SAA-C03 Design High-Performing Architectures Practice Question
Exhibit
Benchmark summary from current fleet: - Current instances: c6i.2xlarge - Average CPU during processing: 88%-96% - Disk and network utilization remain below 30% - Application runtime on test ARM build: 11% faster than x86 build - Engineering note: binaries are already compatible with ARM64 - Business goal: lower cost while keeping or improving throughput
Based on the exhibit, a batch-processing service runs on Amazon EC2. The workload is Linux-based, can run on ARM64, and is CPU-bound during its nightly processing window. The team wants the best throughput per dollar without changing the application logic. Which EC2 instance family should the solutions architect recommend?
⚠ Common exam trap
Many exam-takers choose memory-optimized or general-purpose instances (like R7i or M7a) thinking they are safer, or burstable instances (T3) assuming they handle spikes cheaply, without recognizing that compute-optimized ARM64 instances (C7g) provide the best throughput per dollar for CPU-bound, ARM64-compatible workloads.
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
✓
C7g instances based on AWS Graviton processors
The C7g instances are based on AWS Graviton processors (ARM64 architecture), which offer up to 25% better performance per dollar compared to x86-based instances for CPU-bound workloads. Since the workload is Linux-based, can run on ARM64, and is CPU-bound, the C7g family provides the best throughput per dollar without requiring any application logic changes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
C7g instances based on AWS Graviton processors
Why this is correct
C7g instances are compute optimized and use Graviton processors, which often deliver strong price-performance for CPU-bound Linux workloads that can run on ARM64. The exhibit shows the application is compatible and even benchmarks faster on ARM.
- ✗
R7i instances because more memory will improve CPU-bound job throughput.
Why it's wrong here
R7i instances are memory-optimized, built with high-speed DDR5 memory and increased memory bandwidth, which benefits memory-caching or in-memory analytics workloads. However, your batch job is CPU-bound, meaning it is constrained by available compute cycles rather than by memory capacity or memory bandwidth. Adding more RAM does not directly reduce CPU execution time, and R7i's higher cost per vCPU will degrade your throughput-per-dollar for this purely compute-intensive workload.
- ✗
M7a instances because general-purpose families are always the safest performance choice.
Why it's wrong here
M7a instances are general-purpose AMD EPYC-based instances with a balanced vCPU-to-memory ratio, making them a reasonable default for unknown or mixed workloads, but not a principled choice for a clearly CPU-bound batch service. The phrase 'always the safest' is misleading because AWS instance selection should always match the specific workload bottleneck, not rely on a one-size-fits-all rule. Given the exhibit shows faster benchmarks on ARM64, choosing M7a surrenders the superior price-performance of C7g without adding any meaningful capability for this particular job.
- ✗
T3 instances because burstable instances can handle occasional nighttime spikes at lower cost.
Why it's wrong here
T3 instances are burstable, offering a modest baseline CPU utilization and accumulating CPU credits only when the instance is idle or underutilized. A sustained CPU-heavy batch service that runs near saturation will rapidly exhaust those credits, after which the instance is throttled to the baseline CPU level, causing a severe drop in batch throughput and inconsistent job completion times. While T3 is cost-effective for sporadic or low-average-CPU workloads, it cannot handle the continuous high CPU demand this batch service requires without either missing SLAs or incurring additional unlimited-mode charges.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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