AWS Load Balancer Deep Dive: ALB vs NLB Explained

Load balancing is a core component of highly available and scalable cloud architectures. In AWS, Elastic Load Balancing (ELB) distributes incoming traffic across multiple compute resources to ensure reliability, performance, and fault tolerance. Among ELB types, the Application Load Balancer (ALB) and Network Load Balancer (NLB) are the most widely used for modern workloads.

This deep dive explains how ALB and NLB work, their key features, performance differences, ideal use cases, and how to choose the right one for your application in 2025.

Understanding AWS Elastic Load Balancing

AWS Elastic Load Balancing automatically distributes traffic across multiple targets such as EC2 instances, containers, Lambda functions, and IP addresses. It improves resilience by eliminating single points of failure and supports auto scaling for dynamic workloads.

ELB offers three main types of load balancers:

• Application Load Balancer (ALB)

• Network Load Balancer (NLB)

• Gateway Load Balancer (GWLB)

This article focuses on comparing ALB and NLB, the two most commonly used options.

What is an Application Load Balancer (ALB)

An Application Load Balancer operates at Layer 7 (Application Layer) of the OSI model. It understands HTTP, HTTPS, and gRPC traffic and is optimized for modern web applications and microservices.

ALB is ideal for advanced routing and intelligent traffic management.

Key Features of ALB

• Layer 7 content-based routing

• Host-based and path-based routing

• Native support for microservices and container workloads

• WebSocket and HTTP/2 support

• Authentication support with OIDC, Cognito, and social identity providers

• Central SSL/TLS termination

• Advanced request routing using rules and conditions

What is a Network Load Balancer (NLB)

A Network Load Balancer operates at Layer 4 (Transport Layer) and is designed for high-performance, low-latency applications. It handles TCP, UDP, and TLS traffic and can manage millions of requests per second while maintaining ultra-low latency.

NLB is commonly used for latency-sensitive workloads and system-level applications.

Key Features of NLB

• Layer 4 performance-based routing

• Capable of handling extremely high traffic volumes

• Preserves client source IP

• TLS offloading support

• Static and Elastic IP address support

• Zonal failover for resilient architecture

ALB vs NLB: Feature Comparison

When to Use ALB

Choose ALB when your workloads require:

• Intelligent Layer 7 traffic routing

• Traffic management based on content

• Microservices routing to containers or Lambda

• Web applications and modern API frameworks

• Authentication and authorization integration

• Advanced rule-based traffic steering

ALB is commonly deployed in microservices architectures using Amazon ECS or EKS.

When to Use NLB

Choose NLB for:

• High-performance, low-latency workloads

• TCP, UDP, or TLS-based applications

• Real-time streaming, VOIP, and gaming platforms

• Financial and trading systems

• Load balancing for on-premise or hybrid network traffic

• Applications needing static IP support or direct client IP visibility

NLB is ideal for enterprise systems requiring extreme performance and reliability.

ALB and NLB in Modern Architectures

Many modern applications use both ALB and NLB together. For example:

• ALB is used for web traffic routing and authentication

• NLB is used for backend services requiring fast, low-level connectivity

AWS also supports dual load balancer patterns, particularly in microservices, where ALB handles front-end traffic and NLB is used for backend service mesh routing.

Cost Considerations

ALB pricing is generally lower for typical web workloads because billing is based on:

• Load balancer hours

• LCU (Load Balancer Capacity Units)

NLB pricing tends to be higher, especially for high-volume traffic, since pricing is based on:

• Load balancer hours

• Processed LCU

• Data transfer

Selecting the right load balancer helps optimize both performance and costs.

Which Load Balancer Should You Choose in 2025

Here is a simplified decision guide:

Choose ALB if:
Your application needs advanced routing, API-level configuration, or authentication.

Choose NLB if:
Performance, low latency, static IPs, or TCP/UDP support is your top priority.

Many modern cloud-native solutions use ALB for public-facing traffic and NLB internally to support secure, fast communication across services.

Conclusion

Both Application Load Balancer and Network Load Balancer serve distinct purposes and excel in different environments. ALB is best suited for application-aware routing, whereas NLB is ideal for high-speed, low-latency workloads. Understanding their strengths will help AWS architects design resilient, scalable, and cost-efficient architectures in 2025.

For maximum flexibility, organizations often combine both load balancer types to meet the needs of modern distributed systems and microservices.