---
title: Distributed Locking, Redlock, and Consistent Hashing on AWS
description: Redlock debates matter because ElastiCache is not a consensus system. Consistent hashing for sharding workers and ALB target stickiness—with DynamoDB conditional writes as the boring alternative.
url: https://www.factualminds.com/blog/distributed-coordination-redlock-consistent-hashing-elasticache/
datePublished: 2026-06-12T00:00:00.000Z
dateModified: 2026-06-12T00:00:00.000Z
author: Palaniappan P
category: Cloud Architecture
tags: engineering-guide, distributed-systems, elasticache, aws
---

# Distributed Locking, Redlock, and Consistent Hashing on AWS

> Redlock debates matter because ElastiCache is not a consensus system. Consistent hashing for sharding workers and ALB target stickiness—with DynamoDB conditional writes as the boring alternative.

**Martin Kleppmann’s critique (still valid June 2026):** Redis-based **Redlock** does not provide the same guarantees as Raft—clock skew and TTL expiry create false confidence.

## AWS-aligned coordination

| Need            | Prefer                                           | Avoid                                      |
| --------------- | ------------------------------------------------ | ------------------------------------------ |
| Mutex           | DynamoDB conditional update with lease attribute | Redlock across ElastiCache primary/replica |
| Leader election | ECS/EKS lease + DynamoDB lock item               | Infinite TTL without fencing token         |
| Work routing    | Consistent hash on `hash(user_id) % N`           | Random assign breaking cache locality      |

**Consistent hashing** minimizes remapping when nodes change—use for worker pools, Kafka partition keys, ALB sticky sessions (with failover caveats).

## ElastiCache locking

If you must use Redis locks: **short TTL**, **fencing tokens** passed to downstream (DB version check), monitor `WAIT` latency.

## What to do this week

1. Replace `SETNX` cron leader with DynamoDB `LockID` conditional put.
2. Document hash ring behavior on worker scale events.
3. Load test lock holder crash during write.

## What this guide doesn't cover

Paxos/Raft theory—next guide in track.

---

*Source: https://www.factualminds.com/blog/distributed-coordination-redlock-consistent-hashing-elasticache/*