ALB vs NLB vs CLB in AWS

AWS Elastic Load Balancer (ELB) provides multiple types of load balancers designed for different workloads and networking requirements.

The main AWS load balancer types are:

• Application Load Balancer (ALB)
• Network Load Balancer (NLB)
• Classic Load Balancer (CLB)

Why Different Load Balancers Exist

Different applications require different traffic handling.

Examples

High-Level Comparison

1. Application Load Balancer (ALB)

What is ALB?

ALB is a Layer 7 load balancer designed for:

• HTTP applications
• HTTPS applications
• Microservices
• Containers
• Kubernetes ingress

OSI Layer

Layer 7 — Application Layer
    

How ALB Works

Users
   |
Application Load Balancer
   |
Path/Host-Based Routing
   |
-------------------------------
|              |              |
Service-A    Service-B     Service-C
    

Key Features of ALB

• Path-based routing
• Host-based routing
• WebSocket support
• HTTP/2 support
• Container integration
• Lambda integration

Path-Based Routing Example

/api      → API Service
/orders   → Order Service
/payment  → Payment Service
    

Host-Based Routing Example

api.company.com     → API Service
admin.company.com   → Admin Service
    

Best Use Cases for ALB

• Microservices architecture
• REST APIs
• Web applications
• Containerized applications
• Kubernetes workloads

Advantages of ALB

• Advanced routing capabilities
• Application-aware traffic management
• Better microservices support
• Modern cloud-native integration

Disadvantages of ALB

• Slightly higher latency than NLB
• Only supports HTTP/HTTPS

2. Network Load Balancer (NLB)

What is NLB?

NLB is a Layer 4 load balancer optimized for:

• Ultra-high performance
• Low latency
• TCP/UDP traffic

OSI Layer

Layer 4 — Transport Layer
    

How NLB Works

Users
   |
Network Load Balancer
   |
TCP/UDP Forwarding
   |
-----------------------
|          |          |
Server1   Server2   Server3
    

Key Features of NLB

• Static IP support
• Ultra-low latency
• Millions of requests per second
• TLS support
• TCP and UDP support

Best Use Cases for NLB

• Gaming applications
• Real-time systems
• Financial systems
• IoT systems
• High-performance APIs

Advantages of NLB

• Extremely high performance
• Very low latency
• Supports non-HTTP traffic
• Static IP addresses

Disadvantages of NLB

• No advanced HTTP routing
• No path-based routing
• No application-layer intelligence

3. Classic Load Balancer (CLB)

What is CLB?

CLB is the older generation AWS load balancer.

It supports:

• Basic HTTP balancing
• Basic TCP balancing

OSI Layer

Layer 4 and Layer 7
    

Architecture

Users
   |
Classic Load Balancer
   |
-----------------------
|          |          |
EC2       EC2       EC2
    

Limitations of CLB

• No advanced routing
• No microservices support
• No container-native features
• Limited scalability

AWS Recommendation

Use ALB or NLB instead of CLB
    

Best Use Cases for CLB

• Legacy applications
• Older AWS architectures

Architecture Comparison

ALB Architecture

Internet
    |
ALB
    |
--------------------------------
|              |              |
Microservice1  Microservice2  Microservice3
    

NLB Architecture

Internet
    |
NLB
    |
-------------------------
|          |           |
TCP App1  TCP App2   TCP App3
    

CLB Architecture

Internet
    |
CLB
    |
----------------------
|         |          |
EC2       EC2       EC2
    

Detailed Comparison Table

Production Use Case Examples

ALB Example

E-Commerce Website
        |
ALB
        |
--------------------------------
|             |               |
Cart Service  Payment Service  Order Service
    

NLB Example

Gaming Platform
        |
NLB
        |
Real-Time TCP Servers
    

CLB Example

Legacy Monolithic Application
        |
CLB
        |
EC2 Instances
    

Load Balancer Selection Guide

Security Features Comparison

Production Best Practices

• Use ALB for HTTP/HTTPS applications
• Use NLB for TCP/UDP high-performance traffic
• Avoid CLB for new applications
• Enable multi-AZ deployment
• Configure health checks properly
• Use HTTPS and SSL certificates

Common Mistakes

• Using NLB for microservices routing
• Using CLB in modern architectures
• Improper health check configuration
• Ignoring SSL termination optimization

Interview Answer

AWS provides three major load balancer types:

• ALB (Application Load Balancer)
• NLB (Network Load Balancer)
• CLB (Classic Load Balancer)

ALB works at Layer 7 and is mainly used for HTTP/HTTPS web applications, microservices, and Kubernetes workloads.

NLB works at Layer 4 and is optimized for ultra-high performance, low latency, and TCP/UDP traffic.

CLB is the older generation AWS load balancer mainly used for legacy applications.

AWS generally recommends:

• ALB for modern web applications
• NLB for high-performance networking
• Avoid CLB for new architectures

Quick Summary Table

Useful Internal Links

• AWS Interview Questions
• Cloud Computing Interview Questions
• DevOps Interview Questions
• Docker Interview Questions
• Kubernetes Interview Questions

Final Conclusion

ALB, NLB, and CLB are designed for different networking requirements in AWS cloud environments.

Modern cloud-native architectures primarily use:

• ALB for intelligent HTTP routing
• NLB for ultra-fast TCP/UDP traffic

CLB is mainly maintained for backward compatibility and legacy workloads.

Choosing the correct load balancer is critical for:

• Application performance
• Scalability
• Security
• Cost optimization

Understanding ALB vs NLB vs CLB deeply is essential for AWS architects, DevOps engineers, cloud engineers, and infrastructure professionals.