SOA-C02 Cost and Performance Optimization Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✓

  Use a mixed instances policy and set the 'On-Demand Base' capacity to the minimum number of instances required during business hours, and 'On-Demand percentage above base' to 0% so that any additional capacity is Spot.

  Why this is correct

  A mixed instances policy lets the Auto Scaling group combine On-Demand and Spot capacity while distributing across instance types. Setting On-Demand Base to the minimum needed during business hours creates a hardened floor that will always be fulfilled by On-Demand instances, and setting On-Demand percentage above base to 0% directs all growth beyond that floor to Spot Instances. This isolates the availability-critical baseline from Spot interruptions while saving money on the burst capacity, and it automatically balances between the two markets as the group scales in and out.

• ✗

  Use a launch template that specifies a Spot Instance type and set the total capacity to the desired level, relying on capacity rebalance to replace interrupted Spot Instances.

  Why it's wrong here

  This approach makes the entire Auto Scaling group Spot-only, so there is no guaranteed capacity floor. Capacity rebalance notices help the group proactively replace instances that EC2 predicts will be reclaimed, but the replacement instances are themselves Spot launches that can fail due to insufficient Spot capacity during periods of high demand. Relying on rebalance does not protect against a simultaneous wave of interruptions, and it still cannot ensure the minimum business-hour instance count remains running.

• ✗

  Purchase Compute Savings Plans to cover the entire Auto Scaling group, and use only Spot Instances for all capacity.

  Why it's wrong here

  Compute Savings Plans are a pricing agreement that lowers the hourly bill for consistent usage, but they are not a reservation of physical capacity and do nothing to keep Spot Instances from being reclaimed. If all required instances are Spot, any one of them can be interrupted at any time, so the group can drop below the minimum despite the savings plan being in effect. Savings Plans cover usage, not availability; combining them with an On-Demand base would be cost-effective, but using them as the only mitigation does not meet the requirement.

• ✗

  Configure the Auto Scaling group with a launch template that sets the instance market to 'spot' and use a scaling policy that always maintains the minimum capacity.

  Why it's wrong here

  Setting the launch template market to 'spot' and trusting a scaling policy to maintain minimum capacity mistakes reactive scaling for capacity assurance. Even if a scaling policy or the group's minimum tries to replace a terminated Spot Instance, a new Spot request can remain pending when EC2 lacks spare capacity in the configured Availability Zones, causing the group to operate below minimum for an extended period. The policy only adjusts the desired count; it cannot override Spot capacity constraints, and with no On-Demand fallback the baseline availability requirement is not guaranteed.

Go deeper

Related to this question