The Raft Consensus Algorithm and
Implementing Raft in C++

Diego Ongaro, August 2015

LogCabin

• Started as research platform for Raft at Stanford
• Developed into production system at Scale Computing
• Network service running Raft replicated state machine
• Data model: hierarchical key-value store
• Written in gcc 4.4's C++0x (Rust was pre-0.1)

How Is Consensus Used?

Top-level system configuration

Replicate entire database state

Paxos Protocol

• Leslie Lamport, 1989
• Nearly synonymous with consensus

“The dirty little secret of the NSDI community is that at most five people really, truly understand every part of Paxos ;-).”
—NSDI reviewer

“There are significant gaps between the description of the Paxos algorithm and the needs of a real-world system...the final system will be based on an unproven protocol.”
—Chubby authors

Raft's Design for Understandability

We wanted an algorithm optimized for building real systems

• Must be correct, complete, and perform well
• Must also be understandable

“What would be easier to understand or explain?”

• Fundamentally different decomposition than Paxos
• Less complexity in state space
• Less mechanism

Raft User Study

Raft Implementations