Crash-Resilient Decentralized Synchronous Runtime Verification

Runtime verification is a technique, where a monitor process extracts information from a running system in order to evaluate whether system executions violate or satisfy a given correctness specification. In this article, we consider runtime verification of synchronous distributed systems, where a set of decentralized monitors that only have a partial view of the system are subject to crash failures. In this context, it is unavoidable that monitors may have different views of the underlying system, and, therefore, have different opinions about the correctness property. We propose an automata-based synchronous monitoring algorithm that copes with $t$t crash monitor failures. In our proposed approach, local monitors do not communicate their explicit reading of the underlying system. Rather, they emit a symbolic verdict that efficiently encodes their partial views. This significantly reduces the communication overhead. To this end, we also introduce an (offline) SMT-based monitor synthesis algorithm, which results in minimizing the size of monitoring messages. We evaluate our algorithm on a wide range of formulas and observe an average of 2.5 times increase in the number of states of the monitor automaton.