Network Load Balancer - NLB

A Network Load Balancer (NLB) is a service that distributes network traffic at the transport layer (Layer 4 of the OSI model). Unlike the Application Load Balancer (ALB), which operates at the application layer (Layer 7), the NLB works at a lower level, primarily considering IP addresses and port numbers to distribute traffic.

Here are some features and functions of a Network Load Balancer:

1. Layer 4 Load Balancing: The NLB distributes network traffic based on IP addresses and port numbers. This type of load balancing is versatile, as it is independent of application protocols.

2. TCP and UDP Protocol Support: NLBs support both the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP), allowing them to handle traffic for a variety of applications.

3. Scalability: Similar to ALB, the NLB also supports application scaling by automatically adding new instances or resources and distributing network traffic accordingly.

4. Health Monitoring: The NLB continuously monitors the health of targets (servers or resources) to ensure that traffic is only directed to healthy targets.

5. Static IP Addresses and Port Mapping: NLBs can use static IP addresses and port mappings to ensure that incoming traffic is directed to the correct targets.

6. Fewer Application-Level Features: Compared to an ALB, an NLB provides fewer features at the application layer, as it primarily operates at the network level. However, it can provide basic protocol features such as TCP and UDP load balancing.

Network Load Balancers are commonly used in scenarios where traffic needs to be distributed at the transport layer without requiring specific application-level information. This makes them particularly suitable for protocols where simple forwarding based on IP addresses and ports is sufficient.