Large-scale Internet of Things (IoT) services such as healthcare, smart cities, and marine monitoring are pervasive in cyber-physical environments. These complex IoT services are increasingly composed of sensors, devices, and compute resources within fog computing infrastructures. Orchestrating such applications can simplify maintenance and enhance data security and system reliability. However, efficiently dealing with these services' dynamic variations and transient operational behavior is a crucial challenge. This article provides an overview of the core issues, challenges, and future research directions in fog-enabled orchestration for IoT services.