What's supported

All core Federation v2 directives work out of the box:

- @key — simple, composite, nested ("coord { lat lng }"), multiple @key per type, @key(resolvable: false) - @external — correct ownership filtering; stub references (e.g. a service that declares a type only to satisfy a key) are never mistaken for entity owners - @requires — chained dependency injection resolved in topological order - @provides — skips unnecessary _entities fetches when the parent service already covers all requested child fields - @shareable — prefers the parent subgraph to avoid extra entity fetches - @override — field ownership migration between subgraphs - @inaccessible — enforced at both schema composition and query validation - @interfaceObject — interface types as entities with inline fragment resolution - @composeDirective — custom directive preservation with consistency validation - @tag, @link

Operations: query and mutation. Independent subgraph fetches run in parallel; mutations execute sequentially per the GraphQL spec. Partial responses are supported — a failed subgraph sets that field to null and appends an error, but execution continues for unaffected fields.

What's intentionally not supported

- Subscription — requires stateful WebSocket connections, which contradicts the stateless design. Every request is fully self-contained. - @authenticated / @requiresScopes / @policy — authorization belongs outside the gateway layer. - @defer / @stream — requires long-lived streaming connections. - Federated Tracing (ftv1) — Apollo Studio-specific protocol. - @override(label) — progressive override; planned for a future release.

Performance

Go's http.DefaultTransport caps MaxIdleConnsPerHost at 2, which was a hard throughput ceiling. The gateway defaults to 32 (configurable via gateway.yaml). Query plans are cached per query string.

  Go Gateway:    ~4,380 req/s
  Apollo Router: ~2,771 req/s  (concurrency 50, 10k requests, Docker networking)

GitHub: https://github.com/n9te9/go-graphql-federation-gateway

Happy to hear about Federation v2 edge cases you've hit in production.