Implement Distributed Locks with Spring Integration: Redis & Zookeeper Guide

Overview

When people talk about distributed locks, two common solutions are Redisson (Redlock algorithm) and Apache Curator (Zookeeper temporary sequential nodes). This article introduces a third approach using Spring Integration, which I recommend.

Spring Integration provides lightweight messaging for Spring applications and underlies Spring Cloud Stream. It offers a unified API for global locks backed by Gemfire, JDBC, Redis, and Zookeeper, allowing the same code to switch storage without changes.

Key Methods

lock()

: Acquires the lock; blocks if already held. lockInterruptibly(): Acquires the lock unless the thread is interrupted. tryLock(): Attempts to acquire the lock only if it is free; returns true on success. tryLock(long time, TimeUnit unit): Tries to acquire the lock within the given waiting time; returns true on success. unlock(): Releases the lock.

Practical Example

Redis Implementation

Add Maven dependencies for spring-boot-starter-integration, spring-integration-redis, and spring-boot-starter-data-redis.

Configure Redis connection in application.yml.

Create a @Configuration class that defines a RedisLockRegistry bean.

Write a @RestController with an endpoint /lock/redis that obtains a lock from the registry, tries to lock for 3 seconds, logs the result, sleeps for 5 seconds, and finally unlocks.

Run multiple instances and call the endpoint; only one instance obtains the lock, demonstrating distributed locking.

Note: When using newer Spring Boot versions, ensure Redis 4.x is used; otherwise the unlock() operation may fail because the UNLINK command is unsupported.

2020-05-14 11:30:24,781 WARN  RedisLockRegistry:339 - The UNLINK command has failed (not supported on the Redis server?); falling back to the regular DELETE command
org.springframework.data.redis.RedisSystemException: Error in execution; nested exception is io.lettuce.core.RedisCommandExecutionException: ERR unknown command 'UNLINK'

Zookeeper Implementation

Add Maven dependencies for spring-boot-starter-integration and spring-integration-zookeeper.

Configure Zookeeper connection in application.yml.

Create a @Configuration class that defines a CuratorFrameworkFactoryBean and a ZookeeperLockRegistry bean.

Write a @RestController with an endpoint /lock/zookeeper that obtains a lock from the Zookeeper registry, tries to lock for 3 seconds, logs, sleeps, and finally unlocks.

Run multiple instances and call the endpoint; only one instance acquires the lock, confirming the distributed lock works.