Hi, is it still relevant, is it worth reading? I need to build time series stream analysis, raise alert if time series values vuolate threshold.

It depends.. the apis are somewhat outdated, but the concepts are still the same. You can read through to get a better understanding of the concepts and try reproducing the examples by trying to use the newer APIs where necessary. Another one up to date in video format is this

The book is excellent, especially the first few chapters - great introduction into stream processing.

If you want to understand how Flink works, there's still no better resource. And the DataStream API hasn't changed much since then either. Most of the improvements to Flink since 1.7 (the version that book is based on) are in the Table/SQL engine, changes to how deployments are usually done these days, and a host of refinements in the runtime.