Creating REST APIs: AWS API Gateway vs Direct AWS Lambda

If you're looking to build a REST API on AWS, you can do it either with AWS API Gateway or directly using AWS Lambda. Both methods can serve your API needs, but they work a little differently, especially when it comes to features, management, and scalability.

What is AWS API Gateway?

AWS API Gateway is a service that helps you manage APIs easily. It’s designed to handle everything around API management, like security, traffic control, and logging. It works with backend services, like Lambda, to run your API smoothly.

What is AWS Lambda?

AWS Lambda is a serverless compute service. It lets you run code without worrying about servers, and you only pay when your function is running. It’s great for event-driven tasks, and you can use it to expose REST APIs, but you’ll need to manage more things manually compared to API Gateway.

Key Differences

1. API Management and Features

• API Gateway: It’s built for managing APIs, giving you features like authentication, rate limiting, request validation, and caching right out of the box. You can set up different versions of your API and even deploy them to different environments (like production or testing).
• Lambda: When you use Lambda directly, you don’t get all those API management tools. You’ll need to code things like routing and request validation yourself. It’s simpler for small or internal services, but lacks the robust features of API Gateway.

2. Security and Access Control

• API Gateway: It offers a lot of built-in security. You can control who accesses your API with AWS IAM, API keys, or even create custom authorization through Lambda functions. It also supports HTTPS by default.
• Lambda: Lambda gives you some security options, but without API Gateway, you'll need to do more work to secure your API. You can still use IAM roles, but things like request signing and token management would require extra setup.

3. Costs

• API Gateway: API Gateway charges based on how many API calls are made, data transferred, and features like caching. For high-traffic applications, costs can rise, especially if you have many endpoints.
• Lambda: Direct Lambda is more cost-effective for small or simple applications since you’re only paying for Lambda execution time and data transfer. No extra costs for API management features you might not need.

4. Request Routing and Processing

• API Gateway: It acts as the middle layer between the client and your backend, routing each request to the right Lambda function or another backend service. You can easily create different routes and methods (like GET or POST).
• Lambda: If you're using Lambda URLs, you'll need to handle routing manually inside your Lambda function. This works well for simple, single-purpose APIs, but can get complicated as you add more endpoints.

5. Monitoring and Logging

• API Gateway: It automatically integrates with CloudWatch to log requests and metrics. You can easily track how your API is performing, look at errors, and even trace specific requests.
• Lambda: Lambda also integrates with CloudWatch, but doesn’t provide as much detailed API data unless you manually add logging in your code.

6. Performance and Latency

• API Gateway: It adds a small amount of latency because it sits between the client and Lambda. However, it’s usually not noticeable unless you need extremely low-latency performance.
• Lambda: Invoking Lambda directly is slightly faster since there’s no API Gateway in the middle, but the trade-off is that you lose the management features that API Gateway offers.

When to Use API Gateway

You should choose API Gateway if:

• You need to manage public-facing APIs with strong security features.
• Your API requires authentication, rate limiting, or caching.
• You want to monitor API performance closely and trace requests.
• You are managing multiple versions or environments for your API (e.g., development, production).

When to Use Direct AWS Lambda

Use Lambda directly if:

• You’re building a simple or internal service that doesn’t need all the features of API Gateway.
• You want to reduce costs and keep things lightweight.
• Low latency is a priority and you’re willing to manage the API logic manually.

Conclusion

In summary, if you need full API management with security, logging, and scalability, go with API Gateway. If you're building a small or internal service and want to keep things simple, direct Lambda might be the better choice. It all depends on your project’s needs, complexity, and scale.