Lambda integration in AWS - Commands & Configuration

Introduction

Sometimes you want your cloud app to run code automatically when something happens, like a file upload or a web request. AWS Lambda lets you run small pieces of code without managing servers. Lambda integration means connecting Lambda to other AWS services so your code runs at the right time.

When you want to run code automatically after a user uploads a file to storage.

When you want to process data as soon as it arrives in a database.

When you want to respond to web requests without managing servers.

When you want to automate tasks triggered by changes in your cloud environment.

When you want to connect your code to events from other AWS services easily.

Config File - lambda-integration.yaml

lambda-integration.yaml

Resources:
  MyLambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: example-lambda
      Runtime: python3.9
      Handler: index.handler
      Role: arn:aws:iam::123456789012:role/lambda-execution-role
      Code:
        ZipFile: |
          def handler(event, context):
              print("Hello from Lambda")
              return {'statusCode': 200, 'body': 'Hello World'}

  MyApiGateway:
    Type: AWS::ApiGateway::RestApi
    Properties:
      Name: example-api

  MyApiResource:
    Type: AWS::ApiGateway::Resource
    Properties:
      ParentId: !GetAtt MyApiGateway.RootResourceId
      PathPart: hello
      RestApiId: !Ref MyApiGateway

  MyApiMethod:
    Type: AWS::ApiGateway::Method
    Properties:
      HttpMethod: GET
      ResourceId: !Ref MyApiResource
      RestApiId: !Ref MyApiGateway
      AuthorizationType: NONE
      Integration:
        Type: AWS_PROXY
        IntegrationHttpMethod: POST
        Uri: !Sub arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${MyLambdaFunction.Arn}/invocations

  LambdaPermission:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !Ref MyLambdaFunction
      Action: lambda:InvokeFunction
      Principal: apigateway.amazonaws.com
      SourceArn: !Sub arn:aws:execute-api:${AWS::Region}:${AWS::AccountId}:${MyApiGateway}/*/GET/hello

This YAML file creates a Lambda function that runs Python code printing a message and returning a response.

It sets up an API Gateway REST API with a resource path '/hello' and a GET method.

The GET method is integrated with the Lambda function using AWS_PROXY, which means the API Gateway forwards requests directly to Lambda.

LambdaPermission allows API Gateway to invoke the Lambda function securely.

Commands

This command deploys the CloudFormation stack that creates the Lambda function, API Gateway, and permissions. It sets up the integration automatically.

Terminal

aws cloudformation deploy --template-file lambda-integration.yaml --stack-name example-lambda-stack --capabilities CAPABILITY_NAMED_IAM

Expected Output

Waiting for stack create/update to complete...

Successfully created/updated stack - example-lambda-stack

→

--template-file - Specifies the CloudFormation template file to deploy

→

--stack-name - Names the CloudFormation stack

→

--capabilities - Allows creation of IAM roles needed by Lambda

This command lists the API Gateway REST APIs to find the API ID needed to call the endpoint.

Terminal

aws apigateway get-rest-apis

Expected Output

{

    "items": [

        {

            "id": "a1b2c3d4e5",

            "name": "example-api",

            "description": ""

        }

    ]

}

This command calls the API Gateway endpoint that triggers the Lambda function, showing the Lambda response.

Terminal

curl https://a1b2c3d4e5.execute-api.us-east-1.amazonaws.com/prod/hello

Expected Output

{"statusCode":200,"body":"Hello World"}

Key Concept

If you remember nothing else from this pattern, remember: Lambda integration lets you run code automatically in response to events from other AWS services without managing servers.

Common Mistakes

Not granting API Gateway permission to invoke the Lambda function.

API Gateway cannot call Lambda without explicit permission, causing errors when invoking the function.

Add a Lambda permission resource allowing API Gateway to invoke the function, specifying the correct source ARN.

Using the wrong URI format for Lambda integration in API Gateway.

API Gateway will fail to connect to Lambda if the URI is incorrect, causing 502 errors.

Use the correct URI format: arn:aws:apigateway:{region}:lambda:path/2015-03-31/functions/{function_arn}/invocations

Not deploying the API stage before calling the endpoint.

The API endpoint won't be available until the API is deployed, causing 404 errors.

Deploy the API stage (e.g., 'prod') in API Gateway before testing the endpoint.

Summary

Create a Lambda function and an API Gateway REST API with a resource and method.

Integrate the API Gateway method with the Lambda function using AWS_PROXY integration.

Grant API Gateway permission to invoke the Lambda function.

Deploy the CloudFormation stack to set up all resources.

Call the API Gateway endpoint to trigger the Lambda function and get the response.

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