Modern backend architectures often use reverse proxies, load balancers, and API gateways.
They are related, often used together, but they solve different problems at different layers.

This article explains:

• What each component does
• How they differ
• When to use each one
• Common load balancing algorithms

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Reverse Proxy

A reverse proxy sits in front of one or more backend servers and forwards client requests to them.
Clients never communicate directly with the backend services.

Responsibilities

• Acts as a single entry point
• Hides internal services and network topology
• TLS/SSL termination
• Caching and compression
• Basic authentication
• Request routing

What it does not focus on

• Advanced traffic distribution strategies
• API-level concerns like rate limiting or versioning

Example

Client → Reverse Proxy → Application Server

When to use it

• You want to hide backend services
• You need SSL termination
• You want caching or static content delivery
• You want simple routing based on path or host

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Load Balancer

A load balancer distributes incoming traffic across multiple instances of the same service to improve scalability, availability, and fault tolerance.

Responsibilities

• Distribute traffic across service replicas
• Perform health checks
• Detect failures and reroute traffic
• Enable horizontal scaling
• Support zero-downtime deployments

Example

Client → Load Balancer → App Instance 1
                         App Instance 2
                         App Instance 3

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Load Balancing Algorithms

Load balancers use algorithms to decide which backend instance should handle each request.

Round Robin

Requests are distributed sequentially across all available instances.

Request 1 → Instance A
Request 2 → Instance B
Request 3 → Instance C
Request 4 → Instance A

Pros

• Simple
• Even distribution

Cons

• Ignores current load

Best for

• Stateless services
• Uniform request cost

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Least Connections

Each request is routed to the instance with the fewest active connections.

Pros

• Adapts to uneven workloads
• Better for long-running requests

Cons

• Slightly more complex
• Requires tracking active connections

Best for

• APIs with variable processing time
• WebSockets or long-lived connections

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IP Hash

The client’s IP address is hashed to decide which backend handles the request.

hash(client_ip) → backend instance

Pros

• Session persistence (sticky sessions)
• Same client consistently hits the same backend

Cons

• Uneven load distribution
• Scaling up/down can reshuffle traffic

Best for

• Stateful applications
• Legacy systems without shared session storage

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API Gateway

An API Gateway is a specialized entry point designed for APIs, especially in microservices architectures.

It often includes reverse proxy and load balancing capabilities, but adds API-level intelligence.

Responsibilities

• Authentication and authorization (JWT, OAuth2, API keys)
• Rate limiting and throttling
• Request and response transformation
• API versioning (/v1, /v2)
• Routing to multiple backend services
• Monitoring, logging, and analytics

Example

Client → API Gateway
           ├── Auth Service
           ├── Orders Service
           └── Payments Service

When to use it

• You expose public or partner APIs
• You run microservices
• You need security, rate limiting, and versioning
• You want a clean separation between clients and services

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Comparison Table

Feature	Reverse Proxy	Load Balancer	API Gateway
Entry point	✅	✅	✅
Distributes traffic	⚠️ Basic	✅	✅
Hides backend	✅	❌	✅
API authentication	❌	❌	✅
Rate limiting	❌	❌	✅
Request transformation	❌	❌	✅
Best suited for	Infrastructure	Scalability	APIs & Microservices

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Mental Model

• Reverse Proxy → Traffic director
• Load Balancer → Traffic distributor
• API Gateway → Traffic manager with rules

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Common Real-World Setup

These components do not compete — they complement each other and are often used together in modern systems.

References

• NGINX Reverse Proxy Docs
• AWS What is Load Balancing
• AWS API Gateway Overview
• Reverse Proxy vs API Gateway vs Load Balancer - ByteByteGo channel