  Internet-of-Things (IoT) ecosystems tend to grow both in scale and complexity
as they consist of a variety of heterogeneous devices, which span over multiple
architectural IoT layers (e.g., cloud, edge, sensors). Further, IoT systems
increasingly demand the resilient operability of services as they become part
of critical infrastructures. This leads to a broad variety of research works
that aim to increase the resilience of these systems. In this paper, we create
a systematization of knowledge about existing scientific efforts of making IoT
systems resilient. In particular, we first discuss the taxonomy and
classification of resilience and resilience mechanisms and subsequently survey
state-of-the-art resilience mechanisms that have been proposed by research work
and are applicable to IoT. As part of the survey, we also discuss questions
that focus on the practical aspects of resilience, e.g., which constraints
resilience mechanisms impose on developers when designing resilient systems by
incorporating a specific mechanism into IoT systems.
