Modelling Adaptation Policies as Domain-Specific Constraints

In order to develop appropriate adaptation policies for self-adaptive systems, developers usually have to accomplish two main tasks: (i) identify the application-level constraints that regulate the desired system states for the various contexts, and (ii) figure out how to transform the system to satisfy these constraints. The second task is challenging because typically there is complex interaction among constraints, and a significant gap between application domain expertice and state transition expertice. In this paper, we present a model-driven approach that relieves developers from this second task, allowing them to directly write domain-specific constraints as adaptation policies. We provide a language to model both the domain concepts and the application-level constraints. Our runtime engine transforms the model into a Satisfiability Modulo Theory problem, optimises it by pre-processing on the current system state at runtime, and computes required modifications according to the specified constraints using constraints solving. We evaluate the approach addressing a virtual machine placement problem in cloud computing.