DVA-C02 Development with AWS Services Practice Question
A company is using AWS Lambda functions to process events from Amazon S3. The functions are writing logs to CloudWatch Logs. Recently, they noticed that some logs are missing and the functions are experiencing throttling errors. What is the MOST likely cause?
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
✓
The Lambda function's reserved concurrency is set to a low value.
The most likely cause of throttling errors is that the Lambda function's reserved concurrency is set too low. When a Lambda function's reserved concurrency limit is reached, additional invocation requests are throttled, resulting in missing logs. Option A is incorrect because log group retention affects log storage, not Lambda throttling. Option C is incorrect because IAM permissions affect the ability to write logs, not throttling. Option D is incorrect because while S3 can send many events, Lambda's concurrency limit is the direct cause of throttling.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The CloudWatch Logs log group retention policy is set too low.
Why it's wrong here
A low CloudWatch Logs log group retention policy dictates how long logs are stored before being automatically deleted. This setting solely impacts the availability of historical execution logs for auditing or debugging purposes. It has no direct bearing on the real-time execution capacity or concurrency limits of a Lambda function, and therefore cannot cause the function to be throttled. Throttling occurs when execution requests exceed available capacity, not due to log storage duration.
- ✓
The Lambda function's reserved concurrency is set to a low value.
Why this is correct
Reserved concurrency explicitly caps the maximum number of simultaneous executions for a specific Lambda function. When the rate of incoming events or requests attempts to invoke the function beyond this configured limit, subsequent invocation requests are immediately throttled. This mechanism ensures that the function does not consume more concurrency than allocated, preventing it from impacting other functions or exceeding account-level limits, directly resulting in throttling errors for excess requests.
- ✗
The Lambda function's IAM role lacks permissions to write to CloudWatch Logs.
Why it's wrong here
If the Lambda function's IAM execution role lacks the necessary permissions to write logs to CloudWatch Logs, the function would likely execute but fail to record its output or errors in CloudWatch. This would manifest as permission denied errors in the function's execution environment or invocation logs, not as throttling. Throttling specifically indicates that the service is refusing new invocations due to capacity limits, not a failure in an already-running invocation's logging capability.
- ✗
The S3 bucket is sending too many event notifications.
Why it's wrong here
S3 event notifications are delivered to Lambda asynchronously, meaning S3 does not wait for Lambda to process each event before sending the next. While a high volume of S3 events can certainly trigger a large number of Lambda invocations, S3 itself does not directly throttle the Lambda function. Instead, if the rate of S3 events causes Lambda's invocation requests to exceed the function's available concurrency (either reserved or unreserved), then Lambda's internal throttling mechanisms would activate, not S3's.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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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.