# Classic Load Balancer (CLB)

## Overview

* It **makes routing decisions at either the transport layer (TCP/SSL) or the application layer (HTTP/HTTPS)**.<br>
* It **requires a fixed relationship between the load balancer port and the container instance port**.

## Listeners

* To start using using CLBs, you **must configure one or more listeners**.<br>

* **Listener:**

  * **A process that checks for connection requests**.
  * It is configured with a protocol and a port for front-end (client to load balancer) connections, and a protocol and a port for back-end (load balancer to back-end instance) connections.

* It **supports the following protocols:**
  * **HTTP**
  * **HTTPS (secure HTTP)**
  * **TCP**
  * **SSL (secure TCP)**