Difference between API Gateway and Load Balancer in System Design

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Hello folks, if you are preparing for System design interviews then you must have come across popular questions like difference between API Gateway vs Load Balancer, horizontal scalability vs vertical scaling, and Reverse Proxy vs Forward Proxy.

Earlier, I have shared popular System design interview problems and in this article, I will answer the first question so that you not only can answer this question on interviews but also learn this important concept well.

In the web services world and network infrastructure, two crucial components often come into play: API gateways and load balancers.

While they both play critical roles in managing and optimizing traffic flow, they serve distinct purposes and operate at different layers of the technology stack.

Understanding the difference between these two components is not just important for System design interview but also essential for designing robust and scalable architectures. Let's delve into the nuances of API gateways and load balancers to demystify their differences.

But, let's first see what is API Gateway?

Btw, here is also a nice diagram from DesignGuru, one of the best place to prepare for system design interviews. This diagram highlights the key difference between API Gateway and Load balancer,

What is API Gateway? How does it work?

An API gateway acts as a middleware component that sits between clients and backend services, providing a centralized entry point for accessing various endpoints and functionalities. Its primary function is to facilitate communication, security, and management of APIs. Here are key aspects of API gateways:

API Management
API gateways offer features for managing APIs, including authentication, authorization, rate limiting, and caching. They serve as a control point for enforcing security policies and access control measures.
Protocol Transformation
API gateways can handle protocol translation, allowing clients to communicate with backend services using different protocols or message formats. This capability enhances interoperability in heterogeneous environments.
Routing and Versioning
With an API gateway, requests can be routed to the appropriate backend service based on predefined rules and configurations.

Additionally, versioning support enables the coexistence of multiple API versions, ensuring backward compatibility and smooth migrations.

Analytics and Monitoring API gateways provide insights into API usage, performance metrics, and error tracking. This visibility enables operators to monitor the health of APIs, identify bottlenecks, and optimize resource utilization.

Here is a nice diagram of how API Gateway looks like:

What is Load Balancer? How it works?

A load balancer acts as a traffic distributor, evenly distributing incoming requests across multiple backend servers or instances to optimize resource utilization, improve availability, and enhance performance. Here are key aspects of load balancers:

Traffic Distribution
Load balancers distribute incoming traffic across multiple backend servers or instances based on predefined algorithms such as round-robin, least connections, or weighted distribution. This ensures efficient utilization of resources and prevents overloading of individual servers.
High Availability
Load balancers enhance the availability of services by intelligently routing traffic away from unhealthy or overloaded servers. They perform health checks to monitor the status of backend instances and dynamically adjust traffic routing accordingly.
Session Persistence
In scenarios where maintaining session state is crucial, load balancers support session persistence or sticky sessions, ensuring that subsequent requests from the same client are directed to the same backend server. This ensures consistency and avoids session-related issues.
SSL Termination
Load balancers can offload SSL/TLS encryption and decryption, relieving backend servers from the computational overhead associated with SSL processing. This improves performance and simplifies management of SSL certificates.

Here is how a load balancer look like and how it works:

Difference between API Gateway and Load Balancer?

While API gateways and load balancers share some similarities in terms of traffic management, their primary objectives and functionalities differ:

API Gateway: Focuses on API management, security, protocol transformation, and analytics. Ideal for exposing and managing APIs to external clients, enforcing access control policies, and providing a unified interface for diverse backend services.
Load Balancer: Primarily concerned with traffic distribution, high availability, and scalability. Suitable for distributing incoming traffic across multiple backend servers or instances to improve performance, reliability, and fault tolerance.

Here is also a nice diagram to highlight the difference between API Gateway and Load Balancer from ByteByteGo, one of the best place to prepare for System design interviews

Conclusion

In summary, both API gateways and load balancers are fundamental components in modern network architectures, each serving distinct purposes and offering unique capabilities. While API gateways specialize in API management and security, load balancers excel at distributing traffic for improved availability and scalability. Understanding their differences is essential for designing resilient and efficient systems that meet the evolving demands of modern applications and services.