Achieving fault tolerance through replication techniques

Abstract

We study various replication techniques that can be applied to a web server in client-server architecture to achieve fault tolerance. Two different types of server, stateless and stateful, are replicated in a distributed environment using a concurrency oriented programming language and tested for criteria such as reliability and correctness in a failure-induced environment. Two already existent replication schemes, active replication and passive replication, are implemented along with a proposed replication scheme named Active-Passive Hybrid Replication. We highlight borderline cases due to replica failures for each replication scheme, and implement a correct solution to avoid potential race conditions. The three replication implementations are compared and evaluated for various characteristics including complexities of the interface and replicas, error handling mechanisms, and responsiveness in the presence of failures.