48 Barracuda Load Balancer Administrator’s Guide
•
Number of Windows Terminal Server sessions, determined by an SNMP query. In order to use
this option, Real Servers must allow SNMP access to the public community by the Barracuda
Load Balancer.
•
A URL provided by each Real Server which specifies a load value. If this option is selected, the
Barracuda Load Balancer will poll the URL http://[Real Server IP Address]/barracuda_load/ and
expect the output to look like LOAD=23 (showing the load as an integer between 0 and 100).
Weights are assigned to each Real Server using the formula (100 - LOAD). For example, if the
Load URL value is 23, the Real Server will be assigned a weight of 77. In order for the URL
query to work, you must create a load determination script and make the results available by
running a Web server on the Real Server that responds to the poll at the Real Server’s IP address
and port 80.
If, for example, all Real Servers have the same number of Windows Terminal Server sessions, then
the Real Servers will be assigned the same weight. These weights will change as the number of
Windows Terminal Server sessions varies.
To configure Adaptive Scheduling for a Service:
1.
From the
Basic > Services
page, click
Edit
for the Service you wish to configure. The
Service
Detail
page will appear.
2.
In the Adaptive Scheduling pulldown, select the algorithm to use when making weight
adjustments.
3.
Click
Save Changes
.
Pre-Assigned Weight
If Adaptive Scheduling is operational, then the pre-assigned weights are not used. Otherwise, if some
of the Real Servers are faster or have more capacity than others, you can tell the Barracuda Load
Balancer to direct more traffic to them. Do this by specifying weight values for the Real Servers
providing a Service. Varying weight values indicate that some Real Servers should receive more of
the traffic load.
To pre-assign weight for a Real Server:
1.
From the
Basic > Services
page, click
Edit
for the Real Server you wish to configure. The
Real
Server Detail
page will appear.
2.
Enter the weight for the Real Server. Values are applied as a ratio against weights of all other
Real Servers for this Service. For example, a Real Server with a weight of 50 will get half the
amount of traffic as a Real Server with a weight of 100, but will get twice that of a Real Server
with a weight of 25.
3.
Click
Save Changes
.
Scheduling Policies
The Barracuda Load Balancer considers the weight values for the Real Servers and then applies a
scheduling algorithm, either Weighted Round-Robin or Weighted Least Connections, to determine
which Real Server gets the next connection.
In
Weighted Round-Robin
, Real Servers with higher weights get more connections than those with
lower weights and Real Servers with equal weights get equal connections. The scheduling sequence
is generated according to the Real Server weights. New connections are directed to the different Real
Servers based on the scheduling sequence in a round-robin manner. The shortcoming with this
method is that a majority of long-lived connections may go to the same Real Server.
Summary of Contents for Load Balancer
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