Paxos made transparent

State machine replication (SMR) leverages distributed consensus protocols such as Paxos to keep multiple replicas of a program consistent in face of replica failures or network partitions. This fault tolerance is enticing on implementing a principled SMR system that replicates general programs, especially server programs that demand high availability. Unfortunately, SMR assumes deterministic execution, but most server programs are multithreaded and thus nondeterministic. Moreover, existing SMR systems provide narrow state machine interfaces to suit specific programs, and it can be quite strenuous and error-prone to orchestrate a general program into these interfaces This paper presents Crane, an SMR system that transparently replicates general server programs. Crane achieves distributed consensus on the socket API, a common interface to almost all server programs. It leverages deterministic multithreading (specifically, our prior system Parrot) to make multithreaded replicas deterministic. It uses a new technique we call time bubbling to efficiently tackle a difficult challenge of nondeterministic network input timing. Evaluation on five widely used server programs (e.g., Apache, ClamAV, and MySQL) shows that Crane is easy to use, has moderate overhead, and is robust. Crane's source code is at github.com/columbia/crane.