This paper addresses the challenge of achieving reliable and predictable operation of flexible and modular pro-duction systems with distributed control and potentially wireless communication. Such systems are envisaged as common in the future Industry 4.0 production facilities. A software design pattern is proposed to implement online monitoring of requirements. The IEC 61499 architecture is selected as the implementation platform and its benefits are essentially used by utilisation of the adapter interface mechanism. The paper also outlines a pathway to designing and verifying the monitors based on formal methods.