Lambda concurrency and throttling in AWS - Mini Project: Build & Apply

AWS Lambda Concurrency and Throttling Setup

📖 Scenario: You are working as a cloud engineer for a company that needs to control how many AWS Lambda functions run at the same time. This helps avoid extra costs and keeps the system stable.

🎯 Goal: Build an AWS Lambda function configuration that sets a reserved concurrency limit to control how many instances can run simultaneously and configure a throttling behavior.

📋 What You'll Learn

Create a Lambda function resource named MyLambdaFunction with a basic handler and runtime.

Add a reserved concurrency limit of 5 to MyLambdaFunction.

Configure a dead letter queue (DLQ) using an existing SQS queue ARN arn:aws:sqs:us-east-1:123456789012:MyDLQ.

Set the maximum retry attempts to 2 in the event invoke configuration.

💡 Why This Matters

🌍 Real World

Controlling Lambda concurrency and throttling helps prevent unexpected costs and ensures your application remains stable under load.

💼 Career

Cloud engineers and DevOps professionals often configure Lambda concurrency and retry settings to optimize performance and reliability.

1

Create the basic AWS Lambda function resource

Create an AWS Lambda function resource named MyLambdaFunction with the handler set to index.handler and runtime set to nodejs18.x.

AWS

# Define the Lambda function resource
# Your code here

Hint

Use the aws_lambda_function resource with the exact name MyLambdaFunction.

2

Add reserved concurrency limit to the Lambda function

Add a reserved concurrency limit of 5 to the existing MyLambdaFunction resource.

AWS

resource "aws_lambda_function" "MyLambdaFunction" {
  function_name = "MyLambdaFunction"
  handler       = "index.handler"
  runtime       = "nodejs18.x"
  role          = "arn:aws:iam::123456789012:role/lambda-execution-role"
  filename      = "function.zip"
  # Add reserved concurrency limit here
  # Your code here
}

Hint

Add the reserved_concurrent_executions attribute with value 5 inside the Lambda resource.

3

Configure dead letter queue (DLQ) for the Lambda function

Add a dead letter configuration to MyLambdaFunction using the SQS queue ARN arn:aws:sqs:us-east-1:123456789012:MyDLQ.

AWS

resource "aws_lambda_function" "MyLambdaFunction" {
  function_name       = "MyLambdaFunction"
  handler             = "index.handler"
  runtime             = "nodejs18.x"
  role                = "arn:aws:iam::123456789012:role/lambda-execution-role"
  filename            = "function.zip"
  reserved_concurrent_executions = 5
  # Add dead letter config here
  # Your code here
}

Hint

Use the dead_letter_config block with target_arn set to the given SQS ARN.

4

Set maximum retry attempts for event invoke configuration

Create an aws_lambda_event_invoke_config resource for MyLambdaFunction that sets maximum_retry_attempts to 2.

AWS

resource "aws_lambda_function" "MyLambdaFunction" {
  function_name       = "MyLambdaFunction"
  handler             = "index.handler"
  runtime             = "nodejs18.x"
  role                = "arn:aws:iam::123456789012:role/lambda-execution-role"
  filename            = "function.zip"
  reserved_concurrent_executions = 5

  dead_letter_config {
    target_arn = "arn:aws:sqs:us-east-1:123456789012:MyDLQ"
  }
}

# Add event invoke config resource below
# Your code here

Hint

Create a separate resource named MyLambdaInvokeConfig for event invoke config with the specified retry attempts.

Practice

1. What does Lambda concurrency control in AWS Lambda functions?

easy

A. The total number of functions in an AWS account

B. The number of function instances that can run at the same time

C. The size of the function's deployment package

D. The amount of memory allocated to the function

Solution

1. Step 1: Understand Lambda concurrency concept

   Concurrency in Lambda means how many copies of your function can run simultaneously.

2. Step 2: Identify what concurrency controls

   It controls the number of function instances running at the same time to handle requests.

3. Final Answer:

   The number of function instances that can run at the same time -> Option B

4. Quick Check:

   Concurrency = simultaneous function runs [OK]

Hint: Concurrency = how many functions run at once [OK]

Common Mistakes:

• Confusing concurrency with memory size
• Thinking concurrency limits total functions
• Mixing concurrency with deployment package size

2. Which of the following is the correct way to set reserved concurrency for a Lambda function using AWS CLI?

easy

A. aws lambda update-function --name MyFunc --concurrency 5

B. aws lambda set-concurrency --function MyFunc --reserved 5

C. aws lambda put-function-concurrency --function-name MyFunc --reserved-concurrent-executions 5

D. aws lambda configure-concurrency --function MyFunc --limit 5

Solution

1. Step 1: Recall AWS CLI command for reserved concurrency

   The correct command is 'put-function-concurrency' with '--reserved-concurrent-executions' option.

2. Step 2: Match the correct syntax

   aws lambda put-function-concurrency --function-name MyFunc --reserved-concurrent-executions 5 matches the exact AWS CLI syntax to set reserved concurrency.

3. Final Answer:

   aws lambda put-function-concurrency --function-name MyFunc --reserved-concurrent-executions 5 -> Option C

4. Quick Check:

   Reserved concurrency CLI = put-function-concurrency [OK]

Hint: Use 'put-function-concurrency' with reserved count [OK]

Common Mistakes:

• Using wrong command names like 'set-concurrency'
• Incorrect option flags
• Confusing update-function with concurrency settings

3. Given a Lambda function with a reserved concurrency of 3, what happens if 5 requests arrive simultaneously?

medium

A. 3 requests run immediately; 2 are throttled and may be retried

B. All 5 requests run simultaneously without delay

C. Only 1 request runs; others are queued

D. All 5 requests are rejected immediately

Solution

1. Step 1: Understand reserved concurrency effect

   Reserved concurrency limits how many instances run at once; here it is 3.

2. Step 2: Analyze request handling

   When 5 requests come, 3 run immediately; the other 2 exceed limit and get throttled (rejected or retried).

3. Final Answer:

   3 requests run immediately; 2 are throttled and may be retried -> Option A

4. Quick Check:

   Requests > concurrency = throttling [OK]

Hint: Requests over concurrency limit get throttled [OK]

Common Mistakes:

• Assuming all requests run simultaneously
• Thinking requests queue automatically
• Believing throttled requests are dropped without retry

4. You set a reserved concurrency of 2 for a Lambda function but notice throttling errors even with only 2 requests at once. What is the likely cause?

medium

A. The reserved concurrency setting was not applied correctly

B. The account-level concurrency limit is lower than 2

C. The function timeout is set too high

D. The function's memory size is too small

Solution

1. Step 1: Check reserved concurrency application

   If throttling occurs at 2 requests, reserved concurrency might not be set or applied properly.

2. Step 2: Rule out other causes

   Memory size and timeout do not cause throttling; account limit lower than 2 is unlikely if 2 requests run.

3. Final Answer:

   The reserved concurrency setting was not applied correctly -> Option A

4. Quick Check:

   Throttling with low requests = misconfigured concurrency [OK]

Hint: Check if reserved concurrency is actually set [OK]

Common Mistakes:

• Blaming memory size for throttling
• Ignoring concurrency setting errors
• Assuming timeout causes throttling

5. You have two Lambda functions, A and B, sharing an account concurrency limit of 10. Function A has reserved concurrency 7. If both functions receive 7 simultaneous requests each, how many requests for function B will be throttled?

hard

A. 3 requests for function B will be throttled

B. 0 requests for function B will be throttled

C. 7 requests for function B will be throttled

D. 4 requests for function B will be throttled

Solution

1. Step 1: Understand reserved concurrency reservation

   Function A reserves 7 concurrency, so it can run up to 7 instances without throttling.

2. Step 2: Calculate remaining concurrency for function B

   Account limit is 10, so 10 - 7 = 3 concurrency left for function B.

3. Step 3: Analyze requests for function B

   Function B gets 7 requests but only 3 can run concurrently; 7 - 3 = 4 requests are throttled.

4. Final Answer:

   4 requests for function B will be throttled -> Option D

5. Quick Check:

   Reserved concurrency reduces available concurrency [OK]

Hint: Reserved concurrency reduces shared limit for others [OK]

Common Mistakes:

• Ignoring reserved concurrency reservation
• Assuming full account concurrency is available to all
• Miscounting throttled requests