Redis is used for caching and sessions. When Redis times out, the entire application slows or crashes. Here's how to diagnose and resolve these problems.
Symptoms
- "Connection timed out" errors to Redis
- Response time that suddenly increases
- Lost sessions or ignored cache
- "Redis connection refused" errors
Common Causes
- Redis overloaded: Too many operations or blocking commands (KEYS *).
- Memory full: Redis reaches maxmemory and evicts or refuses writes.
- Unstable network: Network latency between app and Redis, especially on remote services.
Diagnostic Steps
- Test connectivity with redis-cli ping
- Check memory with INFO memory
- Analyze slow commands (SLOWLOG GET 10)
- Check connection count (INFO clients)
Automate with MoniTao
MoniTao detects Redis problem effects:
- Monitoring of application response times
- Alerts on sudden 500 errors
- Heartbeat for jobs using Redis
Best Practices
- Avoid KEYS * in production, use SCAN
- Configure maxmemory with an eviction policy
- Use an appropriate connection timeout
- Implement a fallback if Redis is unavailable
FAQ
What timeout to configure?
Connection: 2-5s. Command: depends on operation. Avoid 0 (infinite).
What if Redis is full?
Increase maxmemory or configure an eviction policy (allkeys-lru).
Sentinel or Cluster?
Sentinel for simple high availability. Cluster for horizontal scaling.
Can MoniTao monitor Redis directly?
No, but it monitors impact on your application (response times, errors).
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