Accountable Clouds Through Blockchain

We present a solution for accountability in Cloud infrastructures based on blockchain. We show that, through smart contracts, it is possible to create an unforgeable log that can be used for auditing and automatic Service Level Agreement (SLA) verification. As a practical case study, we consider Cloud storage services and define interaction protocols for registering the outcome of each file operation in the blockchain. We developed a prototype implementation that runs on the GoQuorum, Hyperledger Besu, and Polygon blockchains, using different consensus protocols. Using a dedicated testbed, we discuss the performance of our implementation in terms of latencies, error rates and gas usage. Results demonstrate the viability of our approach over permissioned blockchains, with better performance for the Polygon and GoQuorum Raft decentralized systems. Our implementation enables interoperability, given that it is supported by the Ethereum Virtual Machine which currently is underlying several blockchain platforms.