AWS offers multiple load-balancing solutions tailored to different use cases within the Elastic Load Balancing (ELB) service. The two primary types are the Application Load Balancer (ALB) and the Network Load Balancer (NLB). Below is a detailed comparison of ALB and NLB, highlighting their features, use cases, and differences.

Key Features:

  1. Layer 7 Load Balancing:
    • Operates at the application layer (OSI layer 7), making it capable of routing HTTP/HTTPS traffic.
    • Supports advanced routing features such as host-based, path-based, and query string-based routing.
  2. Content-Based Routing:
    • Can route requests to different target groups based on the content of the request, allowing for more granular control over traffic distribution.
  3. SSL Termination:
    • Supports SSL/TLS termination, offloading the decryption/encryption work from your backend instances.
  4. WebSockets and HTTP/2:
    • Supports WebSocket and HTTP/2, making it suitable for modern web applications requiring persistent connections and better performance.
  5. WAF Integration:
    • Can integrate with AWS Web Application Firewall (WAF) to protect your web applications from common web exploits.
  6. Sticky Sessions:
    • Supports session stickiness (also known as session affinity) based on cookies, allowing a client to be bound to a specific target.

Use Cases:

  • Ideal for web applications needing advanced routing capabilities and content-based routing.
  • Suitable for microservices architectures, where different services might require different routing rules.
  • WebSocket applications and applications requiring HTTP/2 support.
  • Applications needing SSL termination and integration with WAF for enhanced security.

Key Features:

  1. Layer 4 Load Balancing:
    • Operates at the transport layer (OSI layer 4), handling TCP, UDP, and TLS traffic.
    • Designed for extreme performance, capable of handling millions of requests per second with ultra-low latency.
  2. Static IP Addresses:
    • Provides a static IP address for the load balancer, which can be useful for whitelisting and consistent endpoint references.
  3. Preserve Source IP:
    • Preserves the client source IP address, which is essential for applications needing to know the original IP address of the client.
  4. TLS Termination:
    • Can offload the TLS termination process from your backend instances, similar to ALB but at the transport layer.
  5. Zonal Isolation:
    • Provides high availability across multiple Availability Zones and can route traffic to healthy targets within a specific zone, ensuring robustness.

Use Cases:

  • Best suited for high-performance, latency-sensitive applications requiring extreme scalability.
  • Applications needing to handle non-HTTP/S traffic, such as TCP and UDP.
  • Use cases where preserving the source IP address is critical for the application logic.
  • Ideal for microservices requiring simple, fast, and reliable load balancing at the network layer.
Feature Application Load Balancer (ALB) Network Load Balancer (NLB)
Layer Layer 7 (Application Layer) Layer 4 (Transport Layer)
Protocols HTTP, HTTPS, WebSocket TCP, UDP, TLS
Routing Advanced routing based on URL, host, etc. Basic routing based on IP and port
SSL/TLS Termination Yes Yes
Static IP No Yes
Source IP Preservation No Yes
Performance Suitable for web traffic Ultra-low latency, high throughput
WebSocket and HTTP/2 Support Yes No
WAF Integration Yes No
Use Case Examples Web applications, microservices, APIs High-performance applications, gaming, IoT

Choosing between ALB and NLB depends on your specific application requirements:

  • Use ALB if you need advanced routing capabilities, support for modern web protocols (HTTP/2, WebSockets), SSL termination, and integration with WAF for web applications.
  • Use NLB if you need high performance, low latency, support for TCP/UDP traffic, static IP addresses, and the ability to preserve the client source IP address.

By understanding the strengths and use cases of each load balancer, you can make an informed decision that best suits your application’s architecture and performance requirements.

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