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Example weighted load balancing configuration

Consider a cluster of three FortiGates with host names FGT_ha_1, FGT_ha_2, and FGT_ha_3 as shown below. This example describes how to configure weighted load balancing settings for CPU and memory usage for the cluster and then to configure HTTP and POP3 proxy weights to send most HTTP and POP3 proxy sessions to different cluster units.

Example HA weighted load balancing configuration

Connect to the cluster CLI and use the following command to set the CPU usage threshold weight to 30, low watermark to 60, and high watermark to 80. This command also sets the memory usage threshold weight to 10, low watermark to 60, and high watermark to 90.

config system ha

set mode a-a

set schedule weight-round-robin

set cpu-threshold 30 60 80

set memory-threshold 10 60 90


The static weights for the cluster units remain at the default values of 40. Since this command changes the mode to a-a and the schedule to weight-round-robin for the first time, the weight settings are synchronized to all cluster units.

As a result of this configuration, if the CPU usage of any cluster unit (for example, FGT_ha_1) reaches 80% the static weight for that cluster unit is reduced from 40 to 10 and only 10 of every 120 new sessions are load balanced to this cluster unit. If the memory usage of FGT_ha_1 also reaches 90% the static weight further reduces to 0 and no new sessions are load balanced to FGT_ha_1. Also, if the memory usage of 620_ha_2 reaches 90% the static weight of FGT_ha_2 reduces to 30 and 30 of every 120 new sessions are load balanced to FGT_ha_2.

Now that you have established the weight load balancing configuration for the entire cluster you can monitor the cluster to verify that processing gets distributed evenly to all cluster units. From the GUI you can go do System > HA > View HA Statistics and see the CPU usage, active sessions, memory usage and other statistics for all of the cluster units. If you notice that one cluster unit is more or less busy than others you can adjust the dynamic weights separately for each cluster unit.

For example, in some active-active clusters the primary unit may tend to be busier than other cluster units because in addition to processing sessions the primary unit also receives all packets sent to the cluster and performs load balancing to distribute the sessions to other cluster units. To reduce the load on the primary unit you could reduce the CPU and memory usage high watermark thresholds for the primary unit so that fewer sessions are distributed to the primary unit. You could also reduce the primary unit’s high watermark setting for the proxies to distribute more proxy sessions to other cluster units.

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This would only be useful if you are using device priorities and override settings to make sure the same unit always becomes the primary unit. See Controlling primary unit selection using device priority and override.

If the example cluster is configured for FGT_ha_2 to be the primary unit, connect to the FGT_ha_2’s CLI and enter the following command to set CPU usage, memory usage, and proxy usage high watermark thresholds lower.

config system ha

set cpu-threshold 30 60 70

set memory-threshold 30 60 70

set http-proxy-threshold 30 60 70

set ftp-proxy-threshold 30 60 70

set imap-proxy-threshold 30 60 70

set nntp-proxy-threshold 30 60 70

set pop3-proxy-threshold 30 60 70

set smtp-proxy-threshold 30 60 70


As a result, when any of these factors reaches 70% on the primary unit, fewer sessions will be processed by the primary unit, preventing the number of sessions being processed from rising.