Private subnets in 3 AZs all route outbound through a single NAT gateway in AZ-a. An AZ-a outage breaks internet access for the other two. What's the resilient design?
A.One NAT gateway per AZ, each private subnet routes to its local NAT
Per-AZ NAT = the resilient pattern. Correct.
B.Bigger NAT gateway instance
NAT gateways scale bandwidth automatically — sizing isn't the issue, locality is.
C.NAT instances instead of managed NAT
NAT instances are older/manual — worse HA than managed NAT.
D.A second IGW for failover
IGWs are regional — not the bottleneck here.
Why this answer
NAT gateways are zonal — a single NAT is an AZ-level single point of failure. Best practice: one NAT per AZ and per-AZ route tables pointing at the local NAT. It's costlier (3 NATs) but removes the dependency.
Correct answer: A · Last reviewed 2026-11-05
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