What is a Network Load Balancer in AWS?

A Network Load Balancer is one of the different types of Elastic Load Balancing options offered by AWS. It works at Layer 4 of the OSI Model

Elastic Load Balancing helps distributing incoming traffic across multiple targets such as Amazon EC2 instances, microservices, and containers in one or more Availability Zones. It offers the following options –

A Network Load Balancer is one of the different types of Elastic Load Balancing options offered by AWS.

It works at Layer 4 of the OSI Model – Transport Layer.

It offers a load balancing solution to distribute incoming TCP or UDP traffic across target groups. It can handle millions of requests per second.

For TCP traffic –

  • an NLB selects a target using a flow hash algorithm based on the protocol, source IP address, source port, destination IP address, destination port, and TCP sequence number.
  • Since the TCP connections from a client have different source ports and sequence numbers, they can be routed to different targets.
  • Each individual TCP connection is routed to a single target for the life of the connection.

For UDP traffic –

  • it selects a target using a flow hash algorithm based on the protocol, source IP address, source port, destination IP address, and destination port.
  • Since UDP flow has the same source and destination, it is consistently routed to a single target throughout its lifetime.

You can register instance IDs, IP Addresses or an Application Load Balancer as target groups to a Network Load Balancer. They have the following features –

  • If the target is an Instance ID, the source IP addresses of the clients are preserved and provided to the underlying applications.
  • If the target is an IP Address, the source IP addresses are the private IP addresses of the load balancer nodes and the client IP is not passed down.
  • If the target is an Application Load Balancer, the source IP addresses of the clients are preserved and provided.
Sriram Mannava
Sriram Mannava

I'm a full-stack developer and a software enthusiast who likes to play around with cloud and tech stack out of curiosity.

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