[DEVELOPER] Advanced Lambda

Question 1

What are the three main types of Lambda invocation?

Answer 1

1. Synchronous (RequestResponse), 2. Asynchronous (Event), 3. Event Source Mapping (Poll-based).

Question 2

What happens to asynchronous events that fail after all retries?

Answer 2

They are sent to a Dead Letter Queue (SQS or SNS) or a Lambda Destination (SQS, SNS, another Lambda, or EventBridge).

Question 3

What is the default retry behavior for an Asynchronous Lambda invocation?

Answer 3

2 retries over a period of up to 6 hours.

Question 4

What two services can be used as a Dead Letter Queue (DLQ) for Lambda?

Answer 4

SQS (Queue) and SNS (Topic).

Question 5

When a Lambda is triggered by an SQS Queue, who manages retries?

Answer 5

The Lambda Event Source Mapping manages the retries; the SQS queue will handle the message’s visibility timeout and redelivery until it reaches the queue’s Redrive Policy (DLQ).

Question 6

What is a “Cold Start” in AWS Lambda?

Answer 6

The time taken for Lambda to download the code and initialize the runtime and execution environment before running the handler function.

Question 7

How do you minimize cold starts for a critical Lambda function?

Answer 7

Configure Provisioned Concurrency. This keeps a specified number of execution environments initialized and ready to respond.

Question 8

What is the difference between Reserved Concurrency and Provisioned Concurrency?

Answer 8

Reserved: A hard limit on the maximum concurrent executions for a function (prevents throttling).
Provisioned: Keeps environments warm and ready (solves cold starts).

Question 9

What is a Lambda Layer?

Answer 9

A ZIP file archive containing supplementary code, libraries, or custom runtimes that can be shared across multiple Lambda functions.

Question 10

What is required for a Lambda function to access resources inside a VPC?

Answer 10

The function must be configured with the appropriate VPC Subnets and Security Groups.

Question 11

If a VPC-configured Lambda needs to access the public internet (e.g., S3 or a public API), what is required?

Answer 11

It must route traffic through a Private Subnet → NAT Gateway → Internet Gateway.

Question 12

What service is used to manage and rotate database credentials for a Lambda function?

Answer 12

AWS Secrets Manager

Question 13

What is the best way to secure a secret (like a database connection string) used by a Lambda function?

Answer 13

Store it in AWS Secrets Manager or SSM Parameter Store (SecureString), and grant the Lambda Execution Role permissions to decrypt/retrieve it.

Question 14

What is the use case for AWS Lambda Reserved Concurrency?

Answer 14

To protect downstream resources from overload

Question 15

What is the use case for AWS Lambda Provisioned Concurrency?

Answer 15

Eliminate cold starts for critical, low-latency functions

Question 16

Suppose you have a lambda triggered by an SQS queue. Where do you configure sending messages to a DLQ after X failures?

Answer 16

In SQS (NOT Lambda!)

Question 17

A developer wants to debug a Lambda function using the AWS CLI. They invoke the function with ‘RequestResponse’ invocation type. How can they view the logs in the CLI response?

Answer 17

Use the --log-type Tail parameter.

Question 18

What AWS CLI command retrieves the error message from a failed Lambda invocation?

Answer 18

You must decode the x-amz-function-error header.

Question 19

What is the maximum size of the deployment package for a Lambda function (zipped)?

Answer 19

50 MB

Question 20

What is the maximum size of the deployment package for a Lambda function (unzipped)?

Answer 20

250MB

Question 21

You have a Lambda function configured with 128 MB of memory. The function is CPU bound and performing slowly. How can you increase the CPU power allocated to the function?

Answer 21

Increase the allocated memory.

In Lambda, CPU power is allocated proportionally to memory. Increasing memory automatically increases CPU.

Question 22

A developer wants to ensure that their Lambda function has access to the /tmp directory with a size of 2 GB. How can this be configured?

Answer 22

Configure the Ephemeral Storage setting in the function configuration.

You can configure ephemeral storage (/tmp) between 512 MB and 10 GB.

Question 23

You have a Lambda function that consumes messages from an SQS FIFO queue. What is the maximum concurrency limit for this function?

Answer 23

It is equal to the number of active Message Groups in the queue.

For FIFO queues, Lambda scales up to the number of active message groups to ensure order is preserved per group.