When it comes to managing and distributing incoming traffic across your compute resources, load balancing is an essential component of modern cloud architectures. AWS offers two powerful load balancing services: the Application Load Balancer (ALB) and the Network Load Balancer (NLB). While both services aim to optimize resource utilization and ensure high availability, they differ in their functionality and use cases. In this article, we’ll demystify the choice between ALB vs NLB, empowering you to make an informed decision for your application’s needs.

Table of Content

Introduction

An ALB routes traffic sequentially using the round-robin algorithm by default. On the other hand, an NLB employs a flow hash algorithm to route traffic in a predefined way to designated targets. ALB is focused on managing HTTP and HTTPS traffic, whereas NLB covers TCP, UDP, and TLS communication. Because the ALB runs on layer 7, each incoming HTTP request is examined in detail. On the other hand, the NLB operates on layer 4. Forwarding the incoming TCP or UDP connection to a target is all that matters to the NLB. For example, the NLB does not examine an incoming HTTP request.

The Application Load Balancer (ALB)

The ALB operates at the application layer (Layer 7) of the OSI model, allowing it to inspect and route traffic based on the content of the request. This powerful capability enables advanced features such as content-based routing, URL rewriting, and WebSocket support.

One of the key strengths of the ALB is its ability to handle HTTP/HTTPS traffic intelligently. It can route requests to different targets (e.g., EC2 instances, containers) based on the URL path or host-based routing rules. This flexibility makes ALBs an excellent choice for web applications, microservices architectures, and APIs that require granular routing and traffic management.

Additionally, ALBs can offload SSL/TLS decryption, reducing the computational load on your application servers and improving overall performance. This feature is particularly valuable for applications that handle a significant amount of encrypted traffic.

The Network Load Balancer (NLB)

In contrast, the NLB operates at the transport layer (Layer 4) of the OSI model, making it suitable for load balancing TCP, UDP, or TCP/UDP traffic. While it cannot inspect the content of the requests like the ALB, the NLB excels in scenarios where high performance and low latency are paramount.

NLBs are ideal for load balancing non-HTTP traffic, such as database connections, gaming servers, or other TCP/UDP-based applications. They provide a simple and efficient way to distribute traffic across multiple targets, ensuring optimal resource utilization and high availability.

Additionally, NLBs can be used to load balance HTTP/HTTPS traffic when advanced application-level routing features are not required. In such cases, the NLB offers a lightweight and high-performance solution, particularly beneficial for applications with stringent latency requirements.

ALB vs NLB: A Comparison

Comparing the features of Application Load Balancer (ALB) and Network Load Balancer (NLB):

This table highlights the key differences between ALB and NLB in terms of their operating layers, traffic types, routing capabilities, content inspection, SSL/TLS termination, WebSocket support, connection multiplexing, advanced routing features, metrics, latency characteristics, and typical use cases.

The table can help you quickly grasp the distinct features and functionalities of each load balancer, enabling you to make an informed decision based on your application’s requirements and workload characteristics.

When To Choose?

Choosing Between ALB and NLB The choice between ALB and NLB primarily depends on the type of traffic your application handles and the routing requirements you have. Here’s a simple decision-making guide:

Choose an Application Load Balancer (ALB) if:

• Your application primarily handles HTTP/HTTPS traffic.
• You require advanced routing features like content-based routing, URL rewriting, or WebSocket support.
• You need to offload SSL/TLS decryption from your application servers.
• Your application has a microservices architecture or requires granular routing rules.

Choose a Network Load Balancer (NLB) if:

• Your application handles non-HTTP traffic (e.g., TCP, UDP, or TCP/UDP).
• You need to load balance database connections, gaming servers, or other TCP/UDP-based applications.
• You require high performance and low latency for your load balancing needs.
• You need to load balance HTTP/HTTPS traffic but don’t require advanced routing features.

In general, the Network Load Balancer (NLB) is better equipped to handle spiky traffic due to its efficient connection handling, unlimited connection multiplexing, lack of content inspection overhead, and seamless scaling across multiple Availability Zones. The Application Load Balancer (ALB), while powerful for application-level routing and content manipulation, may face scalability challenges and higher overhead during sudden traffic spikes due to its connection termination and content inspection processes.

However, it’s worth noting that both ALB and NLB can be configured with sufficient capacity and autoscaling capabilities to handle anticipated traffic spikes effectively. The choice between the two should also consider other factors, such as the type of traffic, routing requirements, and overall application architecture.

Summary

In conclusion, the choice between an Application Load Balancer (ALB) and a Network Load Balancer (NLB) depends on the nature of your application’s traffic and the specific routing requirements you have. By understanding the capabilities and use cases of each load balancer, you can make an informed decision that optimizes resource utilization, ensures high availability, and aligns with your application’s architecture and performance needs.

You might need to combine both load balancers to meet your application’s requirements. For example, you could use an NLB to handle high-performance TCP traffic and an ALB to manage HTTP/HTTPS traffic with advanced routing rules.

FAQs:

Q1. Can an ALB handle non-HTTP traffic?

No, the Application Load Balancer is designed specifically to handle HTTP and HTTPS traffic. If you need to load balance non-HTTP traffic, such as TCP, UDP, or TCP/UDP, you should use a Network Load Balancer.

Q2. Is it possible to migrate from an ALB to an NLB or vice versa?

Yes, it is possible to migrate from an ALB to an NLB or vice versa. However, the migration process may require changes to your application’s configuration and target group setup, as the routing rules and capabilities differ between the two load balancers.

Q3. Can an NLB offload SSL/TLS decryption?

No, the Network Load Balancer operates at the transport layer and cannot inspect or modify the content of the requests. If you need to offload SSL/TLS decryption, you should use an Application Load Balancer.

Q4. How do ALBs and NLBs handle high availability and fault tolerance?

Both ALBs and NLBs are designed to be highly available and fault-tolerant. They automatically distribute traffic across multiple Availability Zones (AZs) and handle failover scenarios seamlessly. Additionally, you can configure health checks to monitor the health of your targets and automatically route traffic away from unhealthy instances.

Q5. Can I use both an ALB and an NLB in the same application?

Yes, it is possible to use both an ALB and an NLB in the same application architecture. This approach can be beneficial when you have different types of traffic that require different load balancing capabilities. For example, you could use an NLB for high-performance TCP traffic and an ALB for HTTP/HTTPS traffic with advanced routing requirements.

Q6. How do ALBs and NLBs handle security and compliance?

Both ALBs and NLBs are designed with security in mind and offer various features to ensure compliance with industry standards and best practices. For example, you can configure SSL/TLS termination, integrate with AWS WAF (Web Application Firewall), and leverage AWS PrivateLink for secure communication between your resources.

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