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
$t$
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.