Micro-controllers: Promoting Structurally Flexible Controllers in Self-Adaptive Software Systems.

To promote structurally flexible controllers in self-adaptive software systems, this paper proposes the use of micro-controllers. Instead of generic monolithic controllers, like Rainbow, we advocate the use of service-specific micro-controllers which can be based on microservices. Although traditional generic controllers can be configured parametrically according to system needs, their use and reuse are nevertheless restrictive because of the wide range of services expected from the different stages of the feedback control loop.The solution being advocated is to have structurally flexible controllers that can be composed from micro-controllers. Controlling the architectural configuration of these micro-controllers is a meta-controller that is able to configure the controller according to the services required for controlling the target system. The feasibility of the proposed approach of using micro-controllers at the level of the controller is demonstrated in the context of the PhoneAdapter case study in which micro-controllers are configured at run-time depending on changes affecting the system or its environment.