Recently, I ran into a production issue that looked small at first… but ended up impacting a critical feature.
This is something many developers overlook when using Redis.
🧠 The Setup
I was using Redis for:
- Caching API responses
- Rate limiting requests
Everything was working perfectly in the beginning.
❌ The Problem
I did NOT configure any eviction policy.
As traffic increased:
- Redis memory got full
- New keys stopped getting stored
- Some APIs started failing
- Rate limiter stopped working properly
The worst part?
There was no obvious error initially — things just started behaving incorrectly.
🔍 Root Cause
By default, if Redis reaches its memory limit ("maxmemory") and no proper eviction policy is configured:
👉 Redis starts rejecting new write operations.
This caused:
- Cache failures
- Broken rate limiting logic
- Unexpected system behavior
🛠️ The Fix
I updated Redis configuration:
maxmemory 256mb
maxmemory-policy allkeys-lru
Why "allkeys-lru"?
- Removes least recently used keys
- Works best for caching systems
- Keeps frequently accessed data available
📈 Result
After applying the fix:
- System stabilized
- No more silent failures
- Rate limiter started working correctly
- Cache behaved as expected
💡 Key Learnings
If you're using Redis in production:
✅ Always do this:
- Set "maxmemory"
- Define an eviction policy
📌 Choose wisely:
- "allkeys-lru" → best for caching
- "volatile-ttl" → for expiry-based keys
- "noeviction" → risky unless handled explicitly
🔥 Final Thought
Never rely on default configurations for production systems.
Small misconfigurations in infrastructure can break entire systems silently.
🙌 Closing
This was a small mistake, but a big learning.
If you're building scalable backend systems, Redis configuration is just as important as your application logic.
Top comments (1)
this kind of issue is always annoying to track down
from the outside everything looks fine, then something like memory pressure changes behavior completely
no clear errors, just things slowly breaking
feels like a lot of these problems only show up once the system is under real load
you don’t really see it until production starts drifting