A load balancer serves as the single point of contact for clients. Clients send requests to the load balancer, and the load balancer sends them to targets, such as EC2 instances, in one or more Availability Zones.
To configure your load balancer, you create Target Groups and then register targets with your target groups. Your load balancer is most effective if you ensure that each enabled Availability Zone has at least one registered target. You also create listeners to check for connection requests from clients and route requests from clients to the targets in your target groups.
Network Load Balancers support connections from clients over VPC peering, AWS managed VPN, AWS Direct Connect, and third-party VPN solutions.
Listeners for your Network Load Balancers:
A listener is a process that checks for connection requests, using the protocol and port that you configure. Before you start using your Network Load Balancer, you must add at least one listener. If your load balancer has no listeners, it can’t receive traffic from clients. The rule that you define for a listener determines how the load balancer routes requests to the targets that you register, such as EC2 instances.
Target groups for your Network Load Balancers:
Each target group is used to route requests to one or more registered targets. When you create a listener, you specify a target group for its default action. Traffic is forwarded to the target group specified in the listener rule. You can create different target groups for different types of requests. For example, create one target group for general requests and other target groups for requests to the microservices for your application.
You define health check settings for your load balancer on a per target group basis. Each target group uses the default health check settings, unless you override them when you create the target group or modify them later on. After you specify a target group in a rule for a listener, the load balancer continually monitors the health of all targets registered with the target group that are in an Availability Zone enabled for the load balancer. The load balancer routes requests to the registered targets that are healthy.