Next generation network nodes are required to function within heterogeneous network environments, where new services and protocols are rapidly deployed on demand. In such emerging environments, traditional node architectures that offer a predetermined and preloaded set of services, are increasingly incapable of coping with these new requirements. Accordingly, there is a need for new node architectures that offer higher degrees of flexibility measured by their capability to extend the functionality of the node and change its behaviour on demand. This paper makes use of programmable and active network technologies as developed during the FAIN project, to present a novel secure active node architecture, called the FAIN node architecture, capable of supporting virtual environments (VEs) for the allocation of the required amount of resources in which new services are dynamically deployed together with their entire execution environments (EEs). To this end, multiple VEs and services run simultaneously and interact securely with the node resources and mechanisms through open interfaces and the FAIN node management framework. We also present the implementation of the FAIN node architecture and two case studies that demonstrate its extensibility aspects and novel features.