Model Checking the Safety of Raft Leader Election Algorithm

With the wide application of the Raft consensus algorithm in blockchain systems, its safety has attracted more and more attention. However, although some researchers have formally verified the safety of the Raft consensus algorithm in most scenarios, there are still some safety problems with Raft consensus algorithm in some special scenarios, and cause problems now and then. For example, as a core part of the Raft consensus algorithm, the Raft leader election algorithm usually faces some safety problems in following scenarios: if the network communication between some nodes is abnormal, the leader node could be unstable or even cannot be elected, or the log entry cannot be updated, etc. In this paper, we model check the safety of the Raft leader election algorithm throughly using Spin. We use Promela language to model the Raft leader election algorithm and use Linear-time Temporal Logic (LTL) formulae to characterize three safety properties including stability, liveness, and uniqueness. The verification results show that the Raft leader election algorithm does not hold stability and liveness when some nodes are faulty and node log entries are inconsistent. For these safety problems, we give the suggestions for improving safety by analyzing counter examples.