The Edge SWG (ProxySG) can load balance servers in a service group, a list of ICAP servers, or in a Malware Scanning.
The Edge SWG (ProxySG) performs load balancing via round-robin without giving any ICAP server preference by default. If the legacy feature (before 7.x ) Malware Scanning is enabled, the ICAP servers also use round-robin. All the ICAP servers have a weight of "1", so the ProxySG evenly forwards requests sequentially to servers as defined within the ICAP server list, ICAP servers in the service group, or the Malware Scanning list. Here is more information on Service Groups load balancing. The default behavior can be changed when using Service Groups by applying different weights to ICAP servers. However, the default behavior cannot be changed for ICAP servers in Malware Scanning.