How can we improve the efficiency of an existing web application? We could completely rewrite it, leverage more concurrency and even reactive features. But is it really worth it if we don’t even measure and track the relevant metrics? In this talk, Stéphane will work on an existing Spring Boot MVC application to make it more efficient. He’ll replace `RestTemplate` with `WebClient` and use Reactor operators to improve efficiency, without the concurrency pitfalls. He’ll use out-of-the-box metrics, add new ones to measure, and keep an eye on capacity gains with dashboards.