A dynamic load balancing method for MQTT shared subscriptions considering the state of a group of subscribers

The MQTT Version 5.0 specification, developed in 2019, introduces shared subscriptions to distribute messages among multiple subscribers, improving the scalability and availability of MQTT-based data infrastructures. However, the current subscriber selection method for shared subscriptions is implementation-dependent, and many vendor products and open-source software only support static load balancing methods. Static load balancing methods cannot adapt to the changes in subscriber data processing performance due to the influence of other workloads, potentially leading to processing delays for the overall workload. In this study, we propose a method to achieve dynamic load balancing for shared subscriptions by managing the state of a group of subscribers connected to the broker in real-time. Our proposed method extends the MQTT Control Packet to enable dynamic load balancing based on the number of pending messages by transmitting the status of subscriber message processing to the broker at any time. The evaluation results demonstrate that the proposed method reduces the latency of the overall workload by 98% compared to the existing static load balancing methods.