiple subgraphs.
- A subgraph should own a coherent domain or portion of the overall data graph.
- The gateway is the central entry point that coordinates composition and distributed query execution.
- Composition merges subgraph definitions into the schema exposed to clients.
- A query spanning domains is split and routed to the services responsible for its requested data.
Common mistakes
- The gateway is a runtime coordinator, so it must be deployed and operated as an additional service between clients and subgraphs.
Example: Entity in a subgraph
type Product @key(fields: "upc") {
upc: String!
name: String!
}A subgraph can define a product entity using a key field so the gateway can connect it with related data from other subgraphs.
When to use it
Present many services through one consistent GraphQL entry point.
Microservice architectures
Assemble data from multiple services into one client response.
Cross-domain queries
Use composition and a registry to validate relationships and compatibility.
Schema governance
Interview questions
QWhat is GraphQL federation?
Federation organizes a GraphQL API as multiple independent subgraphs, each owning part of the data graph. A gateway composes those schemas into a unified schema that clients query.
Follow-up: What happens when a client query spans services? The gateway divides the work among the appropriate subgraphs, collects their results, and assembles one response.
QWhat are the main components of a federated GraphQL system?
A subgraph is an individual service with its own GraphQL schema and resolvers. Schema composition combines subgraph schemas and resolves the relationships between them.
Follow-up: Why is composition necessary? It detects incompatibilities and ensures types are connected correctly before the gateway exposes the combined schema.
QHow would you introduce federation into an existing system?
Start by defining service boundaries, designing schemas around those boundaries, implementing the subgraphs, and deploying a gateway. A schema registry can manage composition and validation.
Follow-up: What operational concern does a registry address? It helps verify schema integrity as independently deployed subgraphs change.
Related
subgraphsgatewayschema compositionschema registryunified schema