Compute purchasing options: CLF-C02 study notes and practice questions
What to know about Compute purchasing options for the CLF-C02 exam, from the Billing, Pricing, and Support domain (12% of the exam guide), then 2 free questions to test it. Part of the CLF-C02 study guide.
Pricing model questions describe how a workload runs (steady, short-term, interruptible, licensed per core) and ask for the cheapest suitable way to pay for it.
The options
Option
How it works
Best for
On-Demand
Pay by the second or hour, no commitment
Short-term, unpredictable or new workloads
Savings Plans
Commit to a dollar amount per hour for 1 or 3 years, for up to 72% off
Steady use; Compute Savings Plans also cover Fargate and Lambda and any instance family or Region
Reserved Instances
Commit to an instance type in a Region for 1 or 3 years, for up to 72% off
Steady use of a specific instance type; Convertible RIs can be exchanged for other types
Spot Instances
Use spare capacity for up to 90% off; AWS can reclaim it with a 2-minute warning
Flexible, interruptible work: batch jobs, testing, data analysis
Dedicated Hosts
A whole physical server for you
Licenses tied to sockets or cores, compliance needs
Dedicated Instances
Instances on hardware not shared with other customers
Isolation without host-level control
Capacity Reservations
Reserve capacity in a specific Availability Zone, billed whether used or not, no term
Guaranteeing capacity for a known event
Payment options for commitments
All Upfront gives the biggest discount, Partial Upfront less, No Upfront the least. A 3-year term saves more than a 1-year term.
How to choose
“Runs 24/7 for the next three years”: Savings Plan or Reserved Instances.
“Can stop and restart at any time without harm”: Spot.
“A two-week project”: On-Demand.
“Software licensed per physical core”: Dedicated Hosts.
“Need guaranteed capacity in one AZ next month, no long commitment”: On-Demand Capacity Reservation.
Common traps
Spot for a production database. It can be interrupted.
Reserved Instances for a short project. The commitment is 1 or 3 years.
Dedicated Instances for per-core licensing. Only Dedicated Hosts show the physical cores.
D. Wrong: This combines Standard terms with a single Availability Zone. Standard Reserved Instances cannot be exchanged, so the family change would not be covered.
Explanation
Convertible Reserved Instances trade a little of the discount for flexibility, because they can be exchanged for another instance family during the term. Standard Reserved Instances cannot be exchanged, and Spot Instances carry no commitment at all.
A company must be sure it can launch 20 Amazon EC2 instances of one type in a single Availability Zone for a planned two-week event.
It does not want a one-year or three-year commitment, and having the capacity guaranteed matters more than a discount.
Which option should it use?
Choose one answer.
AA. On-Demand Capacity Reservations in that zone
BB. Spot Instances booked for that Availability Zone
CC. Compute Savings Plans for the two-week event period
DD. Regional Reserved Instances for the whole Region
Show the answer and explanation
Answer: A
A. Right: Capacity Reservations reserve EC2 capacity in a specific Availability Zone with no commitment term. The company pays while the reservation is active, and it cancels when the event ends. Learn more: Capacity Reservations (opens in a new tab)
B. Wrong: Spot capacity is spare, and AWS can reclaim it at short notice. It cannot guarantee that all 20 instances launch.
C. Wrong: Savings Plans require a one- or three-year commitment to an hourly spend, and they do not reserve capacity in any zone.
Capacity Reservations are the only option that guarantees capacity in a chosen Availability Zone without a one- or three-year term. Spot can be reclaimed, Savings Plans and Regional Reserved Instances give discounts on usage rather than reserved capacity, and they need a term commitment.
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