- A
The DynamoDB table has insufficient write capacity.
Why wrong: DynamoDB throttling returns a 400 error, not 503.
- B
The Lambda function execution time exceeds the configured timeout.
Lambda timeout causes API Gateway to return a 503.
- C
The Lambda function's IAM role does not have permission to write to DynamoDB.
Why wrong: Missing permissions cause a 500 or 403, not 503.
- D
The API Gateway stage has throttling limits configured.
Why wrong: Throttling returns 429, not 503.
Question 475 of 1,616
Lambda Function Timeout Causing API Gateway 503 Errors
This DVA-C02 practice question tests your understanding of development with aws services. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is building a serverless application using AWS Lambda functions that write results to an Amazon DynamoDB table. The Lambda functions are invoked by an Amazon API Gateway REST API. During testing, some requests fail with a 503 status code. The Lambda function code is correct. What is the MOST likely cause of the 503 errors?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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 execution time exceeds the configured timeout.
The 503 status code from API Gateway typically indicates a service unavailable error, which in this context is most likely caused by the Lambda function timing out before it can complete its execution. When the Lambda function's execution time exceeds the configured timeout (default 3 seconds, max 15 minutes), API Gateway receives no response and returns a 503 error. Since the code is correct and the issue occurs during testing, a timeout is the most plausible cause, as it directly leads to API Gateway's integration timeout.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 DynamoDB table has insufficient write capacity.
Why it's wrong here
DynamoDB throttling returns a 400 error, not 503.
- ✓
The Lambda function execution time exceeds the configured timeout.
Why this is correct
Lambda timeout causes API Gateway to return a 503.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The Lambda function's IAM role does not have permission to write to DynamoDB.
Why it's wrong here
Missing permissions cause a 500 or 403, not 503.
- ✗
The API Gateway stage has throttling limits configured.
Why it's wrong here
Throttling returns 429, not 503.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 503 errors with throttling (429) or permission issues (500), but the 503 specifically points to a timeout or service unavailability from the Lambda integration, not from DynamoDB or API Gateway throttling.
Detailed technical explanation
How to think about this question
API Gateway has a maximum integration timeout of 29 seconds for Lambda integrations; if the Lambda function exceeds this, API Gateway terminates the connection and returns a 503. Under the hood, API Gateway uses a synchronous invocation of Lambda, and the Lambda service returns a 503 if the function times out or the invocation request is throttled. In real-world scenarios, cold starts or heavy computation can push execution time beyond the configured timeout, especially if the timeout is set too low (e.g., 3 seconds) for the workload.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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 |
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this DVA-C02 question test?
Development with AWS Services — This question tests Development with AWS Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Lambda function execution time exceeds the configured timeout. — The 503 status code from API Gateway typically indicates a service unavailable error, which in this context is most likely caused by the Lambda function timing out before it can complete its execution. When the Lambda function's execution time exceeds the configured timeout (default 3 seconds, max 15 minutes), API Gateway receives no response and returns a 503 error. Since the code is correct and the issue occurs during testing, a timeout is the most plausible cause, as it directly leads to API Gateway's integration timeout.
What should I do if I get this DVA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more ways this is tested on DVA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A developer is deploying a Node.js application on AWS Lambda. The function uses the 'axios' library to call an external API. After deployment, the function times out after 3 seconds. The external API response time is normally under 500 ms. What should the developer do to resolve this issue?
hard- ✓ A.Increase the Lambda function timeout to 10 seconds.
- B.Increase the Lambda function reserved concurrency.
- C.Remove the Lambda function from the VPC.
- D.Increase the Lambda function memory to 1024 MB.
Why A: The Lambda function is timing out because the default timeout is 3 seconds, and the external API call via the 'axios' library is taking longer than that, even though the API normally responds within 500 ms. The most direct fix is to increase the Lambda function timeout to 10 seconds to accommodate any transient delays or cold-start overhead that may cause the API call to exceed 3 seconds. This ensures the function has enough time to wait for the HTTP response without failing.
Keep practising
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Last reviewed: Jul 4, 2026
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.
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