ALB vs NLB decision in AWS - When to Use Which

The Big Idea

What if your website could handle millions of visitors without you lifting a finger to direct traffic?

The Scenario

Imagine you have a website and an app that need to share traffic smoothly. You try to direct users manually to different servers by changing settings one by one.

It's like standing at a busy intersection and manually telling each car where to go.

The Problem

This manual way is slow and confusing. You can easily send users to the wrong place or overload one server while others sit idle.

Fixing mistakes takes time and can cause your site to crash or slow down.

The Solution

Using Application Load Balancer (ALB) or Network Load Balancer (NLB) automates this traffic direction smartly.

They act like traffic controllers that quickly and correctly send users to the best server based on the type of request or network speed.

Before vs After

✗ Before

Change DNS records manually for each server
Monitor traffic and adjust routes by hand

✓ After

Use ALB for smart routing based on web requests
Use NLB for fast routing of network traffic

What It Enables

You can handle millions of users smoothly without worrying about traffic jams or server crashes.

Real Life Example

A popular online store uses ALB to send customers to different servers based on the page they want, like product pages or checkout.

At the same time, it uses NLB to handle fast connections for payment processing securely and reliably.

Key Takeaways

Manual traffic management is slow and error-prone.

ALB and NLB automate and optimize traffic routing.

Choosing the right load balancer improves user experience and reliability.

Practice

1. Which AWS load balancer should you choose if you want to route HTTP requests based on URL paths?

easy

A. Gateway Load Balancer

B. Network Load Balancer (NLB)

C. Classic Load Balancer

D. Application Load Balancer (ALB)

Solution

1. Step 1: Understand ALB routing capabilities

   ALB can route HTTP/HTTPS traffic based on content like URL paths or host headers.

2. Step 2: Compare with NLB capabilities

   NLB routes at the network level and does not inspect HTTP content for routing.

3. Final Answer:

   Application Load Balancer (ALB) -> Option D

4. Quick Check:

   Content-based routing = ALB [OK]

Hint: Use ALB for HTTP content routing, not NLB [OK]

Common Mistakes:

• Choosing NLB for HTTP content routing
• Confusing Classic Load Balancer with ALB
• Assuming NLB can inspect HTTP headers

2. Which protocol is primarily supported by Network Load Balancer (NLB) for fast, low-latency traffic?

easy

A. TCP/UDP

B. FTP

C. HTTP/HTTPS

D. SMTP

Solution

1. Step 1: Identify NLB protocol support

   NLB is designed to handle TCP and UDP traffic for fast, low-latency connections.

2. Step 2: Exclude HTTP/HTTPS protocols

   HTTP/HTTPS are application layer protocols handled by ALB, not NLB.

3. Final Answer:

   TCP/UDP -> Option A

4. Quick Check:

   NLB = TCP/UDP traffic [OK]

Hint: NLB handles TCP/UDP, ALB handles HTTP/HTTPS [OK]

Common Mistakes:

• Selecting HTTP/HTTPS for NLB
• Confusing FTP or SMTP as NLB protocols
• Assuming NLB supports application layer protocols

3. You have a web application that requires routing requests based on hostnames and needs SSL termination. Which load balancer will correctly handle this?

medium

A. Network Load Balancer (NLB)

B. Gateway Load Balancer

C. Application Load Balancer (ALB)

D. Classic Load Balancer

Solution

1. Step 1: Check hostname-based routing support

   ALB supports routing based on hostnames, which is needed here.

2. Step 2: Confirm SSL termination capability

   ALB can terminate SSL connections, simplifying certificate management.

3. Final Answer:

   Application Load Balancer (ALB) -> Option C

4. Quick Check:

   Hostname routing + SSL termination = ALB [OK]

Hint: SSL termination and hostname routing need ALB [OK]

Common Mistakes:

• Choosing NLB which lacks hostname routing
• Assuming Classic Load Balancer supports advanced routing
• Confusing Gateway Load Balancer with ALB

4. A developer configured a Network Load Balancer to route HTTP traffic and expects it to inspect URL paths for routing. Why is this setup incorrect?

medium

A. NLB does not support TCP traffic

B. NLB cannot inspect HTTP content for routing decisions

C. NLB requires SSL certificates for HTTP routing

D. NLB only supports routing based on IP addresses

Solution

1. Step 1: Understand NLB routing capabilities

   NLB operates at the network layer and cannot inspect HTTP content like URL paths.

2. Step 2: Identify why HTTP content inspection fails

   Routing based on URL paths requires application layer inspection, which only ALB supports.

3. Final Answer:

   NLB cannot inspect HTTP content for routing decisions -> Option B

4. Quick Check:

   NLB lacks HTTP content inspection [OK]

Hint: NLB works at network layer, no HTTP content routing [OK]

Common Mistakes:

• Thinking NLB supports HTTP path routing
• Confusing TCP support with HTTP inspection
• Assuming SSL certs fix routing issues

5. You need to design a system that handles millions of TCP connections with very low latency and also routes HTTP requests based on URL paths. What is the best load balancer setup?

hard

A. Use NLB for TCP connections and ALB for HTTP routing

B. Use only an Application Load Balancer (ALB) for all traffic

C. Use only a Network Load Balancer (NLB) for all traffic

D. Use Classic Load Balancer for both TCP and HTTP traffic

Solution

1. Step 1: Identify requirements for TCP and HTTP traffic

   Millions of TCP connections need low latency, best handled by NLB. HTTP routing by URL paths requires ALB.

2. Step 2: Combine load balancers for best performance

   Use NLB for TCP traffic and ALB for HTTP traffic to meet both needs efficiently.

3. Final Answer:

   Use NLB for TCP connections and ALB for HTTP routing -> Option A

4. Quick Check:

   TCP low latency + HTTP routing = NLB + ALB [OK]

Hint: Combine NLB for TCP and ALB for HTTP routing [OK]

Common Mistakes:

• Using only ALB for TCP traffic causing latency
• Using only NLB missing HTTP routing features
• Choosing Classic Load Balancer for modern needs