Lambda integration in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ service_behavior

intermediate

Lambda Function Invocation Behavior

You have an AWS Lambda function integrated with an API Gateway using the default proxy integration. When a client sends a request, what will the Lambda function receive as its event parameter?

A An empty event object since API Gateway does not pass data by default.

B A JSON object containing HTTP method, headers, path, query parameters, and body as a string.

C Only the query parameters as a dictionary.

D The raw HTTP request body as a string only.

💡 Hint

Think about what information API Gateway sends to Lambda in proxy integration.

In proxy integration, API Gateway sends a detailed JSON event to Lambda including HTTP method, headers, path, query parameters, and the body as a string. This allows Lambda to handle the entire HTTP request.

❓ Architecture

intermediate

Choosing Lambda Integration Type

You want to integrate an AWS Lambda function with API Gateway. You need to support multiple HTTP methods and want API Gateway to handle request validation and transformation. Which integration type should you choose?

A AWS Service integration

B Lambda proxy integration

C Direct HTTP integration

D Lambda non-proxy (custom) integration

💡 Hint

Consider which integration type allows API Gateway to manage request validation and mapping templates.

Lambda non-proxy (custom) integration lets API Gateway handle request validation, transformation, and mapping templates before invoking Lambda. Proxy integration passes the entire request to Lambda without transformation.

❓ security

advanced

Securing Lambda Integration with API Gateway

You want to secure your Lambda function behind API Gateway so that only authenticated users can invoke it. Which of the following is the best way to enforce authentication at the API Gateway level?

A Use API Gateway Lambda authorizer to validate tokens before invoking Lambda.

B Add authentication logic inside the Lambda function code.

C Add an IAM policy to the Lambda function to allow only authenticated users.

D Make the Lambda function public and rely on network security groups.

💡 Hint

Think about where to enforce authentication to reduce Lambda load.

API Gateway Lambda authorizers validate tokens before invoking Lambda, preventing unauthorized requests early. IAM policies control AWS resource access but are less flexible for user authentication. Authentication inside Lambda increases latency and cost.

❓ Configuration

advanced

Configuring Lambda Integration Response

You have a Lambda function integrated with API Gateway using non-proxy integration. Your Lambda returns a JSON with a statusCode and body. How do you configure API Gateway to map the Lambda response to an HTTP 200 status with the body content?

A No configuration needed; API Gateway automatically maps Lambda response to HTTP response.

B Configure Lambda to return only the body string without statusCode.

C Set up a mapping template in Integration Response to extract body and set status code to 200.

D Use Lambda proxy integration instead to handle response automatically.

💡 Hint

Consider how API Gateway handles Lambda responses in non-proxy integration.

In non-proxy integration, API Gateway requires mapping templates in Integration Response to extract the body and set the HTTP status code. Proxy integration handles this automatically.

✅ Best Practice

expert

Optimizing Lambda Integration for Performance

You have a high-traffic API Gateway endpoint integrated with Lambda proxy integration. You notice increased latency and cold starts. Which approach best reduces latency and cold starts?

A Increase Lambda memory size and enable provisioned concurrency.

B Switch to Lambda non-proxy integration to reduce payload size.

C Add retries in API Gateway integration settings.

D Use API Gateway caching to store Lambda responses indefinitely.

💡 Hint

Think about how to keep Lambda functions warm and improve execution speed.

Increasing memory size can improve Lambda execution speed. Provisioned concurrency keeps Lambda instances initialized to avoid cold starts. Non-proxy integration does not reduce cold starts. Retries increase latency. Caching helps but indefinite caching is not practical for dynamic data.

Practice

1. What is the main purpose of Lambda integration in AWS API Gateway?

easy

A. To create virtual machines in the cloud

B. To store data permanently in AWS

C. To connect API Gateway to Lambda functions so they run code on requests

D. To monitor network traffic between AWS services

Solution

1. Step 1: Understand Lambda integration role

   Lambda integration allows API Gateway to trigger Lambda functions when an API request is made.

2. Step 2: Compare options with this role

   Only To connect API Gateway to Lambda functions so they run code on requests describes connecting API Gateway to Lambda to run code on requests.

3. Final Answer:

   To connect API Gateway to Lambda functions so they run code on requests -> Option C

4. Quick Check:

   Lambda integration = connect API Gateway to Lambda [OK]

Hint: Lambda integration runs code on API requests [OK]

Common Mistakes:

• Confusing Lambda integration with data storage
• Thinking it creates virtual machines
• Mixing it with monitoring services

2. Which of the following is the correct way to specify Lambda integration in an API Gateway method using AWS CLI?

easy

A. --integration-type HTTP --integration-uri http://example.com

B. --integration-type AWS_PROXY --integration-uri arn:aws:lambda:region:account-id:function:function-name

C. --integration-type MOCK --integration-uri arn:aws:s3:::bucket/key

D. --integration-type AWS --integration-uri arn:aws:ec2:region:account-id:instance/instance-id

Solution

1. Step 1: Identify Lambda integration syntax

   Lambda integration uses type AWS_PROXY and the Lambda function ARN as URI.

2. Step 2: Match options with correct syntax

   --integration-type AWS_PROXY --integration-uri arn:aws:lambda:region:account-id:function:function-name correctly uses AWS_PROXY and Lambda ARN format.

3. Final Answer:

   --integration-type AWS_PROXY --integration-uri arn:aws:lambda:region:account-id:function:function-name -> Option B

4. Quick Check:

   AWS_PROXY + Lambda ARN = correct syntax [OK]

Hint: AWS_PROXY + Lambda ARN = Lambda integration syntax [OK]

Common Mistakes:

• Using HTTP or MOCK integration types for Lambda
• Incorrect ARN format for Lambda function
• Confusing AWS integration with EC2 ARN

3. Given this AWS SAM template snippet, what will happen when the API Gateway endpoint is called?

{
  "Resources": {
    "MyFunction": {
      "Type": "AWS::Serverless::Function",
      "Properties": {
        "Handler": "index.handler",
        "Runtime": "nodejs18.x",
        "Events": {
          "ApiEvent": {
            "Type": "Api",
            "Properties": {
              "Path": "/hello",
              "Method": "get"
            }
          }
        }
      }
    }
  }
}

medium

A. API Gateway triggers the Lambda function on GET /hello requests

B. API Gateway returns a static response without calling Lambda

C. Lambda function is triggered only on POST requests

D. The template will fail to deploy due to missing integration

Solution

1. Step 1: Analyze the SAM template event

   The event defines an API trigger on path /hello with GET method linked to the Lambda function.

2. Step 2: Understand behavior on API call

   Calling GET /hello triggers the Lambda function as defined.

3. Final Answer:

   API Gateway triggers the Lambda function on GET /hello requests -> Option A

4. Quick Check:

   API event with GET triggers Lambda [OK]

Hint: API event with GET method triggers Lambda [OK]

Common Mistakes:

• Assuming static response without Lambda call
• Confusing HTTP methods for trigger
• Thinking deployment fails without explicit integration

4. You set up API Gateway with Lambda integration but get a 403 Forbidden error when calling the API. What is the most likely cause?

medium

A. API Gateway lacks permission to invoke the Lambda function

B. The API Gateway endpoint URL is incorrect

C. The Lambda function code has syntax errors

D. The Lambda function timeout is too short

Solution

1. Step 1: Understand 403 Forbidden meaning

   403 means access denied, often due to missing permissions.

2. Step 2: Check Lambda invoke permissions

   API Gateway must have permission to invoke Lambda; missing this causes 403 errors.

3. Final Answer:

   API Gateway lacks permission to invoke the Lambda function -> Option A

4. Quick Check:

   403 Forbidden = missing invoke permission [OK]

Hint: 403 Forbidden means missing invoke permission [OK]

Common Mistakes:

• Blaming Lambda code errors for 403
• Assuming wrong URL causes 403
• Thinking timeout causes 403 instead of 504

5. You want API Gateway to forward the full client request (headers, query, body) to your Lambda function and receive the Lambda response directly. Which integration type and setup should you use?

hard

A. Use AWS integration type with manual mapping templates

B. Use MOCK integration type and configure static responses

C. Use HTTP integration type pointing to Lambda's REST endpoint

D. Use AWS_PROXY integration type with Lambda and grant invoke permissions

Solution

1. Step 1: Identify integration type for full request forwarding

   AWS_PROXY integration forwards the entire client request to Lambda and returns Lambda's response directly.

2. Step 2: Confirm permissions and setup

   Granting API Gateway permission to invoke Lambda is required for this integration to work.

3. Final Answer:

   Use AWS_PROXY integration type with Lambda and grant invoke permissions -> Option D

4. Quick Check:

   AWS_PROXY + invoke permission = full request forwarding [OK]

Hint: AWS_PROXY forwards full request and response [OK]

Common Mistakes:

• Using MOCK for dynamic Lambda calls
• Using HTTP integration which doesn't call Lambda directly
• Using AWS integration without proxy causing manual mapping