Top 15 Lambda Interview Questions: Ace Your Interview with Confidence

Lambda functions are a crucial aspect of serverless computing, and their popularity continues to grow in the tech industry. As a result, Lambda interview questions have become a common part of the hiring process for companies looking to fill serverless development roles. Whether you’re a seasoned developer or just starting out, it’s important to be well-prepared for Lambda-related interview questions to showcase your skills and expertise. In this article, we’ll explore the top 15 Lambda interview questions and provide you with detailed answers to help you ace your interview with confidence.

What is a Lambda Function?

A Lambda function is a small piece of code that runs in response to an event and is typically used in serverless computing. It allows you to build applications without the need to provision or manage servers. Lambda functions are event-driven, meaning they are triggered by events such as changes to data in an Amazon S3 bucket, updates to a DynamoDB table, or HTTP requests to an API Gateway.

When a Lambda function is invoked, AWS automatically provisions the necessary compute resources to run the code and then scales it in and out as required. Lambda functions are highly scalable, cost-effective, and allow developers to focus on writing code rather than managing infrastructure.

15 Common Interview Questions for Lambda Functions

1. What is the difference between a synchronous and asynchronous invocation in Lambda?

A synchronous invocation in Lambda means that the calling function waits for a response from the Lambda function before continuing execution. An asynchronous invocation, on the other hand, allows the calling function to continue execution without waiting for a response.

2. How can you pass data to a Lambda function?

Data can be passed to a Lambda function through event objects. These event objects can contain information such as the request payload, headers, and any other relevant data required by the function.

3. Can a Lambda function call another Lambda function?

Yes, a Lambda function can call another Lambda function. This is useful when you want to break down your application into smaller, more manageable functions that can be reused and independently scaled.

4. What is the maximum execution time for a Lambda function?

The maximum execution time for a Lambda function is 15 minutes.

5. How can you enable debugging in a Lambda function?

Debugging can be enabled in a Lambda function by using print statements or logging frameworks such as the AWS SDK for Python (Boto3). Logs can be viewed in Amazon CloudWatch for troubleshooting and debugging purposes.

6. What are the different triggers for a Lambda function?

A Lambda function can be triggered by various events, including changes to data in an Amazon S3 bucket, updates to a DynamoDB table, scheduled time-based events using Amazon CloudWatch Events, HTTP requests through API Gateway, and more.

7. How can you handle errors in a Lambda function?

Errors in a Lambda function can be handled by implementing error handling mechanisms such as try-catch blocks or using error handling features provided by the programming language you are using. Additionally, you can configure error notifications and alarms in Amazon CloudWatch to monitor and respond to errors.

8. What is the difference between environment variables and function parameters in Lambda?

Environment variables in Lambda are key-value pairs that can be used to store configuration values or sensitive information. They are accessible to the Lambda function throughout its execution. Function parameters, on the other hand, are values passed to the Lambda function at runtime and are specific to each invocation.

9. What is cold start in Lambda?

Cold start refers to the initial invocation of a Lambda function when AWS needs to provision the necessary compute resources to run the code. This can result in slightly longer execution times compared to subsequent invocations, which are known as warm starts.

10. How can you control the concurrency of a Lambda function?

The concurrency of a Lambda function can be controlled using the reserved concurrency feature. This allows you to limit the number of concurrent executions of a function, ensuring that it doesn’t exceed a specified threshold.

11. Can you use custom domains with API Gateway and Lambda?

Yes, you can use custom domains with API Gateway and Lambda by setting up a custom domain name in API Gateway and configuring the necessary DNS settings. This allows you to have a more branded and personalized API endpoint.

12. What are the security best practices for Lambda functions?

Some security best practices for Lambda functions include using IAM roles and policies to control permissions, encrypting sensitive data using AWS Key Management Service (KMS), and implementing proper input validation and output encoding to prevent common security vulnerabilities.

13. How can you handle versioning and aliasing in Lambda?

Versioning in Lambda allows you to manage different versions of your function code. Aliasing, on the other hand, allows you to create named references to specific versions of your function. This is useful when you want to perform A/B testing or gradually roll out new versions of your code.

14. Can you automate the deployment of Lambda functions?

Yes, the deployment of Lambda functions can be automated using AWS services such as AWS CloudFormation, AWS Serverless Application Model (SAM), or third-party tools like the Serverless Framework. These tools allow you to define and manage your serverless infrastructure as code.

15. How does AWS Lambda pricing work?

AWS Lambda pricing is based on the number of requests, the duration of the function execution, and the amount of memory allocated to the function. You only pay for the compute time consumed by your function and any additional AWS services or resources used within the function.

Tips for a Successful Lambda Interview

Preparing for a Lambda interview can significantly increase your chances of success. Here are some tips to help you prepare:

  • Understand Lambda concepts: Familiarize yourself with Lambda concepts, such as event-driven programming, triggers, and scalability.
  • Practice coding: Brush up on your coding skills, especially in the programming language you’ll be using for Lambda development.
  • Review AWS documentation: Go through the AWS Lambda documentation to gain a deeper understanding of the service and its features.
  • Build sample projects: Create small, sample Lambda functions to get hands-on experience and showcase your skills during the interview.
  • Stay updated: Keep up with the latest trends and updates in serverless computing and Lambda to demonstrate your enthusiasm and knowledge.
  • Ask questions: Prepare a list of questions to ask the interviewer to show your interest and engagement in the conversation.
  • Be confident: Believe in yourself and your abilities. Confidence goes a long way in interviews.


Preparing for Lambda interview questions is essential to stand out in the competitive tech industry. By familiarizing yourself with the common interview questions and practicing your answers, you can showcase your expertise and increase your chances of landing a serverless development role. Remember to stay calm, be confident, and demonstrate your passion for Lambda and serverless computing during the interview. Good luck!

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