Real-Time Online Interactive Applications (ROIA), such as massively multi-player online games, e-Learning applications and high-performance real-time simulations, establish a rapidly growing commercial market and may potentially become a killer application class for future parallel and distributed systems including Clouds. ROIA pose several specific challenges as compared to typical (e.g., numerical) high-performance applications: a) huge numbers of users participating in a single application session (up to 104), b) low response times in order to deliver a real-time user experience (from 100 ms for fast-paced action games to 1.5s for role-playing games), and c) high update rate of the global application state (up to 50Hz).

In this paper, we aim at achieving scalability of ROIA, i.e. accommodating an increasing number of users by employing additional compute resources, on two major classes of target systems: distributed systems with multiple physical servers, and Cloud systems that provide distributed virtual resources. We develop a fine-grained model for the main performance metrics of ROIA, in particular the response time. We present our Real-Time Framework (RTF) – a development and execution platform for ROIA, and report experimental results on the scalability of RTF-based ROIA and their responsiveness. An additional challenge of ROIA is the changing (e.g., daytime-dependent) load: statically assigned servers may either not cope with the peak user numbers or remain underutilized when these numbers are low. We address this challenge by extending RTF with dynamic management tools which allow us to efficiently use virtual Cloud resources, and report our preliminary experiments on the performance of ROIA execution on the Amazon EC2 Cloud system.