Chapter 7. Using load balancing 191
The load balancer needs to be able to communicate with the domain manager using the
SASP protocol. The way in which this is configured is vendor-specific and sometimes
version-specific. In general, the load balancer has a way in which the connection criteria for
the domain manager can be given and identified as the way to get dynamic weights for a
particular group.
The current implementation from Cisco System Inc. does this by creating a special DFP
agent that supports the SASP protocol. This SASP agent is configured with the domain
manager’s IP address and port information and is identified by a special BIND ID. This BIND
ID is also assigned to the server farm to identify the agent to be used to get dynamic weights
for this group.
7.3 Interfaces
This section describes the types of interfaces between the different elements.
7.3.1 Load balancer to domain manager (SASP communication)
The load balancer connects to the domain manager to:
? Register groups and instances within a group
? Deregister groups and instances
? Quiesce instances
? Set the load balancer configuration parameters to:
– Allow instances to register/deregister themselves by setting a trust flag
– Define the way weights are sent (pushed or pulled from the domain manager)
? Get (or receive) the current weights from the domain manager
7.3.2 Load balanced instances to domain manager (SASP communication)
A load balanced instance connects to the domain manager to:
? Register itself (provided the trust flag has been set by the load balancer)
? Deregister itself (provided the trust flag has been set)
? Quiesce itself
7.3.3 Domain manager to load balanced instances (Platform APIs)
A domain manager can communicate to the load balanced instances to:
? Obtain all the IP addresses that are defined to the platform
? Obtain the process ID (PID) of the application the load balancer was registering
7.4 Load balancing algorithm
In system-level balancing, either the load balancer or a member application can register the
instance. When the managed server comes up, it connects to the EWLM domain manager.
Statistical data at the server level is obtained for each instance of the server group. This data
is analyzed, and weighted (prioritized) by the domain manager. The weights can then be
passed to the load balancer to help achieve a better distribution of the work. If
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