High Availability for virtualized Programmable Logic Controllers with Hard Real-Time Requirements on Cloud Infrastructures

Cloud computing is becoming more popular in domains where previously hardware-based bare metal implementations dominated the field of computation workloads such as the automation and process industry. A variety of stateful applications exist that will require high availability on cloud infrastructures while also meeting the hard real-time requirements in the millisecond area of their superimposed processes, e.g., virtualized programmable logic controllers (vPLCs) and artificial intelligence inference services. This paper presents an approach for stateful applications on distributed systems to meet the application’s requirements in failover scenarios through state synchronization by means of Remote Direct Memory Access (RDMA). Experimental results with a software PLC confirm the effectiveness of the described approach in comparison to UDP-based synchronization, reducing the average synchronization time by up to 99.39%. The concept is suitable for applications on virtual machines and containers and might be an enabler for virtualization of real-time critical applications such as control functions in the automation and process industry.