Answers

1. Yes, it is required only if you need vertical scaling. In the cloud, you pay to use the resources, and reactive applications help you to use resources optimally. This is a new way of achieving scale. You need a small number of threads compared to non-reactive applications. The cost of connection to a database, I/O, or any external source is a callback; therefore, reactive-based applications do not require much memory. However, while reactive programming is superior in terms of vertical scaling, you should continue using your existing or non-reactive applications. Even Spring recommends that. There is no new or old style; both can co-exist. However, when you need scaling for any special component or application, you can go the reactive way. A few years back, Netflix replaced the Zuul API gateway with the reactive Zuul2 API gateway. This helped them to achieve scale. However, they still have/use non-reactive applications.
2. There are pros and cons to everything. Reactive...