Redis Implementation Guides

Redis is more than a cache. Its versatile data structures and atomic operations make it ideal for implementing common distributed system primitives like rate limiters, locks, queues, and counters. These patterns appear everywhere in production systems but are often implemented incorrectly or inefficiently.

This section provides practical guides for implementing these primitives with Redis. Each guide covers multiple approaches, explains the tradeoffs, and includes working code examples you can adapt for your own systems.

📄️ How to Implement Rate Limiting in Redis

Every API needs rate limiting, but not every API needs the same algorithm. The right choice depends on whether you want strict limits, smooth traffic, burst tolerance, or minimal memory usage. Redis can implement all the common approaches, each with different commands and tradeoffs.

📄️ How to Build a Scheduled Queue in Redis

Many applications need to process tasks at a specific time in the future rather than immediately. Email reminders that go out 24 hours before an event, retry logic that waits before trying again, subscription renewals that trigger on a billing date. These all require a scheduled queue: a way to store tasks now and process them later when their time comes.

📄️ How to Build a URL Shortener in Redis

URL shorteners turn long URLs into compact codes that redirect to the original destination. Behind every short link is a simple lookup: given a code like abc123, return the full URL. Redis excels at this because the core operation is a key-value lookup, and Redis handles millions of these per second with sub-millisecond latency.

📄️ How to Build a Distributed Lock in Redis

When multiple processes need exclusive access to a shared resource, you need a lock. In a single process, a mutex works fine. Across multiple servers, you need a distributed lock: a way for any process to claim exclusive access, do its work, and release the lock so others can proceed. Common use cases include preventing duplicate cron job execution, serializing access to external APIs with strict rate limits, and ensuring only one worker processes a specific task.

📄️ How to Build Feature Flags in Redis

Feature flags let you enable or disable functionality without deploying new code. They decouple releases from deployments: you can ship code to production with a feature turned off, then flip it on for specific users, a percentage of traffic, or everyone at once. This enables gradual rollouts, A/B testing, kill switches for problematic features, and beta access for specific customers.

📄️ How to Track Online Users in Redis

Knowing who is currently online powers features like "5 friends are active," green status dots in chat applications, and "3 people are viewing this document." The challenge is that "online" is fuzzy. Users do not explicitly log out. They close browser tabs, lose network connections, or just walk away. A presence system must infer status from activity and handle users who silently disappear.

📄️ How to Store User Sessions in Redis

Web applications need to remember who you are between requests. After you log in, the server creates a session) containing your user ID, permissions, and other state. Each subsequent request includes a session ID that the server uses to look up this data. The challenge is where to store sessions when you have multiple application servers behind a load balancer).