SAA-C03 Design Cost-Optimized Architectures Practice Question
A batch analytics job currently uses two NAT gateways in each of three Availability Zones, but only one private subnet per AZ needs outbound internet access. What should the architect review first? The architecture review board prefers a managed AWS-native control.
⚠ Common exam trap
A common mix-up: candidates assume more NAT gateways automatically mean better availability or performance, overlooking that a single NAT gateway per AZ is often sufficient and that cost optimization should be the first review priority when multiple gateways are deployed per AZ.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Whether one NAT gateway per AZ is sufficient for the required private subnets
The architecture currently uses two NAT gateways per AZ, but only one private subnet per AZ requires outbound internet access. Since a single NAT gateway in an AZ can serve all private subnets in that AZ via the route table, the first step is to verify whether one NAT gateway per AZ is sufficient for the required throughput and availability. This aligns with cost optimization by eliminating unnecessary NAT gateway hourly charges and data processing fees.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Replacing every NAT gateway with an internet gateway attached to private subnets
Why it's wrong here
An internet gateway is a VPC-level component that only provides direct internet access to instances with public IP addresses and a route table entry targeting the IGW; it does not perform source NAT for private instances. Private subnets have no public IPs, so replacing NAT gateways with IGWs would neither route outbound traffic nor support return traffic. IGWs are also free, but requiring public IPs destroys the private subnet boundary and is not a like-for-like replacement.
- ✓
Whether one NAT gateway per AZ is sufficient for the required private subnets
Why this is correct
NAT gateways are zonal resources, and AWS best practice is to deploy one per Availability Zone for high availability; multiple NAT gateways in the same AZ offer no added resilience because an AZ failure takes them all down. Before optimizing cost, verify whether each private subnet in each AZ actually needs outbound NAT capacity. If batch workloads run primarily in one AZ or can tolerate reduced availability, a single NAT gateway may be sufficient, but cross-AZ traffic from other AZs will incur inter-AZ data transfer charges in addition to the NAT gateway hourly and per-GB processing costs.
- ✗
Disabling route tables
Why it's wrong here
Route tables are mandatory for all subnets; every subnet must be associated with a route table, and each route table must contain at least the local VPC route to allow internal communication. There is no supported operation to 'disable' a route table, and doing so would cause all traffic in the affected subnets to fail, including the VPC-internal traffic required by the batch analytics job. This is not a valid cost-optimization action and would break networking entirely.
- ✗
Moving all workloads to public subnets
Why it's wrong here
Moving batch workloads to public subnets would require assigning public IP addresses and adding internet gateway routes, exposing the instances to inbound internet traffic and significantly increasing the attack surface. Security groups and network ACLs would need major redesign, and the private-subnet architecture that supports outbound-only internet access would be lost. Eliminating NAT gateway costs by placing workloads in public subnets is a security anti-pattern, not a cost-first best practice, and it fundamentally changes the system's networking model.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.