188 IBM Enterprise Workload Manager
7.1 EWLM and workload balancing overview
The EWLM domain manager has a global view of all the servers and middleware
technologies which make up the management domain that supports the business
applications, as described in 1.2.1, “Domain manager” on page 6. The domain manager
obtains performance information on each server and application instance, and knows how
much time a request is spending at each instance. The domain manager can use this
knowledge to influence network routing decisions made by a load balancer in order to
achieve the end-to-end business response time goal.
Without EWLM, when incoming requests arrive at a load balancer, the load balancer typically
has little information about the application’s health or the performance of the servers it is
routing to. It can use pure algorithmic techniques such as round robin, or general system
statistics represented by static, preconceived weights to route the incoming requests. Some
load balancers have algorithms that allow them to sense network state and forward requests
to the most capable instance, like the instance with the least number of sessions or
connections.
EWLM does not route the work itself, but provides recommendations to the routing entity
using the IBM Server/Application State Protocol (SASP). Through SASP messages a load
balancer can tell the domain manager which systems and applications it wishes to load
balance and the domain manager can make recommendations to load balancers regarding
how to distribute work. However, it is up to the load balancer to actually use EWLM’s
recommendations to route incoming requests to the members. Today, the load balancers that
exploit EWLM are from Cisco Systems Inc. and Nortel Networks.
7.2 Configuring an EWLM load balancing setup
Figure 7-1 shows the components of an EWLM management domain which consists of
managed servers, a domain manager, and a load balancer.
Figure 7-1 EWLM workload balancing components
Although it is assumed that customers who are using EWLM will most likely have
instrumented applications using ARM, the domain manager supports both application-level
Load
Balancer
Domain Manager
Managed ServerManaged Server
Managed ServerManaged Server
Managed ServerManaged Server
Incoming
Requests
Forwarded Requests
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SASP
Communication
EWLM Communication

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