AWS Load Balancer Deep Dive: Comparing ALB, NLB, and GWLB

Imagine a huge tech campus receiving thousands of visitors every day.

ALB is the receptionist. It asks where each visitor wants to go and sends them to the correct department.

NLB is the express highway. It moves a huge amount of traffic quickly without worrying about what each visitor wants.

GWLB is the security checkpoint. It sends visitors through security and inspection before allowing them to continue.

The easiest way to remember them is:

ALB = Smart Routing
NLB = Fast Traffic
GWLB = Security Traffic

Learn more about aws load balancer deep dive: alb vs nlb vs gwlb.

AWS Elastic Load Balancing distributes incoming traffic across multiple healthy servers or services.

Instead of sending every request to a single server:

  Users
    ↓
  Single Server

AWS can distribute the traffic:

  Users
    ↓
 Load Balancer
    ↓
 Server 1   Server 2   Server 3

This helps applications improve availability, reliability, and scalability.

Application Load Balancer — ALB

Think of ALB as a receptionist.

A visitor arrives and says:

“I want to visit the billing department.”

The receptionist understands the request and sends the visitor to the correct place.

ALB works in a similar way.

It operates at Layer 7 and understands HTTP and HTTPS requests. It can route traffic based on details such as the URL path or hostname.

Example

User
 ↓
ALB
 ├── /products → Product Service
 ├── /orders   → Order Service
 └── /users    → User Service

ALB is commonly used for

• Websites
• REST APIs
• Microservices
• Container applications
• HTTP/HTTPS traffic
• Path-based routing
• Host-based routing

Host-Based Routing Example

shop.example.com  → Shopping Servers
admin.example.com → Admin Servers

Simple rule: Choose ALB when the content of the HTTP request matters.

---

Network Load Balancer — NLB

Think of NLB as an express highway.

A highway does not ask why each car is travelling. Its main job is to move large amounts of traffic quickly and efficiently.

NLB works in a similar way.

It operates mainly at Layer 4 and handles network connections instead of inspecting application URLs.

Example

Clients
   ↓
  NLB
 ├── Server 1
 ├── Server 2
 └── Server 3

NLB supports protocols such as

• TCP
• UDP
• TLS

NLB is useful when you need

• High connection volumes
• Low latency
• High network performance
• Static IP addresses
• TCP or UDP traffic

Common examples include gaming platforms, IoT systems, streaming services, and high-performance network applications.

Simple rule: Choose NLB when network performance and connection handling matter more than HTTP-level routing.

---

Gateway Load Balancer — GWLB

Think of GWLB as a security checkpoint.

Before visitors enter a secure building, they may need to pass through a security inspection.

GWLB performs a similar role for network traffic.

Example

Internet
   ↓
 GWLB
   ↓
Security Appliance
   ↓
Application

Gateway Load Balancer is mainly designed to work with virtual network appliances.

Common use cases

• Firewalls
• Intrusion Detection Systems (IDS)
• Intrusion Prevention Systems (IPS)
• Traffic inspection appliances

Imagine a company running several firewall instances.

Instead of sending all network traffic through one firewall, GWLB can distribute the traffic across multiple healthy firewall appliances.

                ┌── Firewall 1
Traffic → GWLB ─┼── Firewall 2
                └── Firewall 3

This helps prevent one security appliance from becoming a bottleneck.

Simple rule: Choose GWLB when traffic needs to pass through firewalls, security systems, or network inspection appliances.

---

Each load balancer type enforces different execution boundaries:

• ALB terminates client connections and establishes new connections to targets, enabling advanced routing and SSL offloading.
• NLB preserves the client source IP by forwarding packets without terminating connections, supporting static IPs and high throughput.
• GWLB acts as a transparent gateway, forwarding traffic to virtual appliances without modifying packet headers, enabling seamless integration of third-party security and network functions.

Integration with AWS services varies: ALB tightly integrates with ECS and Lambda for serverless routing, NLB supports IP targets and static IPs for hybrid architectures, and GWLB integrates with virtual appliances deployed in VPCs.

AWS load balancers need to know which backend resources can receive traffic.

These resources are organized into target groups.

ALB
 ↓
Target Group
 ├── Server 1 ✓
 ├── Server 2 ✕
 └── Server 3 ✓

AWS performs health checks on the registered targets.

If Server 2 becomes unhealthy, the load balancer stops sending normal traffic to it and continues routing requests to healthy servers.

This helps keep the application available even when one server has a problem.

The decision becomes easier when you start with the type of traffic.

Building a website or REST API?
Choose ALB.

Handling TCP, UDP, TLS, or high-performance network traffic?
Choose NLB.

Routing traffic through firewalls or security appliances?
Choose GWLB.

A simple decision flow is:

HTTP / HTTPS?
     ↓
    ALB

TCP / UDP / TLS?
     ↓
    NLB
Firewall / Traffic Inspection?
     ↓
    GWLB

A Real-World Example

Imagine an online shopping company.

Its customer-facing website may use ALB:

Customer
   ↓
ALB
 ├── /products
 ├── /cart
 └── /orders

The company could use NLB for a high-performance internal network service.

It could also use GWLB to route traffic through security firewalls.

This means a large AWS architecture may use ALB, NLB, and GWLB together, because each one solves a different problem.

AWS ALB, NLB, and GWLB serve distinct roles in cloud architectures. ALB excels at HTTP/HTTPS application routing, NLB at high-performance TCP/UDP load balancing with source IP preservation, and GWLB at transparent network traffic forwarding to virtual appliances. Understanding their internal mechanisms, execution boundaries, and use cases is critical for designing scalable, secure, and cost-effective AWS environments.