SAA-C03 Design High-Performing Architectures Practice Question
A Lambda-based retail API has unpredictable traffic spikes and users see latency caused by cold starts. The function must respond consistently during expected campaign windows. What should be configured? The design must avoid adding custom operational scripts.
⚠ Common exam trap
Many candidates confuse reserved concurrency (which prevents throttling but does not address cold starts) with provisioned concurrency (which eliminates cold starts by keeping environments warm).
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
✓
Provisioned concurrency during campaign windows
Provisioned concurrency initializes a specified number of execution environments in advance, eliminating cold starts during campaign windows. This ensures consistent response times for the Lambda-based retail API under unpredictable traffic spikes without requiring custom scripts.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A larger deployment package
Why it's wrong here
A larger deployment package directly increases the time Lambda spends loading your code and dependencies during a cold start. Because cold-start latency is dominated by the need to download, unpack, and initialize your function bundle before the runtime is ready, bigger packages lengthen the delay rather than shorten it. Consequently, this option aggravates the response-time problem during unpredictable traffic spikes.
- ✗
Reserved concurrency only
Why it's wrong here
Reserved concurrency only sets a hard ceiling on how many instances of your function can run simultaneously and prevents other functions from occupying that capacity. It does not pre-create or initialize any execution environments, so the first request after a scaling event still incurs a cold-start delay as Lambda provisions a new sandbox. This makes reserved concurrency useful for protecting capacity, but it cannot reduce latency during unpredictable spikes because it leaves execution environments idle in the ON-DEMAND state until invoked.
- ✓
Provisioned concurrency during campaign windows
Why this is correct
Provisioned concurrency is the correct choice because it instructs Lambda to pre-initialize a specified number of execution environments before traffic arrives, eliminating cold-start latency for those warm instances. During known campaign windows, you can adjust the provisioned concurrency level to align with expected demand. This allows the retail API to serve requests instantly during a traffic surge instead of waiting for environment creation. You pay for the pre-warmed capacity even when idle, but it directly solves the stated low-latency requirement.
- ✗
CloudTrail data events
Why it's wrong here
CloudTrail data events record API activity, such as every Lambda function invocation, for audit and governance purposes. Enabling these events adds logging overhead and does not create any warm execution environments, so it has no effect on reducing cold-start latency. In fact, the extra logging can slightly increase the time per invocation, making this option counterproductive for improving response times during traffic spikes.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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