To effectively monitor and analyze the performance of modern applications, it's crucial to customize events and reporting. The Apollo Router offers a toolkit for collecting and reporting data from an application's request lifecycle through telemetry events and instruments. Telemetry events signal significant occurrences in the request lifecycle, providing visibility into what happens during processing. Custom events can be configured to capture specific moments of interest, while standard events are available for logging requests, responses, and errors. Instruments allow for collecting metrics such as active requests, request body size, request duration, and response body size. Custom instruments can also be defined to collect specific metrics relevant to the application. By combining telemetry events and instruments, developers can gain valuable insights into their application's behavior, troubleshoot issues, and optimize performance.