Request and response mapping in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

How does AWS API Gateway transform a request with mapping templates?

You have an AWS API Gateway method with a request mapping template that extracts the 'userId' from the incoming JSON body and passes it as a path parameter to the backend. What will be the value of the path parameter 'userId' if the incoming request body is {"userId": "12345", "action": "login"}?

AWS

{
  "userId": "$input.path('$.userId')"
}

A The path parameter 'userId' will be set to '12345'.

B The path parameter 'userId' will be set to 'action'.

C The path parameter 'userId' will be empty because the mapping template is invalid.

D The path parameter 'userId' will be set to '{"userId": "12345", "action": "login"}'.

💡 Hint

Think about how JSON path expressions extract values from the input JSON.

The mapping template uses $input.path('$.userId') which extracts the value of the 'userId' key from the JSON body. Since the input JSON has 'userId' set to '12345', the path parameter will be set to '12345'.

❓ Configuration

intermediate

Identify the correct response mapping template for a JSON error response

You want to map a backend error JSON response {"errorCode": "404", "message": "Not Found"} to a client response with status code 404 and a body containing only the message. Which response mapping template achieves this?

A

#set($inputRoot = $input.path('$'))
{
  "message": "$inputRoot.message"
}

B

{
  "error": "$input.path('$.errorCode')",
  "msg": "$input.path('$.message')"
}

C

#set($inputRoot = $input.path('$'))
{
  "errorMessage": "$inputRoot.errorCode"
}

D

{
  "message": "$input.path('$.errorMessage')"
}

💡 Hint

Look for the template that extracts the 'message' field correctly and formats the response body accordingly.

Option A correctly sets a variable to the root of the input JSON and then outputs only the 'message' field in the response body. Other options either extract wrong fields or format incorrectly.

❓ Architecture

advanced

Which architecture best supports dynamic request mapping for multiple backend services?

You need to design an API Gateway setup that routes requests to different backend services based on a request header value, and applies different request mapping templates accordingly. Which architecture pattern is best?

A Use a single API Gateway with multiple stages, each stage having its own mapping templates and backend integration.

B Use multiple API Gateways, each dedicated to one backend service with fixed mapping templates.

C Use a single API Gateway with multiple resources and methods, each configured with specific request mapping templates and backend integrations, and use request header-based mapping to select the resource.

D Use a single API Gateway with a Lambda authorizer that modifies the request and sets integration request parameters dynamically.

💡 Hint

Consider how API Gateway resources and methods can be configured to handle different request mappings and routing.

Option C uses multiple resources and methods within a single API Gateway, each with its own mapping templates and backend integrations. Request header-based mapping can be used to route requests to the correct resource. This is scalable and manageable.

❓ security

advanced

What security risk arises from improper request mapping in API Gateway?

If an API Gateway request mapping template does not properly validate or sanitize incoming JSON fields before passing them to the backend, what is the most likely security risk?

A Data loss because the mapping template deletes fields from the request.

B Denial of service due to large payloads being accepted by the mapping template.

C Unauthorized access because the mapping template bypasses authentication.

D Injection attacks such as SQL injection or command injection on the backend service.

💡 Hint

Think about what happens if malicious input is passed unchecked to backend services.

Improper validation or sanitization in request mapping can allow attackers to inject malicious code or queries, leading to injection attacks on backend services.

✅ Best Practice

expert

What is the best practice for managing complex response mapping templates in AWS API Gateway?

You have a complex backend response that requires multiple conditional transformations before sending to clients. What is the best practice to manage this complexity in API Gateway response mapping?

A Split the API Gateway method into multiple methods each handling a part of the transformation.

B Use a Lambda function as a proxy integration to handle response transformation outside API Gateway.

C Embed all logic directly in the response mapping template using Velocity Template Language (VTL) with nested conditionals.

D Disable response mapping and send backend responses directly to clients.

💡 Hint

Consider maintainability and complexity of VTL templates versus external processing.

Complex transformations are better handled in Lambda functions where code is easier to write, test, and maintain. Embedding complex logic in VTL is error-prone and hard to maintain.