Classic Load Balancer (CLB)

Overview

The Classic Load Balancer (CLB) provides basic load balancing across multiple Amazon EC2 instances and operates at both the request and connection levels. It operates at layer 4 and layer 7. It supports the following protocols:

  • TCP
  • SSL
  • HTTP
  • HTTPS

Limitation

CLB does not support HTTP/2.

It integrates with Auto Scaling, CloudWatch, CloudTrail, and Route 53.

Load balancers can listen on the following ports:

  • [EC2-VPC] 1-65535
  • [EC2-Classic] 25, 80, 443, 465, 587, 1024-65535

CLBs do not have predefined IPv4 addresses but are resolved using a DNS name. However, they do support domain zone apex records, e.g., example.com. IPv4 and IPv6 are supported, but only IPv4 is supported within a VPC. It also provides SSL termination and processing.

Limitation

CLBs do not support Elastic IPs.

CLBs can work both internally and as Internet-facing. The diagram below shows how multiple CLBs can be used.

Level up your interview prep. Join Educative to access 80+ hands-on prep courses.