Software evolution is a major challenge to software development. When adapting a component-based system to new, altered or deleted requirements, existing requirements should not accidentally be violated. Invariant conditions are usually specified via constraint languages like OCL on a high precision level close to source code. On the contrary, this paper uses a new constraint mechanism. One context-based constraint (CoCon) specifies one requirement for a group of indirectly associated components that share a context. This paper proposes a ‘Rule Manager’ approach to monitor a system’s compliance with requirements automatically at runtime. The approach is compatible with modern middleware technologies and allows the transparent integration of requirement validation in legacy systems or COTS.