How Gateway Load Balancer Enhances Traffic Security in AWS

Arjun had just mastered Application Load Balancers and Network Load Balancers. Things were smooth—until one day, his company’s security team gave him a new mission:

“We want every bit of traffic—before it hits any app—to pass through our firewall appliances. Can you set that up in AWS?”

Arjun knew this wasn’t something a regular ALB or NLB could do. That’s when he was introduced to a special kind of load balancer: Gateway Load Balancer (GWLB).

📦 The Problem

Before GWLB, routing traffic through custom firewalls or deep inspection systems was complicated:

Lots of manual routing
Fragile NAT rules
No easy scaling or fault tolerance

Now, GWLB changes everything.

📘 What Is a Gateway Load Balancer (GWLB)?

A Gateway Load Balancer (GWLB) lets you transparently insert third-party appliances (like firewalls or deep packet inspectors) into your network traffic flow—at scale and with high availability.

Think of it as a checkpoint in your VPC that all traffic must pass through, where it’s inspected, approved (or dropped), and then forwarded to your applications.

🛠️ How GWLB Works — Simple Flow

Here’s the process Arjun mapped out:

User traffic enters the VPC.
Instead of going directly to the app (like in ALB/NLB), it first goes to the Gateway Load Balancer.
GWLB forwards this traffic to a target group of firewall appliances (a set of special EC2 instances running security software like Firewall, IDS, IPS, Deep Packet Inspection tools).

✅ What Do These EC2 Instances (Appliances) Do?

Inspect every packet in the network traffic
(they can look at IP headers, payloads, suspicious patterns)
Block bad traffic (like malicious requests, viruses, or strange IPs)
Allow good traffic to pass through

🔁 What Happens Next?

If the traffic is safe → it’s sent back to the GWLB, which forwards it to your Application Load Balancer or app.
If it’s unsafe → the appliance drops the traffic, and it never reaches your app.

🧠 In simple terms:

Think of these EC2 instances like security guards at a checkpoint.
GWLB is the entry gate, and all cars (traffic) must go through the guards (firewall EC2s) before reaching the actual building (your app).

🌍 Where Does GWLB Fit in the OSI Model?

Unlike ALB (Layer 7) and NLB (Layer 4), GWLB operates at Layer 3 — the Network Layer.

It inspects IP packets.
Uses the GENEVE protocol (port 6081) to forward traffic between GWLB and appliances.

📘 SAA Tip: If you see "GENEVE protocol" or port 6081 mentioned, the answer is definitely Gateway Load Balancer.

🎯 The Goal

Arjun needed a setup where:

🛡️ All user traffic is inspected first
✅ Clean traffic is allowed through
❌ Malicious traffic is dropped
📲 Apps still work as normal—they don’t even know inspection happened

But the big question was:

“Where should I place the Gateway Load Balancer?”

🧭 Arjun’s Options

❌ Option 1: Internet → ALB → App

This was great for normal apps, but didn’t include any security layer.

❌ Option 2: Internet → Security Appliance → App

Too complex. Hard to scale. No fault tolerance.

✅ The Winning Architecture: GWLB → ALB → App

Arjun found the recommended pattern from AWS:

scssCopyEditInternet
   ↓
GWLB (in Security VPC)
   ↓
Firewall Appliances (EC2)
   ↓
ALB or NLB
   ↓
Backend App (EC2, ECS, Lambda)

Here’s how it worked:

All traffic hits GWLB first
This acts as a checkpoint.
GWLB sends traffic to a group of firewall EC2 instances
These appliances inspect every packet.
If the traffic is safe:
- ✅ It’s sent forward to an Application Load Balancer (ALB)
ALB then routes it smartly to:
- /login → Auth service
- /search → Search service
Finally, the user gets a response.
The application never even knows the traffic was inspected.

🧠 Bonus: GWLB Works Across VPCs

Arjun also learned that GWLB can sit in a central "security VPC".

Other VPCs (like dev, prod, staging) connect to GWLB using a special link called a Gateway Load Balancer Endpoint (GWLBe).

This meant:

🔐 One central firewall setup
🛠️ Easier management
⚖️ Auto-scaling appliances
🌍 Used across the entire AWS organization

📘 Final Takeaway for Arjun

“So I put the Gateway Load Balancer first, then let it send clean traffic to the ALB. That way, I get both security filtering and application routing—in one seamless flow.”

✅ Arjun’s Final Architecture:

javaCopyEditInternet
   ↓
Gateway Load Balancer (Layer 3)
   ↓
Firewall EC2 Appliances (Security VPC)
   ↓
Application Load Balancer (Layer 7)
   ↓
App Services (EC2, ECS, Lambda)

This gave Arjun:

✅ Transparent packet inspection
✅ Scalable firewalls
✅ Smart routing via ALB
✅ Peace of mind