In this paper, we address the crucial issue of online software adaptation: how to determine if the system is in an adaptable state? To solve this issue, we advocate the use of both Component-Based Software Engineering (CBSE) and reflective technologies. Such technologies enable a metamodel of the software architecture to be established to represent both structural and behavioral aspects. Based on some requirements expressed by the software designer, and using online animation of the software model (CBSE metamodels and Petri Nets), we propose an approach to 1/decide when the system (or a sub-system) is adaptable, and 2/ guide the system towards an adaptable state. Finally, this approach is applied to the online adaptation of replication mechanisms on a small case study.