Lambda with API Gateway pattern in AWS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the role of AWS Lambda in the Lambda with API Gateway pattern?

AWS Lambda runs your backend code without managing servers. It executes your code in response to HTTP requests sent through API Gateway.

beginner

How does API Gateway interact with Lambda functions?

API Gateway acts as a front door that receives HTTP requests and forwards them to Lambda functions for processing, then returns the Lambda response to the client.

intermediate

Why is the Lambda with API Gateway pattern considered scalable?

Because Lambda automatically scales up or down based on incoming requests, and API Gateway handles routing and throttling, the system can handle many users without manual server management.

beginner

What is a common use case for the Lambda with API Gateway pattern?

Building RESTful APIs or microservices that respond to HTTP requests without managing servers, such as user authentication or data retrieval.

intermediate

What are some best practices when designing APIs with Lambda and API Gateway?

Use proper request validation, handle errors gracefully, enable caching in API Gateway, and keep Lambda functions stateless and focused on single tasks.

What triggers a Lambda function in the Lambda with API Gateway pattern?

A A manual server restart

B A scheduled cron job

C An HTTP request received by API Gateway

D A database update

In this pattern, API Gateway receives HTTP requests and triggers the Lambda function to handle them.

Which component handles routing and throttling in the Lambda with API Gateway pattern?

A API Gateway

B Elastic Load Balancer

C Amazon S3

D AWS Lambda

API Gateway manages routing requests to Lambda and can throttle requests to protect backend resources.

Why is Lambda considered serverless in this pattern?

A Because it runs on physical servers you manage

B Because you do not manage the underlying servers

C Because it only runs on your local machine

D Because it requires manual scaling

Lambda abstracts server management, so you only focus on code without managing servers.

What is a key benefit of using API Gateway with Lambda?

A It manages user authentication by default

B It automatically creates databases

C It replaces Lambda functions

D It provides a secure and scalable HTTP interface

API Gateway provides a secure, scalable HTTP endpoint that triggers Lambda functions.

Which of the following is a best practice for Lambda functions behind API Gateway?

A Handle errors gracefully

B Keep functions stateful

C Avoid request validation

D Use Lambda for long-running tasks

Handling errors gracefully improves API reliability and user experience.

Explain the flow of a user HTTP request through the Lambda with API Gateway pattern.

Think about each step from the user to the backend and back.

Describe why the Lambda with API Gateway pattern is suitable for scalable web APIs.

Consider how the system handles many users and traffic spikes.

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