AWS Lambda

Definition & Interview Answers for AWS Lambda

1. What is AWS Lambda?

AWS Lambda is a serverless computing service that lets you run code without provisioning or managing servers. It automatically scales, executes code in response to events (like API calls, file uploads, or database updates), and charges only for the execution time used.

💡 Example Answer: "AWS Lambda is a serverless compute service that automatically runs code in response to events. It eliminates the need for managing infrastructure and scales automatically, making it ideal for event-driven applications, real-time data processing, and backend services."

---

2. What are the Key Features of AWS Lambda?

Feature	Description
Serverless	No need to manage infrastructure; AWS handles scaling and availability.
Event-driven	Executes functions based on triggers from services like S3, DynamoDB, and API Gateway.
Auto-scaling	Automatically scales based on request load.
Pay-as-you-go	Charged based on execution time (milliseconds) and requests.
Supports Multiple Languages	Runs Python, Node.js, Java, Go, .NET, and custom runtimes.
Integration with AWS Services	Works with S3, DynamoDB, API Gateway, SNS, SQS, and more.

---

3. Comparison of Lambda vs EC2 vs ECS

Feature	Lambda	EC2	ECS (Containers)
Management	Fully managed, no infrastructure to manage	User manages OS, scaling, and instances	Manages containers but requires ECS/Fargate setup
Scalability	Automatic	Manual or Auto Scaling groups	Manual or Auto Scaling
Billing Model	Pay per execution (ms-based)	Pay per running instance	Pay per container/task
Use Case	Short-lived tasks, event-driven apps	Long-running applications	Microservices, containerized apps

---

4. AWS Lambda Limits & Quotas

Limit	Value
Max Function Timeout	15 minutes
Max Memory Allocation	10 GB
Max Execution Requests	1,000 concurrent executions (can request limit increase)
Max Deployment Package	50 MB (direct), 250 MB (with layers)
Max Environment Variables	4 KB

---

5. When to Use AWS Lambda?

• Event-driven processing (e.g., trigger functions when a file is uploaded to S3).

• API backend (e.g., handling HTTP requests via API Gateway).

• Real-time data processing (e.g., streaming data from Kinesis or DynamoDB).

• Scheduled tasks (e.g., automated backups, cron jobs using EventBridge).

• Chatbots and AI integrations (e.g., responding to messages using AI models).

---

6. Common Interview Questions on AWS Lambda

Q1: How does AWS Lambda scale automatically?

💡 Answer: "AWS Lambda scales by running multiple instances of a function in parallel. When requests increase, AWS Lambda launches new instances up to the concurrency limit. The default concurrency limit is 1,000, but it can be increased with AWS support."

Q2: What are cold starts in AWS Lambda? How do you minimize them?

💡 Answer: "A cold start occurs when AWS Lambda initializes a function for the first time, leading to higher latency. To minimize cold starts, you can use provisioned concurrency, optimize function size, and avoid VPC connections where possible."

Q3: How does AWS Lambda integrate with API Gateway?

💡 Answer: "API Gateway can trigger a Lambda function in response to HTTP requests. API Gateway receives the request, invokes the Lambda function, and returns the response to the client. This setup is commonly used for building serverless APIs."

Q4: What is the difference between Synchronous and Asynchronous invocation in AWS Lambda?

Invocation Type	Description	Example
Synchronous	The caller waits for the Lambda function to complete execution.	API Gateway, ALB, CloudFront
Asynchronous	The caller doesn’t wait; Lambda processes the event in the background.	S3, SNS, CloudWatch Events

Q5: How do you debug AWS Lambda functions?

💡 Answer: "You can debug AWS Lambda using AWS CloudWatch Logs, AWS X-Ray for tracing, and local testing with AWS SAM (Serverless Application Model). CloudWatch logs provide execution details, and X-Ray helps track request latency and bottlenecks."

Q6: Can AWS Lambda run inside a VPC?

💡 Answer: "Yes, AWS Lambda can be configured to run inside a VPC. This is required when accessing private resources like an RDS database. However, running Lambda in a VPC increases cold start times due to additional network configuration."

Q7: How can you secure an AWS Lambda function?

💡 Answer:

• Use IAM roles with least privilege.

• Enable VPC access control (if required).

• Encrypt environment variables with AWS KMS.

• Use API Gateway authentication for API-backed Lambda functions.

---

Would you like more scenario-based AWS Lambda interview questions? 🚀