SAA-C03 Design High-Performing Architectures Practice Question
A serverless checkout API runs on AWS Lambda behind API Gateway. Traffic spikes are predictable every weekday at 09:00 UTC, and p95 latency jumps for the first few minutes after each deployment because execution environments are cold. The team wants to reduce this startup impact without changing the API contract. Which changes should they make? Select three.
⚠ Common exam trap
Test-takers frequently confuse reserved concurrency (which only limits concurrency) with provisioned concurrency (which pre-warms instances), leading candidates to incorrectly select reserved concurrency as a solution for cold starts.
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
✓
Configure provisioned concurrency on the production Lambda alias during the busy windows.
Provisioned concurrency initializes a specified number of execution environments in advance, so when traffic spikes at 09:00 UTC, the Lambda function is already warm and can serve requests without cold start latency. This directly addresses the p95 latency jump after deployment without altering the API contract.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure provisioned concurrency on the production Lambda alias during the busy windows.
Why this is correct
Correct. Provisioned concurrency keeps a pool of pre-initialized execution environments ready to handle invocations, which directly reduces cold-start latency. Using an alias allows the team to manage production traffic separately from development or canary versions and to schedule capacity for the predictable weekday peak.
- ✓
Initialize SDK clients and other reusable objects outside the handler so they are created once per execution environment.
Why this is correct
Correct. Code that runs outside the handler executes during environment initialization and is then reused for subsequent invocations in the same execution environment. Reusing database clients, SDK clients, connection pools, and compiled configuration reduces per-invocation setup time and lowers the first-request penalty.
- ✓
Reduce the deployment package size and remove unnecessary layers to shorten function initialization.
Why this is correct
Correct. Smaller packages and fewer dependencies generally reduce code download, unzip, and runtime initialization overhead. Trimming unused libraries and layers reduces the work required when Lambda creates a new execution environment after deployment or scale-out.
- ✗
Replace provisioned concurrency with reserved concurrency because reserved concurrency keeps instances warm.
Why it's wrong here
Incorrect. Reserved concurrency only sets an upper limit and optionally reserves capacity for a function; it does not pre-warm execution environments. Provisioned concurrency is the feature that initializes environments in advance to reduce cold starts.
- ✗
Increase the function timeout so the first request has more time to warm up.
Why it's wrong here
Incorrect. Timeout changes how long Lambda waits before it fails an invocation, but it does not reduce initialization time or improve the p95 latency experienced by the caller. The issue is startup overhead, not insufficient execution time.
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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