Question 1

What's the difference between an Application Load Balancer and a Network Load Balancer?

Accepted Answer

An Application Load Balancer (ALB) works at Layer 7 (HTTP/HTTPS). It can route based on content like URL paths, host headers, and HTTP methods, and it understands web concepts like cookies and redirects. A Network Load Balancer (NLB) works at Layer 4 (TCP/UDP/TLS). It’s optimized for very high performance and low latency, but it doesn’t do content-based routing because it doesn’t inspect HTTP requests.

Question 2

When should I use an Application Load Balancer?

Accepted Answer

Use an ALB when you’re serving HTTP/HTTPS applications and need features like path-based routing (e.g., /api vs /checkout), host-based routing (api.example.com vs www.example.com), TLS termination, WebSocket support, or tight integration with container and instance targets. It’s especially useful for microservices where different services share the same domain but use different routes.

Question 3

How much does an Application Load Balancer cost?

Accepted Answer

ALB pricing is usage-based. In AWS, you typically pay for (1) the time the load balancer runs and (2) capacity consumed, measured in Load Balancer Capacity Units (LCUs). LCUs are influenced by factors such as new connections per second, active connections, processed bytes, and rule evaluations. Costs increase with higher traffic volume, more complex routing rules, and more data processed. For exact rates, use the AWS pricing page and the AWS Pricing Calculator for your region and expected traffic.

Application Load Balancer

Definition

Real-World Example

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