# Building a Distributed Lock Service

Implementing distributed locks for coordinating across multiple servers.


**Model:** claude-opus-4
**Created:** 7/30/2026

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## Conversation

### **Human**

I need to implement a distributed lock so multiple servers don't process the same job. What's the right way to do this?

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### **Assistant**

Distributed locks are harder than they look! Let's build this properly:

THE PROBLEM:
10 servers processing jobs from a queue. Job #42 might be grabbed by 2 servers simultaneously. Need coordination: Only one server processes this job.

NAIVE APPROACH (FAILS):
if not job.locked then job.locked equals true, processJob(job).

Both servers see unlocked at the same time, double processing!

THE SOLUTION: REDIS LOCK (Redis Distributed Lock)

Try to acquire lock using SET NX EX (only set if not exists, with expiration). Return unique identifier if acquired.

WHY THIS WORKS:
1. Atomic: SET NX is atomic in Redis
2. Safe: Auto-expire prevents deadlocks
3. Unique: Each lock holder gets unique token

RELEASING THE LOCK:
Only release if we own it (use Lua script for atomicity). Check if the lock value matches our token, if yes then delete.

Using it:
acquireLock(job-42, 30). If acquired, try processing, finally release the lock.

Want to implement the full fault-tolerant version with multiple Redis nodes?

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*Downloaded from BranchLM - GitHub for AI Sessions*