Lambda with API Gateway pattern in AWS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the integration type for API Gateway to invoke Lambda.

AWS

IntegrationType = "[1]"

Drag options to blanks, or click blank then click option'

AHTTP

BHTTP_PROXY

CMOCK

DAWS_PROXY

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing HTTP or HTTP_PROXY which are for HTTP backends, not Lambda.

Using MOCK which is for testing without backend.

The integration type AWS_PROXY allows API Gateway to directly invoke Lambda functions.

2fill in blank

medium

Complete the code to define the HTTP method for the API Gateway resource.

AWS

httpMethod = "[1]"

Drag options to blanks, or click blank then click option'

AGET

BTRACE

CPOST

DCONNECT

Attempts:

3 left

💡 Hint

Common Mistakes

Using POST when the operation is a read-only fetch.

Choosing CONNECT or TRACE which are rarely used in API Gateway.

The GET method is commonly used to retrieve data via API Gateway.

3fill in blank

hard

Fix the error in the Lambda function handler signature.

AWS

def lambda_handler([1], context):
    return {'statusCode': 200, 'body': 'Hello from Lambda!'}

Drag options to blanks, or click blank then click option'

Arequest

Bevent

Cinput

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using names like request or input which are not standard and may confuse readers.

Forgetting the event parameter causes runtime errors.

The first parameter of a Lambda handler is conventionally named event, representing the input event.

4fill in blank

hard

Fill both blanks to create a resource path and attach a GET method in API Gateway.

AWS

resource = api.root.add_resource("[1]")
resource.add_method("[2]", lambda_integration)

Drag options to blanks, or click blank then click option'

Ausers

BPOST

CGET

Dorders

Attempts:

3 left

💡 Hint

Common Mistakes

Using POST method when the instruction asks for GET.

Choosing unrelated resource names like orders when users is expected.

The resource path users is created, and the GET method is attached to it.

5fill in blank

hard

Fill all three blanks to configure Lambda permissions for API Gateway invocation.

AWS

lambda_function.add_permission(
    Action="[1]",
    Principal="[2]",
    SourceArn="[3]"
)

Drag options to blanks, or click blank then click option'

Alambda:InvokeFunction

Bapigateway.amazonaws.com

Carn:aws:execute-api:region:account-id:api-id/*/GET/resource

Ds3:PutObject

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect actions like s3:PutObject which are unrelated.

Setting Principal to a user or role instead of API Gateway service.

Incorrect SourceArn format causing permission denial.

Lambda permission must allow lambda:InvokeFunction action, with apigateway.amazonaws.com as principal, and the API Gateway's SourceArn to restrict invocation.

Practice

1. What is the primary role of AWS API Gateway when used with Lambda in a serverless architecture?

easy

A. To receive HTTP requests and trigger Lambda functions

B. To store data permanently

C. To run long-running background tasks

D. To manage virtual machines

Solution

1. Step 1: Understand API Gateway's function

   API Gateway acts as a front door to accept and process HTTP requests from clients.

2. Step 2: Connect API Gateway to Lambda

   API Gateway triggers Lambda functions to execute backend logic upon receiving requests.

3. Final Answer:

   To receive HTTP requests and trigger Lambda functions -> Option A

4. Quick Check:

   API Gateway triggers Lambda = A [OK]

Hint: API Gateway handles HTTP, Lambda runs code [OK]

Common Mistakes:

• Confusing API Gateway with data storage
• Thinking Lambda manages servers
• Assuming API Gateway runs background tasks

2. Which of the following is the correct way to configure an API Gateway method to trigger a Lambda function?

easy

A. Set the integration type to HTTP and specify the Lambda URL

B. Set the integration type to VPC Link and attach Lambda

C. Set the integration type to Lambda Function and select the function ARN

D. Set the integration type to MOCK and provide Lambda code inline

Solution

1. Step 1: Identify correct integration type

   API Gateway uses 'Lambda Function' integration to directly invoke Lambda functions.

2. Step 2: Specify Lambda function ARN

   You must provide the ARN (Amazon Resource Name) of the Lambda function to link it properly.

3. Final Answer:

   Set the integration type to Lambda Function and select the function ARN -> Option C

4. Quick Check:

   Integration type Lambda Function + ARN = D [OK]

Hint: Use 'Lambda Function' integration with ARN [OK]

Common Mistakes:

• Using HTTP integration instead of Lambda Function
• Confusing MOCK integration with Lambda
• Incorrectly using VPC Link for Lambda

3. Consider this AWS Lambda function triggered by API Gateway:

exports.handler = async (event) => {
  return { statusCode: 200, body: JSON.stringify({ message: event.queryStringParameters.name }) };
};

What will be the response body if the API Gateway is called with URL ?name=Alice?

medium

A. {"message":"Alice"}

B. {"message":null}

C. {"message":"name"}

D. Error: event.queryStringParameters undefined

Solution

1. Step 1: Understand event object from API Gateway

   API Gateway passes query parameters inside event.queryStringParameters, so event.queryStringParameters.name equals 'Alice'.

2. Step 2: Check Lambda return value

   Lambda returns JSON string with message key set to 'Alice', so response body is '{"message":"Alice"}'.

3. Final Answer:

   {"message":"Alice"} -> Option A

4. Quick Check:

   Query param 'name=Alice' -> message = 'Alice' [OK]

Hint: Query params in event.queryStringParameters [OK]

Common Mistakes:

• Assuming queryStringParameters is null
• Returning raw object instead of JSON string
• Confusing parameter name with literal string

4. You deployed an API Gateway with Lambda integration but receive a 502 Bad Gateway error when calling the API. What is the most likely cause?

medium

A. API Gateway endpoint URL is incorrect

B. Lambda function is not returning a properly formatted response

C. Lambda function has no execution role assigned

D. API Gateway method is set to MOCK integration

Solution

1. Step 1: Understand 502 Bad Gateway meaning

   502 error usually means API Gateway received an invalid response from Lambda.

2. Step 2: Check Lambda response format

   Lambda must return an object with statusCode and body as string; missing or malformed response causes 502.

3. Final Answer:

   Lambda function is not returning a properly formatted response -> Option B

4. Quick Check:

   502 error = bad Lambda response format [OK]

Hint: 502 means Lambda response format error [OK]

Common Mistakes:

• Assuming wrong API Gateway URL causes 502
• Ignoring Lambda execution role issues (causes 403)
• Confusing MOCK integration with Lambda integration

5. You want to design a serverless API using API Gateway and Lambda that handles high traffic with unpredictable spikes. Which design choice best ensures scalability and cost efficiency?

hard

A. Use API Gateway with Lambda proxy integration and enable Lambda reserved concurrency

B. Use API Gateway with HTTP integration to EC2 instances behind an autoscaling group

C. Use API Gateway with MOCK integration and pre-warm Lambda functions manually

D. Use API Gateway with Lambda proxy integration and rely on Lambda's default scaling without reserved concurrency

Solution

1. Step 1: Understand Lambda scaling behavior

   Lambda scales automatically with incoming requests without needing reserved concurrency unless limiting concurrency is required.

2. Step 2: Evaluate cost and scalability

   Relying on default Lambda scaling avoids paying for reserved concurrency and handles unpredictable spikes efficiently.

3. Step 3: Compare other options

   EC2 autoscaling adds server management and cost; MOCK integration doesn't run real code; reserved concurrency limits scaling.

4. Final Answer:

   Use API Gateway with Lambda proxy integration and rely on Lambda's default scaling without reserved concurrency -> Option D

5. Quick Check:

   Default Lambda scaling + proxy integration = C [OK]

Hint: Default Lambda scaling handles spikes best [OK]

Common Mistakes:

• Setting reserved concurrency unnecessarily limits scaling
• Using EC2 adds complexity and cost
• Using MOCK integration doesn't run Lambda code