Symptoms
RDS hosts are not well load balanced.
Purpose
To highlight a change in behaviour with load-index based load balancing in Horizon 8.4
Cause
Load-index-based load balancing in Horizon 8.4 has been modified to mitigate flooding the least loaded RDS host with all the start sessions during a logon storm.The updated algorithm now classifies RDS hosts into three distinct groups, with the first bucket consisting of RDS hosts that have a load index below 75.This modification ensures that session requests are evenly distributed among all the RDS hosts in the first bucket to prevent overwhelming the least loaded RDS host during a logon storm.The Default load index threshold which is 75, is too high to accommodate multiple RDS agents in the first bucket. As a result, every RDS agent in the first bucket will be treated fairly when distributing start session requests.
Resolution
Decreasing the default load index threshold to a lower value (recommendation is 20) will ensure only the servers with the lower load(less than 20) will be selected for the first bucket. This will guarantee that start session distribution is exclusively handled by these least-loaded servers.If we don't have a minimum of 4 RDS agents in the first bucket (configurable via pae-MinRDSServersInLBQueue, with a default value of 4), We gradually increase the load index threshold dynamically, until the minimum number of RDS agents is attainedTake an appropriate backup
Backup: Backup and Restore procedure for Horizon 7 environment (74875)Restore: Restore Procedure for Site Recovery with Machine Backups(76765)For additional options, please see Recovery scenarios for Horizon 8 environment (70906)
Change the default load Index threshold value to 20.1. Connect to the LDAP DB: A step-by-step procedure is documented here: Connecting to the View ADAM LDAP Database (2012377)2. Navigate to this location:
CN=Common,OU=Global,OU=Properties
3. set this attribute value pae-RDSLoadIndexThreshold to 20
Once set, allow some time for this to replicate across all Horizon Connection Servers, for additional details on replication, please see documentation: Horizon LDAP
