Nortel Networks WEB OS 212777 - Manual (Page 133)

Web OS 10.0 Application Guide
Chapter 6: Server Load Balancing n 133
212777-A, February 2002
Response Time
The response metric uses real server response time to assign sessions to servers. The
response time between the servers and the switch is used as the weighting factor. The switch
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 will receive a weight twice as large.
N OTE – 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 or roundrobin metrics, the
response weights are applied on top of the leastconns or roundrobin calculations
for the affected real servers. Since the response weight changes dynamically, this can pro-
duce fluctuations in traffic distribution for the real server groups that use the leastconns or
roundrobin metrics.
Bandwidth
The bandwidth metric uses real server octet counts to assign sessions to a server. The switch
monitors the number of octets sent between the server and the switch. Then, the real server
weights are 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 band-
width used, the smaller the weight assigned to the server. Based on this weighting, the subse-
quent requests go to the server with the highest amount of free bandwidth. These weights are
automatically assigned.
The bandwidth metric requires identical servers with identical connections.
N OTE – 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 or roundrobin metrics, the
bandwidth weights are applied on top of the leastconns or round-robin calculations
for the affected real servers. Since the bandwidth weight changes dynamically, this can pro-
duce fluctuations in traffic distribution for the real server groups that use the leastconns or
roundrobin metrics.