How would you design a distributed cache like Redis Cluster?
⚡ Short Answer
Partition keys across nodes with consistent hashing, replicate each shard (primary + replicas) for availability with automatic failover, and evict via LRU/LFU under memory pressure with TTLs. Handle hot keys (replication/local cache), cache stampedes (single-flight), and decide the consistency model (usually eventual).
☕Coffee Chat Question
Concept Made Simple
“How would you design a distributed cache like Redis Cluster?”
🧠Mind Map Answer
Remember It Faster
🔥What If?
Think Beyond the Expected
One key is so hot it overloads its shard's node — how do you handle it?
Replicate that hot key to multiple nodes and read from any (or add a small local/client-side cache in front), and use single-flight to prevent stampedes. Consistent hashing spreads keys, but a single super-hot key still needs replication or client-side caching to spread the read load.
😂Real World
Redis Cluster/Memcached designs combine consistent hashing, replication + failover, and eviction; the hard parts in interviews are hot keys, stampedes, and the consistency/availability trade-off.
🎯Interviewer's Expectation
Keywords they're listening for:
⚠️Common Mistakes
- ✗No hot-key strategy
- ✗No replication (cache node failure = thundering herd)
- ✗Ignoring eviction policy tuning
✅Best Practices
- ✓Consistent hashing + replication + failover
- ✓TTL + LRU/LFU; single-flight loads
- ✓Replicate/local-cache hot keys
🔁Follow-up Questions
- 1How does failover pick a new primary?
- 2LRU vs LFU eviction — when each?
- 3How do you keep the cache consistent with the DB?
🧩Related Technologies
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Plain-language foundations
I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner. Topic: Caching (System Design) Interview question: "How would you design a distributed cache like Redis Cluster?" Please: 1. Explain the core idea in simple, plain language, using an everyday analogy. 2. Define any technical terms you use. 3. Walk through one small, concrete example. 4. Finish with a single sentence I can easily remember. Keep the tone friendly and assume I'm new to this topic.
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