In the development of many software systems, the focus was on functionality. When these systems begin to be used in situations requiring higher reliability and availability, such qualities must be retrofitted into the system. This paper considers way of adding such capability to existing software by taking advantage of aspect-oriented programming, recently developed technology which supports encapsulation of non-functional concerns. The paper introduces the notion of system health index as measure of the internal system well-being, and identifies number of health indictors, i.e. operational metrics from which health index could be derived. The paper then discusses inspect-oriented implementation of health indicators and lists several applicable aspect-oriented design patterns. Experience obtained from the implementation of health indicators in distributed system whose original development focused only on functionality is then summarized. The experience suggests that the time and space overhead and development costs are moderate, and that there is distinct advantage to the aspect-oriented implementation of health indicators.