ALB vs NLB vs API Gateway — A Story of Three Gatekeepers (And How to Choose the Right One)

Let me explain this in a way I wish someone had explained it to me earlier.

Imagine your application is a large corporate office building.

Every day, thousands of people (requests) arrive:

• Some are customers
• Some are internal employees
• Some are delivery agents
• Some… you don’t even trust

Now, you don’t let everyone walk in the same way, right?

👉 You hire different types of gatekeepers.

In AWS, those gatekeepers are:

• ALB (Application Load Balancer)
• NLB (Network Load Balancer)
• API Gateway

And choosing the wrong one is like putting a security guard where you needed a receptionist… or worse, a receptionist where you needed armed security.

Meet the 3 Gatekeepers

1. ALB — The Smart Receptionist

This is the person at the front desk who actually understands what visitors are saying.

You walk in and say:

“I’m here for the finance team.”

She replies:

“Second floor, left side.”

Another person says:

“I need tech support.”

She routes them somewhere else.

That’s exactly what ALB does.

It understands:

• URLs (/api, /login)
• Domains (app.company.com, admin.company.com)
• Headers and rules

Real Scenario

You built a system:

• / → Frontend (React)
• /api → Backend (Node.js)
• /admin → Admin panel

ALB routes traffic based on what the request is asking for.

When ALB is your best friend

Use ALB when:

• You’re building web apps
• You have multiple services behind one URL
• You want clean routing without complexity

When ALB will disappoint you

• Ultra-low latency systems
• Non-HTTP traffic (like raw TCP/UDP)

2. NLB — The Silent Security Guard

Now imagine a different kind of guard.

He doesn’t ask questions. He doesn’t care who you are. He just checks your pass and lets you in FAST.

No conversation. No delay.

That’s NLB.

It works at a lower level and focuses on:

• Speed
• Performance
• Stability

Real Scenario

You’re building:

• A trading platform
• A gaming backend
• A real-time chat server

Here, every millisecond matters.

You don’t want a “smart receptionist” slowing things down.

You want fast pass-through traffic.

When NLB is the right choice

Use NLB when:

• You need extreme performance
• You deal with TCP/UDP traffic
• You want static IPs
• You care about low latency over intelligence

When NLB is a bad idea

• When you need routing like /api vs /admin
• When you want HTTP-level features

NLB is powerful, but not smart

3. API Gateway — The Strict Security Manager

Now imagine someone even more powerful.

This person doesn’t just guide or allow entry… They verify identity, enforce rules, and monitor everything.

They might say:

• “Show your ID”
• “You’ve made too many requests today”
• “You are not authorized”

That’s API Gateway.

It’s not just routing — it’s control + security + governance

Real Scenario

You’re building:

• A mobile app backend
• A public API
• A serverless system using Lambda

You need:

• Authentication (JWT, Cognito)
• Rate limiting
• Request validation

API Gateway becomes your frontline defense

When API Gateway shines

Use API Gateway when:

• You’re exposing APIs to external users
• You need security & throttling
• You’re working with Lambda / serverless
• You want managed API infrastructure

When it’s overkill

• Simple internal routing
• High-volume internal traffic (can get expensive)

Sometimes people use API Gateway everywhere… and regret the bill later.

️ The Real Difference (No Jargon)

Let’s simplify this brutally:

• ALB → “Let me understand your request and route you correctly”
• NLB → “I don’t care, just go through FAST”
• API Gateway → “Who are you? Are you allowed? Now proceed”

A Real Architecture (How Pros Use Them)

In real-world systems, they’re not competitors — they’re teammates.

Example:

• CloudFront → Handles global traffic
• API Gateway → Handles external APIs securely
• ALB → Routes internal microservices
• NLB → Handles high-performance backend systems

The best architects don’t pick one… They combine them smartly

The 3 Questions That Will Save You

Whenever you’re confused, just ask:

1️⃣ Do I need smart routing (URLs, paths)?

👉 Use ALB

2️⃣ Do I need raw speed and performance?

👉 Use NLB

3️⃣ Do I need security, throttling, and API control?

👉 Use API Gateway

The Lesson I Learned (The Hard Way)

Early in my career, I used: ALB for everything

It worked… until:

• Costs increased
• Performance dropped
• Security became complex

That’s when I realized:

AWS doesn’t give you multiple services to confuse you It gives you options to design better systems

Final Thought

Choosing between ALB, NLB, and API Gateway is not about:

“Which one is best?”

It’s about:

“Which one fits this specific problem?”

Once you start thinking this way, you stop building just working systems…

…and start building well-architected systems.