SOA-C02 Cost and Performance Optimization Practice Question
A company runs a batch processing job on Amazon EC2 that runs for 2 hours every night. The job can tolerate interruptions and can resume from the last checkpoint. The SysOps administrator needs to minimize compute costs. Which EC2 purchasing option should be used?
⚠ Common exam trap
Watch out — candidates often choose Reserved Instances or Savings Plans because they assume any long-running workload needs a commitment, but the question explicitly states the job is interruptible and runs only 2 hours nightly, making Spot Instances the correct cost-optimization choice.
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
✓
Spot Instances
Spot Instances are ideal for fault-tolerant, interruptible workloads like this batch processing job because they offer significant cost savings (up to 90% off On-Demand prices) in exchange for being reclaimable by AWS with a 2-minute warning. Since the job can resume from the last checkpoint, interruptions do not cause data loss or restart from scratch, making Spot Instances the most cost-effective choice.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
On-Demand Instances
Why it's wrong here
On-Demand Instances incur the full hourly rate per second with no upfront payment and no volume discount, and they are guaranteed not to be reclaimed unexpectedly. For a workload that runs only a short nightly batch and can tolerate interruptions, choosing On-Demand means paying the highest possible price for every compute hour. Since Spot can handle the same job at up to a 90% discount, On-Demand is a poor cost decision despite its operational simplicity.
- ✓
Spot Instances
Why this is correct
Spot Instances provide access to spare AWS compute capacity at discounts of up to 90% versus On-Demand, but AWS can reclaim them with only a two-minute warning. Batch processing jobs with checkpointing are a canonical Spot use case because a reclaimed instance creates no data loss and the work can simply be retried. Using Spot Fleet or EC2 Fleet with multiple instance types and Availability Zones increases resilience and maintains throughput during interruptions, making Spot the optimal and lowest-cost choice.
- ✗
Reserved Instances
Why it's wrong here
Reserved Instances require a 1- or 3-year payment commitment in exchange for a lower effective hourly price, and they are designed for steady-state workloads that run continuously. A nightly batch job runs for a small fraction of the day, so the reserved capacity would sit idle for most of the billing period, erasing the savings. Additionally, Standard RIs are inflexible to changes in instance family or region, while a batch job may need to vary instance types. Thus, RIs do not fit the short, non-continuous nature of this workload.
- ✗
Compute Savings Plans
Why it's wrong here
Compute Savings Plans provide a discount over On-Demand in exchange for committing to a fixed hourly dollar amount for one or three years, but you must pay for that commitment even when the EC2 instances are not running. Since the batch job is active only for a short nightly window, the plan would cover many idle hours, making it cost-inefficient. Also, Savings Plans do not apply to Spot Instances, so they cannot reach the same low price point that Spot offers. The workload's interruptibility and short duration favor Spot, not a long-term savings commitment.
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Same concept, more angles
4 more ways this is tested on SOA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company runs a CPU-intensive batch processing job daily on a single Amazon EC2 instance. The job requires high compute performance but uses minimal memory. The instance is typically idle for the rest of the day. The SysOps administrator needs to minimize costs while ensuring the job completes within a 1-hour window. Which purchasing option and instance family should the administrator use?
easy- A.On-Demand Instance with a general-purpose (T-family) instance
- ✓ B.Reserved Instance (1-year, all upfront) with a compute-optimized (C-family) instance
- C.Spot Instance with a compute-optimized (C-family) instance
- D.On-Demand Instance with a memory-optimized (R-family) instance
Why B: A Reserved Instance with a compute-optimized (C-family) instance is the appropriate choice because the job requires high CPU performance and must complete reliably within a 1-hour window. Spot Instances are subject to interruption and cannot guarantee completion, especially for a single-instance batch job. While Reserved Instances involve a 1-year commitment, this option ensures the instance is available when needed, and the compute-optimized family matches the CPU-intensive profile. On-Demand instances would be cheaper for low utilization, but that option is not available with a compute-optimized family in the given choices.
Variation 2. A company runs a batch processing job every night on Amazon EC2 instances. The job takes exactly 2 hours to complete and can be interrupted and resumed later. The SysOps administrator wants to minimize compute costs. Which purchasing option should be used?
medium- ✓ A.Spot Instances
- B.Reserved Instances
- C.On-Demand Instances
- D.Dedicated Instances
Why A: Spot Instances are the correct choice because the batch job is fault-tolerant (can be interrupted and resumed) and runs for a fixed 2-hour window nightly. Spot Instances offer up to 90% cost savings compared to On-Demand, and with the ability to handle interruptions via checkpointing, they minimize compute costs without requiring a long-term commitment.
Variation 3. A company runs a batch processing job on Amazon EMR every night. The job runs for 6 hours and requires a cluster of 20 m5.xlarge instances. The company wants to reduce costs while ensuring the job completes on time. Which solution is MOST cost-effective?
medium- A.Use On-Demand instances for all nodes.
- B.Purchase Reserved Instances for the entire cluster.
- ✓ C.Use Spot Instances for core and task nodes and an On-Demand instance for the primary node.
- D.Use Spot Instances for the primary node and On-Demand for core and task nodes.
Why C: Amazon EMR clusters consist of a primary node (master), core nodes (which run HDFS and task processes), and task nodes (which only run tasks and can be lost without data loss). Spot Instances are ideal for task nodes because they can be interrupted without affecting HDFS data, and for core nodes if the cluster is resilient to interruptions (e.g., using EMRFS consistent view or if the job can tolerate some core node loss). The primary node must be On-Demand to avoid cluster termination if the Spot Instance is reclaimed. This mix minimizes cost while ensuring the job completes on time.
Variation 4. A company runs a batch processing job on Amazon EC2 instances that runs for 3 hours each night. The job can be interrupted and can resume from the last checkpoint without data loss. The SysOps administrator wants to minimize compute costs for this workload. Which Amazon EC2 purchasing option should be used?
easy- A.On-Demand Instances
- B.Reserved Instances
- ✓ C.Spot Instances
- D.Dedicated Hosts
Why C: Spot Instances are correct because the batch job is fault-tolerant (can be interrupted and resume from checkpoints) and runs for a fixed 3-hour window nightly. Spot Instances offer significant cost savings (up to 90% off On-Demand) by using spare EC2 capacity, which can be reclaimed by AWS with a 2-minute interruption notice. Since the workload can handle interruptions gracefully, Spot Instances minimize compute costs while meeting the job's requirements.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SOA-C02 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 SOA-C02 exam.