In this talk I show how to create a distributed lock using MongoDB and Node.js as a client (it works with any language/framework). The lock is modeled after the Redis’s Redlock algorithm and it tries to keep the same three minimum guarantess.

Safety property: Mutual exclusion. At any given moment, only one client can hold a lock.

Liveness property A: Deadlock free. Eventually it is always possible to acquire a lock, even if the client that locked a resource crashes or gets partitioned.

Liveness property B: Fault tolerance. As long as the majority of Redis nodes are up, clients are able to acquire and release locks.

This talk has been given, for the first time, in March 2025 at Rome MongoDB User Group.

Additional resources - links at the and of the talk

• Martin Kleppmann analisys of Redlock safety.
• Salvatore Sanfilippo counterpoint to this analysis.
• Square MongoDB locking library in Go.

My other (related) talks

• Alessandro Miliucci - Raft: the Hidden Algorithm that Powers the Cloud - October 2022 - English (signup wall - Codemotion)
• Alessandro Miliucci - The Raft Consensus Algorithm- September 2023 - Italian (Youtube - Come to Code 2023)
• Alessandro Miliucci - MongoDB Replication Explained - March 2023 - Italian (Youtube - Incontro DevOps Italia 2023)