DVA-C02 Development with AWS Services Practice Question

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

• ✗

  Return a string from the Lambda handler.

  Why it's wrong here

  When utilizing API Gateway's Lambda proxy integration, the Lambda function is expected to return a specific JSON structure that represents a complete HTTP response. A plain string output from the Lambda handler lacks essential HTTP components like a status code and response headers. Consequently, API Gateway cannot correctly interpret a simple string as a valid HTTP response, leading to an internal server error or an unexpected response format for the client, as it does not conform to the required proxy integration contract.

• ✓

  Return a dictionary containing 'statusCode', 'headers', and 'body' with 'body' as a JSON string.

  Why this is correct

  This format precisely adheres to the API Gateway Lambda proxy integration contract, where the Lambda function is solely responsible for constructing the entire HTTP response. By returning a dictionary containing `statusCode`, `headers` (as a dictionary of key-value pairs), and a `body` field (which itself must be a string, often a JSON string), the Lambda function provides all necessary information for API Gateway to directly pass through to the client. This ensures the client receives a properly formatted HTTP response with the correct status, custom headers, and a valid JSON payload.

• ✗

  Use API Gateway integration response and mapping templates to transform the Lambda output.

  Why it's wrong here

  With Lambda proxy integration, API Gateway passes the entire client request to the Lambda function and expects the function itself to return a properly formatted HTTP response, including the JSON body. Integration response and mapping templates are used only with non-proxy integration, where API Gateway transforms the Lambda output before sending it to the client. This option is tempting because mapping templates are a legitimate way to reshape responses in standard integrations, and would be correct if the developer had chosen the non-proxy integration type instead.

• ✗

  Return a JSON object from Lambda and set a Content-Type header in the API Gateway method response.

  Why it's wrong here

  Returning only a JSON object from Lambda, such as `{"key": "value"}`, does not satisfy the Lambda proxy integration contract, which mandates a specific envelope including `statusCode` and `headers`. While setting a `Content-Type` header in the API Gateway method response is relevant for non-proxy integrations to define the output type, it has no effect when Lambda proxy integration is enabled. In proxy integration, the Lambda function must explicitly define all response headers within its returned dictionary, making API Gateway's method response headers redundant for this purpose.

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