Private subnets across three AZs need resilient outbound internet access. What's the operationally sound design?
A.One NAT gateway shared by all AZs
If that AZ or gateway fails, all private subnets lose outbound — single point of failure.
B.One NAT gateway per AZ with route tables pointing each AZ's subnets to its local gateway
Correct. Per-AZ gateways + per-AZ routes = zonal isolation.
C.One NAT instance in a public subnet
NAT instances need manual failover and bandwidth management.
D.Give every instance a public IP
Public IPs defeat the purpose of private subnets.
Why this answer
A NAT gateway is zonal — a single gateway becomes an outage for every AZ routing through it. The resilient pattern: NAT gateway per AZ, each AZ's private subnets route to their local one. NAT instances are the legacy DIY version with scaling/failover burdens.
Correct answer: B · Last reviewed 2026-10-28
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