AdvancedScenario
15 min
SNAT Port Exhaustion via NAT Gateway
Cloud NetworkingNATScalability
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Interview Question
Outbound calls from your private subnets start failing intermittently. Investigation suggests SNAT port exhaustion. How do you confirm and fix?
Key Points to Cover
- Confirm via NAT gateway metrics (connections/ports in use)
- Correlate to bursty egress patterns and connection reuse
- Increase NAT gateways or scale subnets; tune timeouts
- Enable connection pooling/keep-alive and reduce parallel outbound
- Implement egress proxy or VPC endpoints for popular services
Evaluation Rubric
Confirms SNAT exhaustion with metrics35% weight
Optimizes client connection behavior25% weight
Scales NAT/egress capacity safely20% weight
Reduces reliance via endpoints/proxies20% weight
Hints
- 💡Ephemeral port reuse and TIME_WAIT tuning matter.
Potential Follow-up Questions
- ❓How to size NAT capacity?
- ❓What’s the impact of HTTP/2 multiplexing?
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