Why API Gateway matters in AWS - Why It Works

Introduction

When you build apps that talk to other apps or services, you need a way to manage those conversations safely and smoothly. API Gateway helps by acting like a smart gatekeeper that controls who can talk, what they can say, and how the messages get through.

When you want to let mobile apps securely access your backend services without exposing them directly

When you need to control and limit how many requests users can send to your service to avoid overload

When you want to transform or validate incoming requests before they reach your backend

When you want to collect data about how your APIs are used for monitoring and troubleshooting

When you want to connect multiple backend services under one easy-to-use URL

Commands

This command creates a new API Gateway REST API named MyExampleAPI in the us-east-1 region. It's the first step to set up your API Gateway.

Terminal

aws apigateway create-rest-api --name MyExampleAPI --region us-east-1

Expected Output

{

    "id": "a1b2c3d4e5",

    "name": "MyExampleAPI",

    "createdDate": "2024-06-01T12:00:00Z",

    "region": "us-east-1"

}

→

--name - Sets the name of the new API

→

--region - Specifies the AWS region where the API is created

This command lists all REST APIs in the us-east-1 region so you can verify that your API was created successfully.

Terminal

aws apigateway get-rest-apis --region us-east-1

Expected Output

{

    "items": [

        {

            "id": "a1b2c3d4e5",

            "name": "MyExampleAPI",

            "createdDate": "2024-06-01T12:00:00Z"

        }

    ]

}

→

--region - Specifies the AWS region to list APIs from

This command creates a new resource path called /example under the root resource of your API. Resources are like folders or endpoints in your API.

Terminal

aws apigateway create-resource --rest-api-id a1b2c3d4e5 --parent-id a1b2c3d4e5 --path-part example --region us-east-1

Expected Output

{

    "id": "f6g7h8i9j0",

    "parentId": "a1b2c3d4e5",

    "pathPart": "example",

    "path": "/example"

}

→

--rest-api-id - Specifies which API to add the resource to

→

--parent-id - Specifies the parent resource ID, usually the root

→

--path-part - Sets the name of the new resource path

→

--region - Specifies the AWS region

This command adds a GET method to the /example resource without requiring authorization. Methods define what actions users can perform on resources.

Terminal

aws apigateway put-method --rest-api-id a1b2c3d4e5 --resource-id f6g7h8i9j0 --http-method GET --authorization-type NONE --region us-east-1

Expected Output

{

    "httpMethod": "GET",

    "authorizationType": "NONE",

    "apiKeyRequired": false

}

→

--http-method - Defines the HTTP method like GET, POST, etc.

→

--authorization-type - Sets the security type; NONE means open access

This command lists all resources and methods in your API so you can check your setup.

Terminal

aws apigateway get-resources --rest-api-id a1b2c3d4e5 --region us-east-1

Expected Output

{

    "items": [

        {

            "id": "a1b2c3d4e5",

            "path": "/"

        },

        {

            "id": "f6g7h8i9j0",

            "path": "/example",

            "resourceMethods": {

                "GET": {}

            }

        }

    ]

}

→

--rest-api-id - Specifies which API to list resources from

→

--region - Specifies the AWS region

Key Concept

If you remember nothing else from this pattern, remember: API Gateway acts as a secure and manageable front door for your backend services.

Common Mistakes

Trying to create a resource without specifying the correct parent ID

The resource won't be created because the parent resource ID is required to place the new resource in the API structure

Always get the root resource ID first using 'aws apigateway get-resources' and use it as the parent ID

Not specifying the region in AWS CLI commands

Commands may fail or act on the wrong region, causing confusion or errors

Always include the --region flag or configure a default region in your AWS CLI settings

Setting authorization-type to NONE in production without other security measures

This leaves your API open to anyone, risking misuse or attacks

Use proper authorization methods like IAM roles, API keys, or Cognito for secure access

Summary

Create an API Gateway REST API to act as the entry point for your backend services.

Add resources and methods to define the API structure and allowed actions.

Use AWS CLI commands to create, verify, and manage your API setup step-by-step.

Practice

1. What is the primary role of an API Gateway in a cloud system?

easy

A. It replaces the need for backend servers.

B. It stores all the data for backend services.

C. It acts as a single entry point to manage and route API requests.

D. It directly processes user interface rendering.

Solution

1. Step 1: Understand API Gateway's function

   API Gateway acts as a front door that receives all API calls and routes them to appropriate backend services.

2. Step 2: Compare options with this role

   Only It acts as a single entry point to manage and route API requests. describes this role correctly; others describe unrelated functions.

3. Final Answer:

   It acts as a single entry point to manage and route API requests. -> Option C

4. Quick Check:

   API Gateway = Single entry point [OK]

Hint: API Gateway is the front door, not the data store [OK]

Common Mistakes:

• Confusing API Gateway with database storage
• Thinking API Gateway replaces backend servers
• Assuming API Gateway handles UI rendering

2. Which of the following is the correct way to define an API Gateway endpoint in AWS?

easy

A. Create a Lambda function and call it directly from the client.

B. Use S3 bucket URL as the API endpoint.

C. Set up an EC2 instance and expose its IP as the API endpoint.

D. Configure an API Gateway resource and method, then integrate with backend.

Solution

1. Step 1: Recall AWS API Gateway setup

   API Gateway requires defining resources and methods that connect to backend services like Lambda or HTTP endpoints.

2. Step 2: Evaluate options

   Configure an API Gateway resource and method, then integrate with backend. correctly describes configuring API Gateway resources and methods. Others describe unrelated or incorrect setups.

3. Final Answer:

   Configure an API Gateway resource and method, then integrate with backend. -> Option D

4. Quick Check:

   API Gateway setup = resource + method + backend integration [OK]

Hint: API Gateway needs resource and method setup, not direct Lambda calls [OK]

Common Mistakes:

• Calling Lambda directly without API Gateway
• Using EC2 IP as API endpoint without API Gateway
• Confusing S3 URLs with API endpoints

3. Given this AWS API Gateway setup: a GET method integrated with a Lambda function that returns {"status": "ok"}, what will the client receive when calling the endpoint?

medium

A. {"status": "ok"}

B. An error because API Gateway cannot integrate with Lambda

C. Empty response with status 200

D. HTML page instead of JSON

Solution

1. Step 1: Understand API Gateway and Lambda integration

   API Gateway forwards the request to Lambda, which returns a JSON response {"status": "ok"}.

2. Step 2: Determine client response

   The client receives the Lambda output as JSON through API Gateway, so the response is {"status": "ok"}.

3. Final Answer:

   {"status": "ok"} -> Option A

4. Quick Check:

   Lambda output = client response via API Gateway [OK]

Hint: API Gateway passes Lambda output as response [OK]

Common Mistakes:

• Thinking API Gateway blocks Lambda responses
• Expecting empty or HTML response by default
• Confusing integration types

4. You configured an API Gateway method but clients receive 403 Forbidden errors. What is the most likely cause?

medium

A. The client is sending requests with wrong HTTP method.

B. The API Gateway resource policy denies access to clients.

C. The backend database is down.

D. The Lambda function code has syntax errors.

Solution

1. Step 1: Analyze 403 Forbidden meaning

   403 means access is denied, often due to permissions or resource policies.

2. Step 2: Match cause to API Gateway

   API Gateway resource policies can restrict client access, causing 403 errors. Lambda errors or backend issues usually cause 500 errors, and wrong HTTP methods cause 405 errors.

3. Final Answer:

   The API Gateway resource policy denies access to clients. -> Option B

4. Quick Check:

   403 Forbidden = Access denied by policy [OK]

Hint: 403 means permission denied, check API Gateway policies [OK]

Common Mistakes:

• Confusing 403 with 500 or 405 errors
• Blaming Lambda code for 403 errors
• Ignoring API Gateway resource policies

5. You want to build a scalable system that handles thousands of API requests per second with security and monitoring. Why should you use AWS API Gateway instead of directly exposing backend services?

hard

A. API Gateway provides throttling, authentication, and detailed monitoring out of the box.

B. Direct backend exposure is faster and more secure than API Gateway.

C. API Gateway automatically writes backend code for you.

D. Backend services cannot handle API requests without API Gateway.

Solution

1. Step 1: Identify API Gateway features for scalability and security

   API Gateway offers throttling to limit request rates, authentication to secure access, and monitoring to track usage and errors.

2. Step 2: Compare with direct backend exposure

   Directly exposing backend services lacks these managed features, making scaling and security harder.

3. Step 3: Evaluate incorrect options

   Direct backend exposure is faster and more secure than API Gateway. is false because direct exposure is less secure. API Gateway automatically writes backend code for you. is false; API Gateway does not write backend code. Backend services cannot handle API requests without API Gateway. is false; backend can handle requests but less efficiently.

4. Final Answer:

   API Gateway provides throttling, authentication, and detailed monitoring out of the box. -> Option A

5. Quick Check:

   API Gateway = security + scaling + monitoring [OK]

Hint: API Gateway adds security and scaling features easily [OK]

Common Mistakes:

• Assuming direct backend is more secure
• Thinking API Gateway writes backend code
• Believing backend cannot handle requests alone