  The heterogeneous, geographically distributed infrastructure of fog computing
poses challenges in data replication, data distribution, and data mobility for
fog applications. Fog computing is still missing the necessary abstractions to
manage application data, and fog application developers need to re-implement
data management for every new piece of software. Proposed solutions are limited
to certain application domains, such as the IoT, are not flexible in regard to
network topology, or do not provide the means for applications to control the
movement of their data.
  In this paper, we present FReD, a data replication middleware for the fog.
FReD serves as a building block for configurable fog data distribution and
enables low-latency, high-bandwidth, and privacy-sensitive applications. FReD
is a common data access interface across heterogeneous infrastructure and
network topologies, provides transparent and controllable data distribution,
and can be integrated with applications from different domains. To evaluate our
approach, we present a prototype implementation of FReD and show the benefits
of developing with FReD using three case studies of fog computing applications.
