Redis Distributed Locking in Spring Boot: Stop Duplicate Processing

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As applications evolve from monoliths to distributed systems, a new class of problems appears:

• Race conditions
• Duplicate processing
• Concurrent updates

Everything works fine with one running instance. But what happens when Pod-1, Pod-2, Pod-3 and Pod-4 all receive the same request at the same moment?

This is where Redis distributed locking becomes valuable.

In this article, we’ll cover:

• What distributed locking is and why synchronized doesn't work in microservices
• Redis SET NX PX
• Safe lock acquisition and release (with a Lua script)
• Preventing duplicate processing
• Banking and payment examples (and why a lock alone isn’t enough)
• Lock expiry, renewal and fencing tokens
• Redisson, RedLock and when not to use Redis locks

The Real Problem

Suppose your system processes customer rewards.

POST /rewards/process

{
  "customerId": "123",
  "rewardAmount": 500
}