DVA-C02 Development with AWS Services Practice Question
A company is using AWS Lambda to process messages from an Amazon SQS queue. The Lambda function is configured with a reserved concurrency of 10. The SQS queue receives a burst of 1000 messages. The Lambda function processes each message in about 5 seconds. What is the most likely behavior of the system?
⚠ Common exam trap
Test-takers frequently assume Lambda automatically scales to handle any burst, but reserved concurrency explicitly limits scaling, and the exam tests understanding that this limit is enforced regardless of queue depth.
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
✓
Lambda processes up to 10 messages concurrently, and the rest remain in the queue until processing capacity is available.
Lambda's reserved concurrency of 10 caps the maximum number of concurrent executions. When the SQS queue receives 1000 messages, Lambda polls the queue and invokes the function with up to 10 messages at a time (based on batch size, default 1). The remaining messages stay in the queue and are retried after the visibility timeout expires, as Lambda processes messages in batches limited by the reserved concurrency.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Lambda rejects the messages and sends them to the dead-letter queue.
Why it's wrong here
When a Lambda function connected to an SQS queue has insufficient concurrency, messages are not immediately rejected or sent to a Dead-Letter Queue (DLQ). Instead, they remain in the source SQS queue. A message is only sent to a DLQ if the Lambda function fails to process it after a configured number of retries (determined by the maxReceiveCount on the source queue's redrive policy) or if the function's execution times out, not simply due to concurrency limits.
- ✗
Lambda automatically scales up to 1000 concurrent executions to process all messages quickly.
Why it's wrong here
AWS Lambda's automatic scaling for SQS event sources is constrained by any configured concurrency limits. In this scenario, a reserved concurrency of 10 explicitly caps the maximum number of concurrent function invocations at 10. Therefore, Lambda cannot scale up to 1000 concurrent executions, regardless of the message backlog, as it must respect the user-defined reserved concurrency setting.
- ✗
Lambda increases the reserved concurrency to accommodate the burst.
Why it's wrong here
Reserved concurrency is a user-defined configuration that allocates a specific number of concurrent executions to a particular Lambda function, preventing it from exceeding that limit. This setting is static and does not dynamically adjust based on incoming message volume or burst events. Lambda itself will never automatically increase or decrease a function's reserved concurrency; it must be manually modified by an administrator or through infrastructure-as-code.
- ✓
Lambda processes up to 10 messages concurrently, and the rest remain in the queue until processing capacity is available.
Why this is correct
When a Lambda function has a reserved concurrency of 10, it means that at any given moment, a maximum of 10 instances of that function can be executing simultaneously. If there's a sudden influx of messages from the SQS queue, Lambda will invoke up to 10 functions to process them. Any additional messages beyond what these 10 concurrent invocations can handle will remain in the SQS queue, awaiting an available function instance to process them.
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DVA-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 DVA-C02 exam.