HP Multi-Site Traffic Director sa9200 User Manual
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C H A P T E R 2
Metric Algorithms
11
method are enterprises that have identified the efficient
fulfillment of a specific type or types of traffic as being crucial to
their business goals.
•
Least Connections - The Least Connections method sends
requests to the site with fewest number of connections. This
method permits the most efficient management of requests that
are likely to require connections of long duration, such as FTP.
•
CPU Utilization of Local Load Balancer - This method directs
clients to the site whose load balancer has the lightest workload.
The benefit of this method is most evident when used with sites
performing processor-intensive Layer 7 load balancing.
Managing Unequal Site Servers
There is a “factor” command to determine a threshold factor in the
event of two unequal servers. (see config dns zones <zonename>
hostnames <hostname> siteservices <siteservicename> factor in
Chapter 6, “CLI Reference.”)
The SA9200 determines which IP address to return for a hostname,
based on the performance of the IP address and port at a site. The
three-step process is:
1. Determine the metric(s) with the smallest value.
2. Determine whether any remaining service(s) are close enough to
this best value to also be considered. The quantification of “close
enough” is the factor. A factor of 0 means consider only services
with the best value.
3. Randomly choose from all the services identified in the first two
steps.
A good example of the usefulness of this “close enough” threshold
factor is when two unequal servers are deployed behind different load
balancers. Server A may be capable of handling 3000 connections per
second. Server B may also be capable of handling that many
connections per second, but is also serving more sites than Server A.
The realistic connection limit of Server B may therefore only be
about 500 connections per second. If Server A has 900 connections
and Server B has 400 connections, then Server B is the site with the
least number of connections, although it is already 80% loaded while
Server A is only 30% loaded. The better choice would be to give the
traffic to server A. However, the SA9200 has no knowledge of the
actual load potential of the servers underneath the load balancers it
monitors. Therefore it allows the next best thing. For example, it