AWS Elastic Load Balancing Concepts
External
Internal
Overview
Load Balancer
A load balancer serves as the single point of contact for clients. The load balancer distributes incoming traffic across multiple targets, which actually know how to handle requests and provide responses. This increases the availability of the application. A load balancer can have one or more listeners.
Load Balancer Name
The name of a load balancer must be unique within the set of Application Load Balancers and Network Load Balancers for the region.
Listener
A listener is a process that checks for client connection requests, over a pre-configured protocol and port, and forwards requests to a target group. Rules can be defined for a listener that determine how the load balancer routes requests to the targets in one or more target groups. One listener is defined when the load balancer is created, and more listeners can be added at any time after that.
Listener Rule
There is a default listener rule.
Target Group
A target group routes requests to one or more registered targets, which can be EC2 instances, using a pre-configured TCP protocol and the port. A target can be registered with multiple target groups. A target group supports health checks: health checks are performed on all target registered to a target group that is specified on a listener rule for the load balancer.
Target
Target Type
Instance
The target is specified by the instance ID.
IP
The target type is specified by an IP address. The IP address can be specified from one of the following CIDR blocks:
- the subnets of the VPC for the target group.
- 10.0.0.0/8 (RFC 1918)
- 100.64.0.0/10 (RFC 6598)
- 172.16.0.0/12 (RFC 1918)
- 192.168.0.0/16 (RFC 1918)
Publicly routable IP addresses can't be specified.