API / Apollo Gateway Interview questions
How do you implement custom middleware or plugins in Apollo Gateway?
Apollo Gateway doesn't have a plugin system of its own separate from Apollo Server — the main extension point for touching outgoing subgraph requests and incoming subgraph responses is overriding buildService to supply a custom RemoteGraphQLDataSource.
const { ApolloGateway, RemoteGraphQLDataSource } = require('@apollo/gateway'); class AuthenticatedDataSource extends RemoteGraphQLDataSource { willSendRequest({ request, context }) { request.http.headers.set('authorization', context.token || ''); } didReceiveResponse({ response, request, context }) { return response; } } const gateway = new ApolloGateway({ buildService({ url }) { return new AuthenticatedDataSource({ url }); }, });
willSendRequest is the hook most commonly used — forwarding auth headers, adding tracing headers, or attaching request-scoped context to each outgoing subgraph call. didReceiveResponse is available for inspecting or transforming what comes back before it's stitched into the final result.
Which class do you typically extend to customize outgoing subgraph requests in Apollo Gateway?
Which hook is most commonly used to forward auth headers to subgraphs?
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