Towards smarter IoT through taxonomy and prospective directions for microservices placement in fog computing paradigms

The integration of fog computing and microservice architecture (MSA) is transforming the deployment of Internet of Things (IoT) applications by enabling scalable, low-latency, resource-efficient solutions at the network edge. This review thoroughly explores the relationship between MSA and fog computing, focusing on the dynamic placement of microservice-based IoT applications. We introduce a novel taxonomy that classifies placement strategies according to adaptability, QoS awareness, energy efficiency, security, and orchestration complexity. Through a systematic review of more than 50 peer-reviewed studies published between 2018 and 2025, we identified significant research gaps, including limited support for hybrid fog-cloud elasticity, insufficient attention to distributed security and privacy, and underdeveloped resource management for heterogeneous edge nodes. This review also highlights the emerging influence of technologies such as quantum computing, digital twins, and net-zero emission frameworks. By synthesizing state-of-the-art methods, practical case studies, and future research directions, this study provides actionable guidelines for optimizing microservice placement and orchestration in fog-IoT ecosystems, serving as a roadmap for researchers and practitioners aiming to advance next-generation IoT applications.