AWS Elastic Load Balancer (ELB) vs. AWS API Gateway: Which Should You Use for Your Application?
When building and scaling applications on AWS, traffic management is a critical component. Amazon Web Services (AWS) provides two powerful tools for routing traffic: Elastic Load Balancer (ELB) and API Gateway. Both services play crucial roles in the management of incoming requests, but they cater to different types of use cases and have distinct features. Understanding the differences between these services is essential for selecting the right one for your application’s architecture.
In this post, we'll compare AWS Elastic Load Balancer (ELB) and AWS API Gateway based on several key factors, such as traffic routing, scalability, use cases, pricing models, and key features.
What is AWS Elastic Load Balancer (ELB)?
Amazon Elastic Load Balancer (ELB) is a service designed to automatically distribute incoming traffic across multiple targets, such as EC2 instances, containers, and IP addresses. It helps ensure that your application is highly available and fault-tolerant, by routing traffic efficiently across your resources.
ELB supports three main types:
Application Load Balancer (ALB) – Best for HTTP/HTTPS traffic, capable of routing traffic based on URL paths, hostnames, and more. It is ideal for modern, microservices-based applications.
Network Load Balancer (NLB) – Suitable for high-performance, low-latency applications. NLB is designed to handle millions of requests per second, routing traffic to targets such as EC2 instances and IP addresses over TCP/UDP.
Classic Load Balancer (CLB) – The legacy ELB offering that supports both HTTP/HTTPS and TCP traffic, but lacks some of the advanced features of ALB and NLB.
What is AWS API Gateway?
Amazon API Gateway is a fully managed service designed to create, deploy, and manage RESTful APIs for web applications. It is a serverless service that acts as an entry point for API requests, allowing developers to expose backend services securely, without worrying about the underlying infrastructure. API Gateway integrates seamlessly with AWS Lambda, AWS Step Functions, and other AWS services, making it ideal for building microservices-based, event-driven, or serverless applications.
API Gateway supports:
REST APIs – For handling HTTP requests.
WebSocket APIs – For real-time, bidirectional communication between clients and servers.
HTTP APIs – A more cost-effective, simplified version of REST APIs that is optimized for low-latency API requests.
Key Differences Between ELB and API Gateway
1. Traffic Routing:
ELB: Elastic Load Balancer is designed to distribute traffic across multiple resources (typically EC2 instances, containers, or IP addresses). It operates at different layers of the OSI model, depending on the type of load balancer:
Application Load Balancer (ALB) works at the HTTP/HTTPS layer and can route traffic based on request data like URL path, headers, and query parameters.
Network Load Balancer (NLB) operates at the TCP/UDP layer and is suited for high-performance, low-latency applications.
Classic Load Balancer (CLB) supports both HTTP/HTTPS and TCP traffic but lacks the advanced features of ALB and NLB.
API Gateway: API Gateway routes incoming HTTP(S) requests to backend services like AWS Lambda functions, HTTP servers, or other AWS resources. It’s purpose-built to manage and route API requests, providing a variety of advanced features for API management, security, and monitoring. It offers granular control over API resources, such as request validation, authorization, and response formatting.
2. Scalability:
ELB: Scales automatically based on incoming traffic, distributing it evenly across your EC2 instances or containers. As demand increases, the load balancer automatically adjusts to handle more traffic. It can scale to millions of requests per second (depending on the type of ELB), making it suitable for large-scale web applications or high-traffic services.
API Gateway: API Gateway is designed to scale seamlessly as well. It can handle thousands of concurrent API calls with minimal configuration. When combined with AWS Lambda, API Gateway can scale automatically and handle spikes in demand without the need to manage servers or capacity planning.
3. Use Cases:
ELB Use Cases:
Web Applications: ELB is ideal for traditional applications with backend resources such as EC2 instances. It efficiently balances load across multiple EC2 instances or containers.
Microservices: ALB supports routing traffic to different microservices based on the URL path or hostname, making it suitable for microservices architectures.
High-Performance Applications: NLB can handle millions of requests per second with low latency, making it ideal for applications requiring high performance, such as gaming and financial trading systems.
API Gateway Use Cases:
Serverless APIs: API Gateway is commonly used for building serverless applications. It can route traffic to AWS Lambda functions, which process the requests without the need for EC2 instances or servers.
RESTful APIs: When building REST APIs for web or mobile applications, API Gateway provides a complete solution for managing endpoints, security, and monitoring.
Real-time Communication: API Gateway’s WebSocket support allows developers to build real-time applications like messaging apps or live feeds.
4. Pricing Models:
ELB:
Pricing is based on the number of hours the load balancer is running and the amount of data processed (in GBs).
Additional costs may apply based on the type of ELB (ALB, NLB, or CLB) and the region.
Classic Load Balancer (CLB) may be more affordable in simpler setups, while ALB and NLB come with more advanced features that may increase costs.
API Gateway:
Pricing is based on the number of API requests (per million requests) and the data transfer (in GBs).
For HTTP APIs, pricing is typically cheaper compared to REST APIs due to the simplified nature of HTTP APIs.
WebSocket APIs have separate pricing for message transmission and connection management.
5. Features & Security:
ELB:
SSL Termination: ELB supports SSL termination, which offloads the decryption work from backend instances and improves performance.
Sticky Sessions: Allows session persistence for applications that require users to be routed to the same server for the duration of their session.
Health Checks: Monitors the health of EC2 instances and automatically stops sending traffic to unhealthy instances.
Security Groups: ELB integrates with security groups to control inbound and outbound traffic.
API Gateway:
Request Validation: Ensures that incoming API requests meet specific criteria before they are forwarded to backend services.
Authentication & Authorization: API Gateway integrates with AWS Cognito for user authentication, or it can use AWS IAM or Lambda functions for custom authorization.
Throttling & Rate Limiting: Protects backend systems from being overwhelmed by limiting the number of requests over a specified period.
API Keys: Supports API keys for controlling access and tracking usage.
When to Use ELB vs. API Gateway?
Use ELB when:
You need to route HTTP/HTTPS or TCP/UDP traffic to EC2 instances, containers, or IP addresses.
You’re working with a traditional application architecture where you manage servers and need to balance traffic across them.
You need to scale based on traffic and distribute it across multiple application layers, including EC2 instances, load-balanced containers, or on-premises resources.
Use API Gateway when:
You are building APIs or serverless applications, particularly if you're using AWS Lambda for backend processing.
You require a fully managed API management solution with features like request validation, rate limiting, and authorization.
You need to expose web services, such as REST APIs, or manage WebSocket connections for real-time communication.
Conclusion:
Both AWS Elastic Load Balancer (ELB) and AWS API Gateway are crucial for handling and routing traffic within AWS. However, their intended use cases are different. ELB excels in load balancing across EC2 instances or containers for traditional web applications and high-performance use cases, whereas API Gateway is ideal for managing APIs, especially in serverless architectures or when building real-time applications.
Choosing between the two depends on the nature of your application. If you're running a microservices or serverless architecture, API Gateway will likely be your go-to choice. For traditional applications that require load balancing across EC2 instances, ELB will be a more fitting solution.
By understanding their features, use cases, and pricing models, you can make an informed decision on the best service to manage traffic for your application.
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