ServerIron ADX Global Server Load Balancing Guide 123
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Host-level policies for site selection 1
Enabling the Num-session metric
The capacity threshold specifies how close to the maximum session capacity the site
ServerIronADX (remote ServerIron ADX) can be and still be eligible as the best site for the client.
This mechanism provides a way to shift load away from a site before the site becomes congested.
The GSLB ServerIron ADX uses this metric when evaluating the sites in a DNS reply to choose the
best site.
To enable the num-session metric for a host-level policy, enter commands such as the following:
GSLB-ServerIronADX(config)# gslb-host-policy abc
GSLB-ServerIronADX(config-gslb-host-policy-abc)# num-session
Syntax: [no] num-session
Use the no form of the command to disable the Num-session metric.
Configuring the Num-session Tolerance
You can specify the percentage by which the number of available sessions on the site ServerIron
ADX can differ from the number of available sessions on another site ServerIron ADX and still be
considered an equally good site. To do this, enter commands such as the following:
GSLB-ServerIronADX(config)# gslb-host-policy abc
GSLB-ServerIronADX(config-gslb-host-policy-abc)# num-session tolerance 20
Syntax: [no] num-session tolerance <num>
The <num> parameter specifies the maximum percentage by which the session table utilization on
ServerIron ADXs at different sites can differ without the GSLB ServerIron ADX selecting one over the
other based on this metric. You can specify a tolerance from 0-100. The default is 10.
Enabling the Preference metric
To enable the Preference metric for a host-level policy, enter commands such as the following:
GSLB-ServerIronADX(config)# gslb-host-policy abc
GSLB-ServerIronADX(config-gslb-host-policy-abc)# preference
Syntax: [no] preference
Use the no form of the command to disable the Preference metric.
Enabling the Round-Robin Selection metric
The round robin selection metric is an alternative to the least response selection metric as the final
tie breaker. When you enable round robin selection, the GSLB ServerIron ADX automatically
disables the least response selection metric, and instead uses the round robin algorithm for GSLB
selection.
Use the round robin selection metric instead of the least response selection metric when you want
to prevent the GSLB ServerIron ADX from favoring new or recently recovered sites over previously
configured active sites.
The round robin selection metric is disabled by default. When you enable the metric, the software
automatically disables the least response selection metric, since they are mutually exclusive.
Likewise, if you disable the round robin selection metric, the software automatically re-enables the
least response selection metric.
To enable round robin selection for a host-level policy, enter commands such as the following:
GSLB-ServerIronADX(config)# gslb-host-policy abc
GSLB-ServerIronADX(config-gslb-host-policy-abc)# round-robin