To meet business requirements, a user requires that the backend server of an SLB instance...

Active/standby server groups are a feature of Server Load Balancer (SLB) that allows you to configure a primary ECS instance and a secondary ECS instance for the backend of an SLB instance1. When the primary instance is working properly, the traffic is only forwarded to the primary ECS. When the primary instance is down, traffic is switched to the standby instance1. This feature is supported by TCP and HTTPS listeners, but not by HTTP and UDP listeners1. TCP and HTTPS listeners support session persistence, which ensures that requests from the same client are always forwarded to the same backend server2. HTTP and UDP listeners do not support session persistence, and they use round-robin or weighted round-robin algorithms to distribute traffic among the backend servers2. References: 1: Create an active/standby server group 2: [Configure a listener]