What are all the ways my system can fail under real traffic?

Your system works perfectly in testing. Then real traffic arrives, latency spikes, database connections run out, retries multiply, and one struggling dependency brings down seemingly unrelated features.

Most production outages aren't caused by one dramatic bug. They happen because ordinary failure modes combine under real concurrency, real network conditions, and unpredictable user behavior.

What You'll Learn

• How overload, queue buildup, and resource exhaustion trigger outages.
• Why retries, slow dependencies, and shared resources cause cascading failures.
• How database bottlenecks, stale reads, and race conditions corrupt behavior.
• How network failures, third-party outages, and bad deployments affect availability.
• Why observability gaps and operational mistakes increase incident duration.
• How to turn a failure-mode checklist into a practical reliability-testing plan.

13 Categories of Production Failure

1. Capacity and overload failures
2. Resource exhaustion
3. Cascading and propagating failures
4. Database and data-layer failures
5. Network and infrastructure failures
6. Concurrency and race conditions
7. Dependency and third-party failures
8. Deployment and rollout failures
9. Client and input-driven failures
10. Data consistency and correctness failures
11. Observability and detection failures
12. Human and process failures
13. Scale-triggered failures that don't appear at low volume

How to Use the Checklist

Review every category against your own architecture. Mark each failure mode as handled, partially handled, or unknown. For every unknown, identify the test, metric, alert, or recovery mechanism needed to close the gap.

Prioritize failures by their likelihood and blast radius, not just by how dramatic they sound. Revisit the checklist after incidents to incorporate what production has taught you.

Key Takeaway

Reliability isn't about eliminating every possible failure. It's about making failures predictable, contained, observable, and recoverable.

Before calling a system production-ready, ask: Have we actually tested these failure modes, or have we simply assumed our system can handle them?