Difference between ALB and NLB

Both Application Load Balancer (ALB) and Network Load Balancer (NLB) are load balancing solutions provided by Amazon Web Services (AWS) for distributing incoming traffic across multiple targets, but they operate at different layers of the OSI model and serve different use cases:

1. Layer of Operation:

   • Application Load Balancer (ALB) operates at Layer 7 (Application layer) of the OSI model. It is capable of routing traffic based on content of the HTTP/HTTPS requests, such as the URL, host, headers, and request method.
   • Network Load Balancer (NLB) operates at Layer 4 (Transport layer) of the OSI model. It routes traffic based on information in the TCP/UDP protocol headers, such as IP addresses and ports.

2. Use Cases:

   • ALB is typically used for applications that rely on HTTP and HTTPS traffic. It is ideal for load balancing HTTP/HTTPS web applications and provides features like path-based routing, host-based routing, and support for WebSocket and HTTP/2.
   • NLB is well-suited for applications that require high performance, low latency, and handling of millions of requests per second. It is commonly used for TCP and UDP-based traffic, such as handling TCP traffic for databases, gaming applications, and IoT applications.

3. Target Groups:

   • ALB routes traffic to target groups based on rules defined by the user. Target groups can include EC2 instances, IP addresses, Lambda functions, or containers.
   • NLB routes traffic to target groups, but unlike ALB, it forwards the original source IP of the client to the targets by default. This feature is especially useful for applications that require the client's IP address for processing requests.

4. Health Checks:

   • Both ALB and NLB support health checks to monitor the health of registered targets and route traffic only to healthy targets. However, NLB supports fewer health check options compared to ALB.

5. Pricing:

   • The pricing structure for ALB and NLB differs slightly based on factors like the number of load balancer instances, data processing, and cross-zone load balancing. Generally, NLB tends to have a slightly higher cost compared to ALB due to its performance-oriented features.

In summary, ALB and NLB are both powerful load balancing solutions provided by AWS, but they cater to different use cases and operate at different layers of the OSI model, allowing users to choose the one that best fits their specific application requirements.

Beyond their differences in the OSI layers they operate on, Application Load Balancer (ALB) and Network Load Balancer (NLB) have distinct practical use cases that align with their specific features and capabilities:

Application Load Balancer (ALB):

1. HTTP and HTTPS Load Balancing: ALB excels at load balancing HTTP and HTTPS traffic, making it suitable for web applications, APIs, and microservices architectures.
2. Path-Based Routing: ALB allows routing requests to different backend services based on the URL paths, enabling the hosting of multiple applications or APIs on a single ALB.
3. Host-Based Routing: With support for host-based routing, ALB can route requests to different backend services based on the hostnames specified in the HTTP request.
4. Containerized Workloads: ALB integrates well with containerized workloads on AWS, such as those managed by Amazon ECS or Kubernetes on Amazon EKS, providing dynamic and scalable load balancing for containerized applications.
5. WebSocket Support: ALB supports WebSocket protocol, making it suitable for real-time communication applications like chat applications, multiplayer gaming, and live streaming.

Network Load Balancer (NLB):

1. High-Performance Load Balancing: NLB is designed for high-performance, low-latency scenarios and is capable of handling millions of requests per second with minimal latency.
2. TCP and UDP Load Balancing: NLB is well-suited for TCP and UDP-based applications, making it suitable for applications like databases, gaming servers, IoT platforms, and custom protocols.
3. Static IP Address: NLB provides a static IP address that can be used as the entry point for applications requiring a fixed IP address, such as whitelisting for security or DNS routing.
4. Direct Server Return (DSR): NLB supports Direct Server Return, a feature that allows the backend servers to respond directly to the client's requests without routing the response back through the load balancer, reducing latency and load on the load balancer.
5. Preservation of Source IP Addresses: NLB forwards the original source IP addresses of the clients to the backend targets by default, which is important for applications that require the client's IP address for logging, security, or compliance purposes.

In summary, ALB and NLB cater to different use cases based on their features and capabilities, with ALB being more suitable for HTTP/HTTPS traffic and dynamic routing scenarios, while NLB excels in handling high-performance TCP/UDP traffic and scenarios where preserving the original client IP address is crucial.