Understanding Distributed Locking: A Deep Dive into RedLock with Redis

Introduction to Locking

Locking is a fundamental concept in computing, ensuring that resources are accessed safely in concurrent environments. It prevents race conditions where multiple processes or threads try to modify shared data simultaneously.

Types of Locking

1. Centralized Locking:
   • A single server manages all locks, ensuring consistency.
   • Used in databases (e.g., row-level locks in SQL databases).
2. Distributed Locking:
   • Used when multiple nodes need synchronized access to shared resources.
   • Ensures coordination across distributed systems.

Advantages and Disadvantages of Centralized Locking

Advantages:

✅ Simple to implement.
✅ Low network latency as all requests go to one server.

Disadvantages:

❌ Single point of failure (if the central lock manager goes down).
❌ Not scalable for high-traffic distributed systems.

Why is Distributed Locking Needed?

Consider a scenario where an e-commerce platform runs on multiple servers. If two users try to buy the last available product, both transactions might proceed simultaneously, leading to overselling. Distributed locking ensures that only one transaction completes at a time, preventing inconsistencies.

Introduction to Distributed Locking

A distributed lock ensures mutual exclusion across multiple nodes in a distributed system. It requires a highly available, fault-tolerant, and consistent locking mechanism.

Types of Distributed Locking Mechanisms

1. Database-based Locks: Using a database (SQL/NoSQL) to manage locks.
2. Zookeeper-based Locks: Apache Zookeeper provides distributed coordination services.
3. Redis-based Locks: Using Redis to create fast and reliable distributed locks.

Introduction to RedLock by Redis

RedLock is a distributed locking algorithm developed by Redis to solve issues with single-instance Redis locks. It ensures safety, liveness, and fault tolerance in distributed environments by using multiple Redis instances.

How RedLock Works?

1. Acquire a lock on at least N/2 + 1 Redis instances.
2. If successful, the lock is granted.
3. If unsuccessful, release any acquired locks and retry.

Implementation of RedLock in Spring Boot (Using Redisson)

Maven Dependency

<dependency>
    <groupId>org.redisson</groupId>
    <artifactId>redisson</artifactId>
    <version>3.16.1</version>
</dependency>

Redisson Configuration

@Configuration
public class RedissonConfig {

    @Bean
    public RedissonClient redissonClient() {
        Config config = new Config();
        config.useReplicatedServers()
              .addNodeAddress("redis://127.0.0.1:6379", "redis://127.0.0.2:6379");
        return Redisson.create(config);
    }
}

Using Redisson for Distributed Locking

@Service
public class DistributedLockService {

    @Autowired
    private RedissonClient redissonClient;

    public void performTaskWithLock() {
        RLock lock = redissonClient.getLock("my_lock");

        if (lock.tryLock()) {
            try {
                System.out.println("Lock acquired! Processing...");
                // Critical section
            } finally {
                lock.unlock();
                System.out.println("Lock released!");
            }
        } else {
            System.out.println("Failed to acquire lock!");
        }
    }
}

Benefits and Disadvantages of RedLock

Benefits:

✅ Fault tolerance with multiple Redis instances.
✅ Ensures safety and prevents deadlocks.
✅ High availability with automatic retries.

Disadvantages:

❌ Requires multiple Redis nodes, increasing infrastructure complexity.
❌ Slightly higher latency compared to single-instance Redis locks.

References to Consider

Redis Official Documentation
Redisson GitHub Repository