Debugging subgraph requests from the Apollo Router or @apollo/gateway

As your graph grows, you may need to debug a problematic query for one reason or another. The

Each client request goes through a process called

Output query plans with headers

With

• Including the Apollo-Query-Plan-Experimental header returns the query plan in the response extensions
• Additionally, including the Apollo-Query-Plan-Experimental-Format header with one of the supported options changes the output format:
  • A value of prettified returns a human-readable string of the query plan
  • A value of internal returns a JSON representation of the query plan

Log Apollo Router subgraph calls

If, instead, you want to debug your subgraph HTTP requests in an Apollo Router instance, you can use

1
fn subgraph_service(service, subgraph) {
2
  service.map_request(|request| {
3
      log_info(`Subgraph: ${subgraph} Query: ${request.subgraph.body.query}`);
4
  });
5
}

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 must run the Apollo Router with the --dev flag and leverage

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

1
plugins:
2
  experimental.expose_query_plan: true

Log @apollo/gateway subgraph calls

To debug queries to your subgraphs within an @apollo/gateway instance, you can use a

1
class DebugDataSource extends RemoteGraphQLDataSource {
2
  willSendRequest({
3
    request
4
  }: GraphQLDataSourceProcessOptions<
5
    Record<string, any>
6
  >): void | Promise<void> {
7
    console.log(`Operation name: ${request.operationName}`);
8
    console.log(`Query body: ${request.query}`);
9
  }
10
}
11
const gateway = new ApolloGateway({
12
  debug: true,
13
  supergraphSdl,
14
  buildService({url}) {
15
    return new DebugDataSource({url});
16
  }
17
});

The above snippet creates a new class called DebugDataSource to log out the operation name and body using the willSendRequest hook, which is called before 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.