Stateful Stream Processing Containerized as Microservice to Support Digital Twins in Fog Computing

Digital twins of processes and devices use information from sensors to synchronize their state with the entities of the physical world. The concept of stream computing enables effective processing of events generated by such sensors. However, the need to track the state of an instance of the object leads to the impossibility of organizing instances of digital twins as stateless services. Another feature of digital twins is that several tasks implemented on their basis require the ability to respond to incoming events at near-real-time speed. In this case, the use of cloud computing becomes unacceptable due to high latency. Fog computing manages this problem by moving some computational tasks closer to the data sources. One of the recent solutions providing the development of loosely coupled distributed systems is a Microservice approach, which implies the organization of the distributed system as a set of coherent and independent services interacting with each other using messages. The microservice is most often isolated by utilizing containers to overcome the high overheads of using virtual machines. The main problem is that microservices and containers together are stateless by nature. The container technology still does not fully support live container migration between physical hosts without data loss. It causes challenges in ensuring the uninterrupted operation of services in fog computing environments. Thus, an essential challenge is to create a containerized stateful stream processing based microservice to support digital twins in the fog computing environment. Within the scope of this article, we study live stateful stream processing migration and how to redistribute computational activity across cloud and fog nodes using Kafka middleware and its Stream DSL API.