- A
The API Gateway stage is not redeployed after enabling CORS.
Why wrong: Redeploy is necessary but the symptom of CORS errors would be consistent; the most likely cause is missing headers from Lambda.
- B
The API Gateway CORS configuration is incorrect; the allowed origin should be set to '*'.
Why wrong: Wildcard may work but not the most secure; the issue is likely missing headers from Lambda.
- C
The web application is not sending the preflight OPTIONS request.
Why wrong: The browser automatically sends preflight; if CORS is configured, OPTIONS should be handled.
- D
The Lambda function is not returning the CORS headers in the response.
For non-proxy integrations, the Lambda must include CORS headers in its response.
Question 1,503 of 1,616
Troubleshooting CORS Errors: Lambda Must Return Headers
This DVA-C02 practice question tests your understanding of development with aws services. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 developer is building a REST API using Amazon API Gateway and AWS Lambda. The API must support CORS to allow requests from a web application hosted on a different domain. The developer has enabled CORS on the API Gateway resource and configured the Lambda function to return the appropriate headers. However, the web application is still receiving CORS errors. What is the most likely cause?
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 is not returning the CORS headers in the response.
Even though the developer enabled CORS on API Gateway, the Lambda function must also return the required CORS headers (Access-Control-Allow-Origin, etc.) in its HTTP response. API Gateway's CORS configuration only handles the preflight OPTIONS response; the actual response from the Lambda integration must include the headers for the browser to accept the cross-origin request. Without these headers in the Lambda response, the browser will reject the request, causing CORS errors.
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 API Gateway stage is not redeployed after enabling CORS.
Why it's wrong here
Redeploy is necessary but the symptom of CORS errors would be consistent; the most likely cause is missing headers from Lambda.
- ✗
The API Gateway CORS configuration is incorrect; the allowed origin should be set to '*'.
Why it's wrong here
Wildcard may work but not the most secure; the issue is likely missing headers from Lambda.
- ✗
The web application is not sending the preflight OPTIONS request.
Why it's wrong here
The browser automatically sends preflight; if CORS is configured, OPTIONS should be handled.
- ✓
The Lambda function is not returning the CORS headers in the response.
Why this is correct
For non-proxy integrations, the Lambda must include CORS headers in its response.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume enabling CORS on API Gateway automatically adds headers to all responses, but in reality, the Lambda function must explicitly include the CORS headers in its response payload.
Detailed technical explanation
How to think about this question
CORS is enforced by the browser, not the server. For a non-simple request (e.g., with custom headers or non-GET/POST methods), the browser sends a preflight OPTIONS request to check the server's CORS policy. API Gateway can be configured to return the appropriate CORS headers for the OPTIONS response, but the actual response from the Lambda integration must also include the Access-Control-Allow-Origin header. If the Lambda function omits this header, the browser will block the response even if the preflight succeeds. A common real-world scenario is when the Lambda function returns a 4xx or 5xx error without headers, causing CORS failures.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
- →
Development with AWS Services — study guide chapter
Learn the concepts, then practise the questions
- →
Development with AWS Services practice questions
Targeted practice on this topic area only
- →
All DVA-C02 questions
1,616 questions across all exam domains
- →
AWS Certified Developer Associate DVA-C02 study guide
Full concept coverage aligned to exam objectives
- →
DVA-C02 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related DVA-C02 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Development with AWS Services practice questions
Practise DVA-C02 questions linked to Development with AWS Services.
Security practice questions
Practise DVA-C02 questions linked to Security.
Deployment practice questions
Practise DVA-C02 questions linked to Deployment.
Troubleshooting and Optimization practice questions
Practise DVA-C02 questions linked to Troubleshooting and Optimization.
DVA-C02 fundamentals practice questions
Practise DVA-C02 questions linked to DVA-C02 fundamentals.
DVA-C02 scenario practice questions
Practise DVA-C02 questions linked to DVA-C02 scenario.
DVA-C02 troubleshooting practice questions
Practise DVA-C02 questions linked to DVA-C02 troubleshooting.
Practice this exam
Start a free DVA-C02 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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 is not returning the CORS headers in the response. — Even though the developer enabled CORS on API Gateway, the Lambda function must also return the required CORS headers (Access-Control-Allow-Origin, etc.) in its HTTP response. API Gateway's CORS configuration only handles the preflight OPTIONS response; the actual response from the Lambda integration must include the headers for the browser to accept the cross-origin request. Without these headers in the Lambda response, the browser will reject the request, causing CORS errors.
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 →
Keep practising
More DVA-C02 practice questions
- A developer is troubleshooting an AWS Lambda function that is triggered by an S3 event. The function occasionally fails…
- A developer needs to call AWS APIs from application code running on EC2. Which credential source should the AWS SDK use…
- A developer needs to allow an IAM user in a different AWS account to assume a role in the developer's account. The role…
- A developer needs to grant an IAM role in Account B read-only access to objects in an S3 bucket in Account A. The bucket…
- An API Gateway HTTP API should allow access only to users authenticated by an external OIDC provider. Which authorizer t…
- A developer needs to allow an EC2 instance to read from a DynamoDB table. Which is the best practice to grant permission…
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.