Lambda integration in AWS - Mini Project: Build & Apply

AWS Lambda Integration with API Gateway

📖 Scenario: You are building a simple serverless application that responds to HTTP requests. You will create an AWS Lambda function and integrate it with an API Gateway to handle web requests.

🎯 Goal: Build an AWS Lambda function and connect it to an API Gateway REST API so that HTTP GET requests trigger the Lambda function.

📋 What You'll Learn

Create a Lambda function named MyLambdaFunction with a basic handler

Create an API Gateway REST API named MyApi

Add a GET method to the root resource of MyApi

Integrate the GET method with MyLambdaFunction

💡 Why This Matters

🌍 Real World

Serverless applications often use AWS Lambda with API Gateway to create scalable web APIs without managing servers.

💼 Career

Understanding Lambda integration with API Gateway is essential for cloud developers and architects building serverless backend services.

1

Create the AWS Lambda function

Create a Lambda function named MyLambdaFunction with a runtime of python3.12 and a handler named lambda_handler. The function should return a JSON response with status code 200 and body 'Hello from Lambda!'.

AWS

# Your code here to create MyLambdaFunction with python3.12 runtime and lambda_handler

Hint

Remember to create an IAM role for Lambda execution with the basic execution policy.

2

Create the API Gateway REST API

Create an API Gateway REST API resource named MyApi with a description 'API for Lambda integration'.

AWS

resource "aws_lambda_function" "MyLambdaFunction" {
  function_name = "MyLambdaFunction"
  runtime       = "python3.12"
  handler       = "lambda_handler"
  role          = aws_iam_role.lambda_exec.arn

  filename      = "lambda_function_payload.zip"

  source_code_hash = filebase64sha256("lambda_function_payload.zip")

  environment {
    variables = {}
  }
}

resource "aws_iam_role" "lambda_exec" {
  name = "lambda_exec_role"

  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = "sts:AssumeRole"
        Effect = "Allow"
        Principal = {
          Service = "lambda.amazonaws.com"
        }
      }
    ]
  })
}

resource "aws_iam_role_policy_attachment" "lambda_policy_attach" {
  role       = aws_iam_role.lambda_exec.name
  policy_arn = "arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole"
}

# Your code here to create MyApi REST API

Hint

Use aws_api_gateway_rest_api resource with the exact name MyApi.

3

Add GET method to API Gateway root resource

Add a GET method to the root resource of MyApi using aws_api_gateway_method. Set http_method to GET and authorization to NONE.

AWS

resource "aws_lambda_function" "MyLambdaFunction" {
  function_name = "MyLambdaFunction"
  runtime       = "python3.12"
  handler       = "lambda_handler"
  role          = aws_iam_role.lambda_exec.arn

  filename      = "lambda_function_payload.zip"

  source_code_hash = filebase64sha256("lambda_function_payload.zip")

  environment {
    variables = {}
  }
}

resource "aws_iam_role" "lambda_exec" {
  name = "lambda_exec_role"

  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = "sts:AssumeRole"
        Effect = "Allow"
        Principal = {
          Service = "lambda.amazonaws.com"
        }
      }
    ]
  })
}

resource "aws_iam_role_policy_attachment" "lambda_policy_attach" {
  role       = aws_iam_role.lambda_exec.name
  policy_arn = "arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole"
}

resource "aws_api_gateway_rest_api" "MyApi" {
  name        = "MyApi"
  description = "API for Lambda integration"
}

# Your code here to add GET method to root resource

Hint

Use aws_api_gateway_method with http_method = "GET" and authorization = "NONE".

4

Integrate GET method with Lambda function

Create an API Gateway integration resource named get_integration that connects the GET method of MyApi root resource to the Lambda function MyLambdaFunction. Use aws_api_gateway_integration with integration_http_method set to POST and type set to AWS_PROXY.

AWS

resource "aws_lambda_function" "MyLambdaFunction" {
  function_name = "MyLambdaFunction"
  runtime       = "python3.12"
  handler       = "lambda_handler"
  role          = aws_iam_role.lambda_exec.arn

  filename      = "lambda_function_payload.zip"

  source_code_hash = filebase64sha256("lambda_function_payload.zip")

  environment {
    variables = {}
  }
}

resource "aws_iam_role" "lambda_exec" {
  name = "lambda_exec_role"

  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = "sts:AssumeRole"
        Effect = "Allow"
        Principal = {
          Service = "lambda.amazonaws.com"
        }
      }
    ]
  })
}

resource "aws_iam_role_policy_attachment" "lambda_policy_attach" {
  role       = aws_iam_role.lambda_exec.name
  policy_arn = "arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole"
}

resource "aws_api_gateway_rest_api" "MyApi" {
  name        = "MyApi"
  description = "API for Lambda integration"
}

resource "aws_api_gateway_method" "get_root" {
  rest_api_id   = aws_api_gateway_rest_api.MyApi.id
  resource_id   = aws_api_gateway_rest_api.MyApi.root_resource_id
  http_method   = "GET"
  authorization = "NONE"
}

# Your code here to integrate GET method with Lambda

Hint

Use aws_api_gateway_integration with type = "AWS_PROXY" and integration_http_method = "POST".

Practice

1. What is the main purpose of Lambda integration in AWS API Gateway?

easy

A. To create virtual machines in the cloud

B. To store data permanently in AWS

C. To connect API Gateway to Lambda functions so they run code on requests

D. To monitor network traffic between AWS services

Solution

1. Step 1: Understand Lambda integration role

   Lambda integration allows API Gateway to trigger Lambda functions when an API request is made.

2. Step 2: Compare options with this role

   Only To connect API Gateway to Lambda functions so they run code on requests describes connecting API Gateway to Lambda to run code on requests.

3. Final Answer:

   To connect API Gateway to Lambda functions so they run code on requests -> Option C

4. Quick Check:

   Lambda integration = connect API Gateway to Lambda [OK]

Hint: Lambda integration runs code on API requests [OK]

Common Mistakes:

• Confusing Lambda integration with data storage
• Thinking it creates virtual machines
• Mixing it with monitoring services

2. Which of the following is the correct way to specify Lambda integration in an API Gateway method using AWS CLI?

easy

A. --integration-type HTTP --integration-uri http://example.com

B. --integration-type AWS_PROXY --integration-uri arn:aws:lambda:region:account-id:function:function-name

C. --integration-type MOCK --integration-uri arn:aws:s3:::bucket/key

D. --integration-type AWS --integration-uri arn:aws:ec2:region:account-id:instance/instance-id

Solution

1. Step 1: Identify Lambda integration syntax

   Lambda integration uses type AWS_PROXY and the Lambda function ARN as URI.

2. Step 2: Match options with correct syntax

   --integration-type AWS_PROXY --integration-uri arn:aws:lambda:region:account-id:function:function-name correctly uses AWS_PROXY and Lambda ARN format.

3. Final Answer:

   --integration-type AWS_PROXY --integration-uri arn:aws:lambda:region:account-id:function:function-name -> Option B

4. Quick Check:

   AWS_PROXY + Lambda ARN = correct syntax [OK]

Hint: AWS_PROXY + Lambda ARN = Lambda integration syntax [OK]

Common Mistakes:

• Using HTTP or MOCK integration types for Lambda
• Incorrect ARN format for Lambda function
• Confusing AWS integration with EC2 ARN

3. Given this AWS SAM template snippet, what will happen when the API Gateway endpoint is called?

{
  "Resources": {
    "MyFunction": {
      "Type": "AWS::Serverless::Function",
      "Properties": {
        "Handler": "index.handler",
        "Runtime": "nodejs18.x",
        "Events": {
          "ApiEvent": {
            "Type": "Api",
            "Properties": {
              "Path": "/hello",
              "Method": "get"
            }
          }
        }
      }
    }
  }
}

medium

A. API Gateway triggers the Lambda function on GET /hello requests

B. API Gateway returns a static response without calling Lambda

C. Lambda function is triggered only on POST requests

D. The template will fail to deploy due to missing integration

Solution

1. Step 1: Analyze the SAM template event

   The event defines an API trigger on path /hello with GET method linked to the Lambda function.

2. Step 2: Understand behavior on API call

   Calling GET /hello triggers the Lambda function as defined.

3. Final Answer:

   API Gateway triggers the Lambda function on GET /hello requests -> Option A

4. Quick Check:

   API event with GET triggers Lambda [OK]

Hint: API event with GET method triggers Lambda [OK]

Common Mistakes:

• Assuming static response without Lambda call
• Confusing HTTP methods for trigger
• Thinking deployment fails without explicit integration

4. You set up API Gateway with Lambda integration but get a 403 Forbidden error when calling the API. What is the most likely cause?

medium

A. API Gateway lacks permission to invoke the Lambda function

B. The API Gateway endpoint URL is incorrect

C. The Lambda function code has syntax errors

D. The Lambda function timeout is too short

Solution

1. Step 1: Understand 403 Forbidden meaning

   403 means access denied, often due to missing permissions.

2. Step 2: Check Lambda invoke permissions

   API Gateway must have permission to invoke Lambda; missing this causes 403 errors.

3. Final Answer:

   API Gateway lacks permission to invoke the Lambda function -> Option A

4. Quick Check:

   403 Forbidden = missing invoke permission [OK]

Hint: 403 Forbidden means missing invoke permission [OK]

Common Mistakes:

• Blaming Lambda code errors for 403
• Assuming wrong URL causes 403
• Thinking timeout causes 403 instead of 504

5. You want API Gateway to forward the full client request (headers, query, body) to your Lambda function and receive the Lambda response directly. Which integration type and setup should you use?

hard

A. Use AWS integration type with manual mapping templates

B. Use MOCK integration type and configure static responses

C. Use HTTP integration type pointing to Lambda's REST endpoint

D. Use AWS_PROXY integration type with Lambda and grant invoke permissions

Solution

1. Step 1: Identify integration type for full request forwarding

   AWS_PROXY integration forwards the entire client request to Lambda and returns Lambda's response directly.

2. Step 2: Confirm permissions and setup

   Granting API Gateway permission to invoke Lambda is required for this integration to work.

3. Final Answer:

   Use AWS_PROXY integration type with Lambda and grant invoke permissions -> Option D

4. Quick Check:

   AWS_PROXY + invoke permission = full request forwarding [OK]

Hint: AWS_PROXY forwards full request and response [OK]

Common Mistakes:

• Using MOCK for dynamic Lambda calls
• Using HTTP integration which doesn't call Lambda directly
• Using AWS integration without proxy causing manual mapping