Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 30)

14 Brocade Virtual ADX Server Load Balancing Guide
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Overview
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If the SNMP-weight indicates that your fastest server gets 50 percent of the connections, the server
will get 50 percent of the connections at a given time. However, because the server is faster than
others, it can complete more than 50 percent of the total connections overall by servicing the
connections at a higher rate. As a result, the weight is not a fixed ratio but instead adjusts to server
capacity over time.
Dynamic-weighted Reverse
The SNMP response from each server is regarded as a performance weight. Reverse-Weighted load
balancing is similar to Direct-Weighted, except that the SNMP-weight will be calculated by the
difference of the maximum based value and the dynamic SNMP response value (max. based value
– SNMP response). The server load balance will balance the same way as the direct-weighted
predictor with the dynamically calculated SNMP-weight value.
For an example of CPU usage, if you configure the maximum based value to 100% and the SNMP
response is 90% of CPU usage, the SNMP weight becomes 10% (100 - 90 = 10). The server load
balance does direct-weight load balancing with the 10% unused CPU time. In other words, servers
with a higher SNMP response (a higher CPU usage and lower SNMP-weight) receive a lower
percentage of connections at a time.
Server response time
Distributes traffic among real servers based on a dynamic weight value that is derived from the
response time of health check packets. If Layer 7 health check is enabled, application response
time is used. If Layer 4 health check in enabled, response time based on TCP SYN and TCP SYN
ACK packets is used. The response time weight is derived from the actual time response
measurement where the shorter the response time, the larger the response time weight value
computed. The response time wait is calculated according to the following rules:
• If the response time is 0, the weight is 1000
• If the response time is greater than 100 ms, the weight is 1
• If the response time is between 0.1 and 100 ms, the weight is 100 divided by the response
time (in 0.1 ms intervals)
The response time predictor is only applicable to TCP traffic.
The server response time predictors can be applied globally to apply for the entire Brocade Virtual
ADX or locally per virtual server as described in
“Changing the Load-Balancing Predictor Method”
on page 21.
Sticky connections
When a service request by a client mandates a series of sequential TCP or UDP port connections to
be served by the same real server, you can enable a sticky connection on that TCP or UDP virtual
server port. For example, if a user is accessing dynamically generated pages, the client must
consistently attach to the same server; otherwise, the state information is lost. By default, the
sticky parameter is disabled for virtual service ports.