Alteon Application Switch Operating System Application Guide
Global Server Load Balancing
708
Document
ID:
RDWR-ALOS-V2900_AG1302
3. The Example Inc.'s San Jose DNS tells the local DNS to query the Alteon with GSLB software as
the authoritative name server for "www.example.com."
4. The San Jose Alteon responds to the DNS request, listing the IP address with the current best
service.
Each Alteon with GSLB software is capable of responding to the client's name resolution request.
Since each Alteon regularly checks and communicates health and performance information with
its peers, either Alteon can determine which sites are best able to serve the client's Web access
needs. It can respond with a list of IP addresses for the Example Inc.'s distributed sites, which
are prioritized by performance, geography, and other criteria.
In this case, the San Jose Alteon knows that Example Inc. Denver currently provides better
service, and lists Example Inc. Denver's virtual server IP address first when responding to the
DNS request.
5. The client connects to Example Inc. Denver for the best service.
The client's Web browser uses the IP address information obtained from the DNS request to
open a connection to the best available site. The IP addresses represent virtual servers at any
site, which are locally load balanced according to regular SLB configuration.
If the site serving the client HTTP content suddenly experiences a failure (no healthy real
servers) or becomes overloaded with traffic (all real servers reach their maximum connection
limit), Alteon issues an HTTP redirect and transparently causes the client to connect to another
peer site.
The end result is that the client gets quick, reliable service with no latency and no special client-
side configuration.
GSLB Metrics
This section describes all GSLB metrics as governed by DSSP. All metrics can be prioritized for
selection order, and can be weighted on a per site basis. This section includes the following sub-
sections:
•
•
•
GSLB Availability Persistence, page 710
•
GSLB Client Proximity Metric, page 711
For details on the configuration parameters of GSLB metrics, see the
/cfg/slb/gslb/rule
menu
and the command descriptions in the Alteon Application Switch Operating System Command
Reference.
The following is a list of all GSLB metrics:
•
Session utilization capacity threshold—Causes the GSLB-enabled Alteon to not select the
server when the session utilization of the server goes above the threshold. The session
utilization is the percentage of sessions used over total sessions that results in normalized
sessions between servers. When the server is not available, the session utilization is 100%. This
is a threshold metric and it overwrites all other metrics. This metric requires remote site
updates.
•
CPU utilization capacity threshold—Causes the GSLB-enabled Alteon to not select the
server when the CPU utilization of the site with the server goes above the threshold. CPU
utilization is the highest CPU utilization for periods of up to 64 seconds among SPs. This is a
threshold metric and overwrites all other metrics.This metric requires remote site updates.
•
Session available capacity threshold—Does not select the server when the number of
available sessions on the server falls below the threshold. When the server is not available, the
session available is 0. This is a threshold metric and it overwrites all other metrics. This metric
requires remote site updates.
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