This work presents an architecture that allows Information Systems to function even in moments of network disconnection, using a Healthcare Unit (HCU, from the Portuguese Unidade Municipal de Saúde - UMS) as a use case. The architecture uses a blockchain as a distributed database and one of its nodes (proxy node) is physically located inside an HCU, connected to its Local Area Network (LAN). During moments of disconnection between the LAN and the Internet, the proxy node continues handling query requests made by authenticated users on the LAN, functioning as a fog layer. It is also possible to generate new data and, with the help of a reliable oracle, write it to a local database. In these disconnection periods, the architecture explores the blockchain node's behavior and an oracle's functionality to record newly generated data. This approach makes it possible to guarantee the authenticity of the queried data. It is also possible to aggregate enough information about the new generated data to guarantee its integrity. Moreover, this information ensures the traceability and auditability of this data. An architecture prototype was implemented and used for execution tests. The test results show that the proposed architecture can maintain the information system working properly during a network outage. Therefore, the architecture increases the system resilience, being its application suitable for a smart city scenario, where data availability is desired.
Festa et al. (Fri,) studied this question.