Site adx device’s administrative preference, The least response selection – Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) User Manual
Page 21
Brocade Virtual ADX Global Server Load Balancing Guide
11
53-1003245-01
Global Server Load Balancing overview
1
Site ADX device’s administrative preference
The administrative preference is an optional metric. This metric is a numeric preference value from
0 to 255 that you assign to each site ADX device, to select that ADX device if the previous metrics
do not result in selection of a best site. The GSLB policy prefers the site ADX device with the highest
administrative preference.
The administrative preference allows you to do the following:
•
You can temporarily change the preference of a site to accommodate changing network
conditions. For example, if sites are offering proxy content service, the link between a site proxy
server farm and the content origin may be highly congested, making that site less desirable.
This factor is not visible to the ADX devices and thus cannot be reflected in the other GSLB
metrics.
•
You can temporarily disqualify a site ADX device from being selected, without otherwise
changing the site’s configuration or the GSLB Brocade Virtual ADX’s configuration. For
example, you can perform maintenance on the site ADX device without making network
changes. In this case, set the administrative preference to 0.
•
You can bias a GSLB Brocade Virtual ADX that is also configured as a site ADX device (for
locally configured VIPs) to always favor itself as the best site. In this case, assign an
administrative preference of 255 to the site for the GSLB Brocade Virtual ADX itself, and assign
a lower administrative distance to the other site ADX devices, or use the default (128) for those
sites.
The administrative preference is disabled by default, which means it is not included as one of the
GSLB metrics. When you enable this metric, the default administrative preference for sites is 128.
You can change the preference on an individual site basis. To change a site’s preference, refer to
The least response selection
If multiple sites still compare equally based on all the metrics above, the GSLB Brocade Virtual ADX
selects the site that it has selected least often before. For example, if the GSLB Brocade Virtual
ADX has selected Site 1 and placed its IP address on top in 40% of the DNS replies, but has
selected Site 2 60% of the time, then in this instance the GSLB Brocade Virtual ADX selects Site 10.
To display the response selection percentages for the sites you have configured, use the show gslb
dns zone command. Refer to
“Displaying DNS zone and hosts”
This metric is a tie-breaker in case multiple addresses pass through all the above comparisons
without one address emerging as the best choice. If this occurs, the address of the site that has
been selected least often in previous DNS responses is selected.
Least Response Selection is enabled by default. You can disable the metric only by enabling the
Round Robin Selection metric to act as the tie breaker instead. See the following section.