The difference between public and private Server Load Balancers (SLBs) is that private SLBs connect to their backend ECS instances using the private network (Intranet) while public SLBs connect to their backend ECS instances using the public network (Internet). This is true according to the Alibaba Cloud documentation on SLB1. Public SLBs are used to distribute traffic from the Internet to ECS instances, while private SLBs are used to distribute traffic within a VPC or a classic network2. References: 1: Server Load Balancer - Alibaba Cloud Documentation Center 2: Create a Server Load Balancer instance - Server Load Balancer - Alibaba Cloud Documentation Center