Design Cost-Optimized Architectures

Getting Data In, and What It Costs

Migration questions usually hide a bandwidth calculation. Work out whether the data can physically cross the link in the time available before choosing a tool.

Exam tip. Do the bandwidth arithmetic first. It eliminates two or three answers on almost every migration question before you consider anything else.

Matching the Pricing Model to the Usage Shape

Every cost question is really asking you to recognise a usage shape. Get the shape right and the pricing model follows without any arithmetic.

Exam tip. Right-size before committing. A reservation on an oversized instance locks in the waste for the whole term.

How to Run a Cost Review Without Breaking Anything

Cost questions reward a specific order of operations. Doing the steps out of order either locks in waste or trades away reliability for money.

Exam tip. The exam's cost-optimised answer includes operational effort. A managed service at a higher hourly rate can still be the cheaper answer.

1. A workload runs 24 hours a day for at least the next three years on a predictable instance family. Which purchasing option gives the lowest cost?

• A. Dedicated Hosts billed on demand
• B. A three-year Compute Savings Plan or Reserved Instance commitmentcorrect
• C. On-Demand instances
• D. Spot Instances

A long-term commitment gives the deepest discount for steady, predictable usage. On-Demand is the most expensive per hour for constant load, Spot can be interrupted so it does not suit a service that must always run, and Dedicated Hosts cost more and are chosen for licensing or compliance reasons.

2. A company transfers 50 TB per month from AWS to its own datacentre and wants to reduce the cost of that egress. Which option is most likely to help?

• A. Move the data to Glacier before transferring it
• B. Use a NAT gateway for the outbound traffic
• C. Use AWS Direct Connect, which carries lower data transfer out rates than internet egresscorrect
• D. Enable S3 Transfer Acceleration for the transfers

Direct Connect data transfer out is priced below standard internet egress and becomes cost-effective at sustained high volume. Transfer Acceleration adds a premium, archiving adds retrieval cost, and a NAT gateway adds processing charges without reducing egress rates.