Debugging subgraph requests from Apollo Router or Gateway

Both the Apollo Router and Apollo Gateway serve as an entrypoint into your federated graph, and as your graph grows you may need to debug a problematic query for one reason or another.

It's possible to log the each request to your subgraphs in both the Gateway and Router, with code snippets to do so below.

Apollo Router

To debug your subgraph queries in an Apollo Router instance, we'll leverage Rhai to log the necessary information out. An example Rhai script is below.

Note that while it is possible to log out the variables, Apollo strongly recommends not doing so to avoid leaking sensitive information into your logs.

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fn subgraph_service(service, subgraph) {
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  service.map_request(|request| {
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      log_info(`Subgraph: ${subgraph} Query: ${request.subgraph.body.query}`);
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  });
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}

The above uses an inline closure within the map_request function of the subgraph_service hook to log the subgraph-related information.

To enable query plans, you will need to run the Apollo Router with the --dev flag and leverage Apollo Sandbox to display your query plans.

As an alternative to using --dev, you can also enable query plans via the below configuration option, however we strongly discourage this as the feature may be removed or renamed at any time in the future.

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plugins:
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  experimental.expose_query_plan: true

Apollo Gateway

To debug queries to your subgraphs within an Apollo Gateway instance, we'll leverage a buildService function to log the operation name and body.

Note that while it is possible to log out the variables, Apollo strongly recommends not doing so to avoid leaking sensitive information into your logs.

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class DebugDataSource extends RemoteGraphQLDataSource {
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  willSendRequest({ request }: GraphQLDataSourceProcessOptions<Record<string, any>>): void | Promise<void> {
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      console.log(`Operation name: ${request.operationName}`);
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      console.log(`Query body: ${request.query}`);
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  }
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}
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const gateway = new ApolloGateway({
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  debug: true,
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  supergraphSdl,
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  buildService({ url }) {
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      return new DebugDataSource({ url })
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  },
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});

The above snippet will create a new class called DebugDataSource to log out the operation name and body using the willSendRequest hook which is called prior to execution.

Lastly, it also enables the debug setting on the Gateway configuration to print out query plans in the logs for further debugging if needed.