Alteon Application Switch Operating System Application Guide
Server Load Balancing
Document ID: RDWR-ALOS-V2900_AG1302
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Response Time
The response metric uses the real server response time to assign sessions to servers. The response
time between the servers and Alteon is used as the weighting factor. Alteon monitors and records
the amount of time it takes for each real server to reply to a health check to adjust the real server
weights. The weights are adjusted so they are inversely proportional to a moving average of
response time. In such a scenario, a server with half the response time as another server receives a
weight twice as large.
Note:
The effects of the response weighting apply directly to the real servers and are not
necessarily confined to the real server group. When response time-metered real servers are also
used in other real server groups that use the leastconns, roundrobin, or (weighted) hash metrics,
the response weights are applied on top of the metric method calculations for the affected real
servers. Since the response weight changes dynamically, this can produce fluctuations in traffic
distribution for the real server groups that use these metrics.
Bandwidth
The bandwidth metric uses real server octet counts to assign sessions to a server. Alteon monitors
the number of octets sent between the server and Alteon. The real server weights are then adjusted
so they are inversely proportional to the number of octets that the real server processes during the
last interval.
Servers that process more octets are considered to have less available bandwidth than servers that
have processed fewer octets. For example, the server that processes half the amount of octets over
the last interval receives twice the weight of the other servers. The higher the bandwidth used, the
smaller the weight assigned to the server. Based on this weighting, the subsequent requests go to
the server with the highest amount of free bandwidth. These weights are assigned.
The bandwidth metric requires identical servers with identical connections.
Note:
The effects of the bandwidth weighting apply directly to the real servers and are not
necessarily confined to the real server group. When bandwidth-metered real servers are also used in
other real server groups that use the leastconns, roundrobin, or (weighted) hash metrics, the
bandwidth weights are applied on top of the metric method calculations for the affected real servers.
Since the bandwidth weight changes dynamically, this can produce fluctuations in traffic distribution
for the real server groups that use the above metrics.
Group Availability Threshold
This feature lets you set the thresholds that define changes to a group’s availability:
•
Down threshold (minimum threshold)—When the number of active real servers reaches this
threshold, the group status changes to down.
•
Restore threshold (maximum threshold)—When the number of active real servers reaches
this threshold, the group status changes to up.
Example
A group has 10 real servers, the down threshold is 3, and the restore threshold is 5.
•
As long as there are more than three real servers active, the group is up.
•
If any of the group’s real servers fail and the number of active servers reaches three, the group’s
status changes to down.
