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SOA-C03 practice question: Network cost optimization

Networking and Content Delivery A free question from our original SOA-C03 practice exam. Try it, then open the answer to see why each option is right or wrong.

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A regional bank's statement-generation instances run in private subnets and write about 40 TB a month to Amazon S3 buckets in the same Region through a NAT gateway.

The monthly bill shows high NAT gateway data processing charges.

Security policy requires that this traffic stay off the public internet.

What should a CloudOps engineer do to reduce the cost while meeting the policy?

Choose one answer.

  1. A. Replace the NAT gateway with a NAT instance on a large EC2 instance type to avoid per-gigabyte processing charges.
  2. B. Turn on S3 Transfer Acceleration so that the uploads use the AWS edge network instead of the NAT gateway.
  3. C. Create an S3 gateway VPC endpoint and add it to the route tables of the private subnets.
  4. D. Move the NAT gateway to the same Availability Zone as most of the instances to remove the processing charges.
Show the answer and explanation

Answer: C

Explanation

NAT gateways charge for each gigabyte they process, which grows quickly for bulk S3 traffic. A gateway VPC endpoint for S3 is free and keeps traffic on the AWS network, so moving S3 traffic onto it removes most of the charge. Interface endpoints for S3 also exist but have hourly and per-gigabyte charges.

A gateway VPC endpoint for S3 or DynamoDB beside a NAT gateway An application in a private subnet uses a route table. Traffic for the S3 or DynamoDB prefix list goes to a gateway endpoint, which is free and can carry an endpoint policy, and reaches the service over the AWS network. Any other internet traffic still goes through a NAT gateway. Private subnets Application private subnet Route table prefix list → endpoint Gateway endpoint free, endpoint policy NAT gateway other traffic only S3 or DynamoDB AWS network Internet
S3 traffic follows the endpoint route instead of the NAT gateway, so the per-gigabyte NAT charge goes away.

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