Grails 3 sits on the shoulders of Spring Boot. There are many configuration options which are possible thanks to Spring Boot. We saw it in the latest issue with the @Value annotation for injecting config values.
From the Grails technologies, Spring has been always my weakest point. If you are looking for Spring Boot Courses, @therealdanvega has two courses. A free introductory course and more complete paid Spring Boot Intro.
Note: the free course includes a coupon code to make the paid course just 19$