ALB vs NLB decision in AWS - Visual Side-by-Side Comparison

Process Flow - ALB vs NLB decision

Start: Incoming Client Request

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Choose Load Balancer Type

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Application Load Balancer

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Inspect HTTP/HTTPS

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End Decision

This flow shows how a client request is routed through either an Application Load Balancer (ALB) or a Network Load Balancer (NLB) based on protocol and use case.

Execution Sample

AWS

Client sends HTTPS request
Load Balancer inspects request
If HTTP/HTTPS -> ALB routes by URL
If TCP/UDP -> NLB routes by IP/port

This example shows how the load balancer type is chosen based on the incoming request protocol and how it routes traffic accordingly.

Process Table

Step	Incoming Request Protocol	Load Balancer Type Chosen	Routing Method	Use Case
1	HTTPS	ALB	Route by URL, Host, Headers	Web apps, microservices
2	TCP	NLB	Route by IP, Port	Extreme performance, static IP
3	UDP	NLB	Route by IP, Port	Low latency, millions of connections
4	HTTP	ALB	Route by URL, Host, Headers	Supports WebSockets, HTTP/2
5	Unknown Protocol	None	No routing	Request rejected or error

💡 Execution stops when request protocol is identified and routed or rejected if unsupported.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
Incoming Request Protocol	None	HTTPS	TCP	UDP	HTTP	Unknown
Load Balancer Type	None	ALB	NLB	NLB	ALB	None
Routing Method	None	URL/Host/Headers	IP/Port	IP/Port	URL/Host/Headers	None
Use Case	None	Web apps	Performance	Low latency	WebSockets	Rejected

Key Moments - 3 Insights

Why does ALB route based on URL and headers but NLB routes based on IP and port?

ALB works at the application layer (HTTP/HTTPS) so it can inspect URL and headers (see execution_table rows 1 and 4). NLB works at the transport layer (TCP/UDP) and routes by IP and port without inspecting content (rows 2 and 3).

What happens if the incoming request uses an unsupported protocol?

The load balancer cannot route the request, so it is rejected or causes an error (see execution_table row 5). This is why protocol detection is critical.

Why choose NLB for extreme performance and static IPs?

NLB operates at a lower network layer, handling millions of connections with very low latency and supports static IP addresses (rows 2 and 3), making it ideal for high-performance needs.

Visual Quiz - 3 Questions

Look at the execution_table, what load balancer type is chosen for an HTTPS request at step 1?

A NLB

B ALB

C None

D Both ALB and NLB

💡 Hint

Check the 'Load Balancer Type Chosen' column in execution_table row 1.

At which step does the load balancer reject the request due to unsupported protocol?

A Step 2

B Step 3

C Step 5

D Step 4

💡 Hint

Look for 'No routing' or 'Rejected' in the 'Routing Method' and 'Use Case' columns.

If the incoming request protocol changes from TCP to HTTP, how does the routing method change according to the execution_table?

A From IP/Port to URL/Host/Headers

B From URL/Host/Headers to IP/Port

C No change in routing method

D Routing method becomes None

💡 Hint

Compare routing methods in rows 2 (TCP) and 4 (HTTP) of the execution_table.

Concept Snapshot

ALB vs NLB Decision:
- ALB handles HTTP/HTTPS at app layer, routes by URL, headers
- NLB handles TCP/UDP at network layer, routes by IP and port
- Choose ALB for web apps, microservices, WebSockets
- Choose NLB for high performance, static IP, millions of connections
- Unsupported protocols cause request rejection

Full Transcript

This visual execution shows how AWS load balancers decide routing based on incoming request protocols. When a client sends a request, the system checks the protocol. If it is HTTP or HTTPS, the Application Load Balancer (ALB) is chosen. ALB routes traffic by inspecting URL, host, and headers, supporting web applications and microservices. If the protocol is TCP or UDP, the Network Load Balancer (NLB) is chosen. NLB routes traffic by IP address and port, providing high performance and static IP support. If the protocol is unsupported, the request is rejected. Variables like Incoming Request Protocol, Load Balancer Type, Routing Method, and Use Case change step-by-step as the request is processed. Key moments clarify why ALB and NLB route differently and what happens with unsupported protocols. The quiz tests understanding of load balancer choice and routing methods based on protocol.