Application monitoring and service metrics
If you don’t track it, you can’t measure it. Realtime service and business metrics should be part of any production application. Knowing how is the app performing is as important as measuring whether the product impact of your changes.
A good set of service metrics lets you effectively monitor the impact of your changes on the app performance. Has your change to multi-threading really achieved the times x throughput? Has the last dependency injection change caused a slow memory leak? Are there levels of response codes you’re not expecting in your app?