apollo-federation

To define an entity in an Apollo Federation subgraph schema, you apply the @key directive to a type and specify its unique identifier fields. This establishes the type as a shared object across your federated graph.

The best way to share types across subgraphs in Apollo Federation is by using the @shareable directive. This marks specific fields or types as resolvable by multiple subgraphs, ensuring seamless API composition within your supergraph.

To resolve schema composition errors in Apollo Federation 2.x, you must align conflicting directive usage and type definitions across subgraphs. Troubleshooting involves checking @external and @key implementations to ensure valid supergraph composition.

You need to use the @external directive in a GraphQL subgraph when you want to reference a field that is defined and owned by another subgraph. This allows your subgraph to access shared entity fields without redefining them.

Yes, you can use Apollo Federation directives for microservice API composition. By authoring subgraph schemas with directives like @provides and @key, you can seamlessly integrate multiple microservices into a single unified supergraph API.

Your subgraph schema fails when defining fields provided by another service because you likely omitted the @external directive. You must mark foreign-owned fields as external to prevent composition errors during supergraph schema merging.