AWS Gateway Load Balancer (GWLB) Explained

The Gateway Load Balancer (GWLB) is a specialized load balancer in AWS designed to deploy, scale, and manage third-party network security appliances such as firewalls, intrusion detection/prevention systems (IDPS), and deep packet inspection systems.

Why Use a Gateway Load Balancer?

A GWLB is useful when you want all network traffic to pass through a security layer before reaching your applications. Examples include:

• Firewall Inspection – Block unauthorized traffic.
• Intrusion Detection/Prevention (IDPS) – Identify and mitigate threats.
• Deep Packet Inspection – Examine packet content for policy enforcement.
• Payload Modification – Alter network traffic before delivery.

How the Gateway Load Balancer Works

Without a GWLB, sending traffic through security appliances requires complex routing. With GWLB, traffic flows seamlessly through virtual appliances before reaching the application.

Traffic Flow in GWLB Architecture

1. Users send requests to the application.
2. All traffic is redirected to the GWLB (via route table modifications in the VPC).
3. GWLB distributes traffic across security appliances (e.g., firewall EC2 instances).
4. Security appliances analyze the traffic and decide to allow or drop it.
5. Allowed traffic is sent back to the GWLB, which forwards it to the application.
6. Application receives traffic transparently – unaware of the security checks.