Types of Load Balancers

By Pooja | 30th June 2025

1. Application Load Balancer (ALB)

An Application Load Balancer (ALB) is a load balancer that runs at the application layer (Layer 7) of the OSI model. ALBs support HTTP/HTTPS traffic and are able to forward traffic based on URL paths, headers, and query parameters.

Key features of ALBs are:

Content-based routing: ALBs can forward traffic based on the content of the request, including URL paths, headers, and query parameters.
Web Sockets and HTTP/2 support: ALBs provide support for WebSocket and HTTP/2, allowing for real-time communication and performance enhancements.
AWS service integration: ALBs can be integrated with other AWS services like EC2, S3, and Lambda.

Applications of ALBs are:

Web applications: ALBs are appropriate for web applications that involve sophisticated routing and content-based routing decisions.
Microservices architecture: Multiple microservices can be routed to using ALBs, allowing for a more scalable and flexible architecture.

2. Network Load Balancer (NLB)

A Network Load Balancer (NLB) is a load balancer that works at the transport layer (Layer 4) of the OSI model. NLBs are meant to deal with TCP, UDP, and TLS traffic and have the ability to forward traffic by IP addresses and ports.

Characteristics of NLBs are:

High-performance: NLBs support high-performance and low-latency traffic routing.
Static IP address support: NLBs can be allocated static IP addresses, allowing consistent and reliable access to applications.
Support for multiple protocols: NLBs can support multiple protocols, such as TCP, UDP, and TLS.

Applications of NLBs include:

Game applications: NLBs are ideally suited for game applications with low-latency and high-performance traffic routing.
Real-time communication: Traffic for real-time communication applications, such as live streaming and video conferencing, can be routed using NLBs.

3. Gateway Load Balancer (GWLB)

A Gateway Load Balancer (GWLB) is a load balancer specifically built for virtual appliances, like intrusion detection systems and firewalls. GWLBs support transparent load balancing, where traffic can be distributed across many virtual appliances without altering the packet headers.

Characteristics of GWLBs are:

Transparent load balancing: GWLBs support transparent load balancing, which allows traffic to be balanced across multiple virtual appliances without altering the packet headers.
Multi-protocol support: GWLBs support multiple protocols such as TCP, UDP, and ICMP.
Virtual appliance integration: GWLBs can be integrated with virtual appliances like firewalls and intrusion detection systems.

Applications of GWLBs are:

Virtual appliance installation: GWLBs are ideally suited for virtual appliance installations that need transparent load balancing and high availability.
Network security: GWLBs provide the ability to load balance traffic over multiple security appliances, providing more efficient network security.

4. Classic Load Balancer (CLB)

A Classic Load Balancer is a load balancer that works at the transport layer (Layer 4) of the OSI model. CLBs are capable of dealing with TCP and HTTP traffic and can direct traffic using IP addresses and ports.

Key features of CLBs are:

Fundamental load balancing: CLBs support basic load balancing functions, including support for TCP and HTTP traffic.
Multi-protocol support: CLBs can support various protocols like TCP and HTTP.

Applications of CLBs are:

Low-end load balancing: CLBs are suitable for low-end load balancing applications that do not need sophisticated routing or content-based routing decisions.
Legacy applications: CLBs can be utilized to host legacy applications that need simple load balancing features.

Conclusion

Selecting the right type of load balancer depends on your application’s architecture, performance needs, and security requirements.

ALBs are ideal for modern web apps and microservices with content-based routing.
NLBs suit high-performance, low-latency use cases like gaming or real-time communication.
GWLBs are tailored for security-focused deployments with virtual appliances.
CLBs, while legacy, still serve basic or transitional load balancing needs.

Understanding these options helps organizations build scalable, reliable, and secure cloud architectures.