Adaptive Failover for Real-Time Middleware with Passive Replication

Supporting uninterrupted services for distributed soft real-time applications is hard in resource-constrained and dynamic environments, where processor or process failures and system workload changes are common. Fault-tolerant middleware for these applications must achieve high service availability and satisfactory response times for client applications. Although passive replication is a promising fault tolerance strategy for resource-constrained systems, conventional client failover approaches are non-adaptive and load-agnostic, which can cause system overloads and significantly increase response times after failure recovery.This paper presents four contributions to the study of passive replication for distributed soft real-time applications. First, it describes how our fault-tolerant load-aware and adaptive middleware (FLARe) dynamically adjusts failover targets at runtime in response to system load fluctuations and resource availability. Second, it describes how FLARe´s overload management strategy proactively enforces desired CPU utilization bounds by redirecting clients from overloaded processors. Third, it presents the design and implementation of FLARe´s lightweight middleware architecture that manages failures and overloads transparently to clients. Finally, it presents experimental results on a distributed Linux testbed that demonstrate how FLARe adaptively maintains soft real-time performance for clients operating in the presence of failures and overloads with negligible runtime overhead.