Chapter 8. Topologies 211
4. Configure the web server plug-in, and create the web server definition. For more
information, see the Websphere Application Server V8.5 Information Center at:
http://www14.software.ibm.com/webapp/wsbroker/redirect?version=phil&product=was
-base-dist&topic=tins_webplugins
Setting up Systems B and C
To set up Systems B and C, complete the following steps:
1. Install IBM Installation Manager.
2. Using Installation Manager, install WebSphere Application Server Network Deployment
V8.5.
3. Create an application server profile, also known as a custom profile:
–Use the app_server_root/profileTemplates/managed profile template. Then federate
this profile to the deployment manager on System D during profile creation or after
profile creation by running the addNode command.
–Use the app_server_root/profileTemplates/default profile template. Then federate
the node to the deployment manager that runs on System D by using the addNode
command.
Setting up System D
To set up System D, complete the following steps:
1. Install IBM Installation Manager.
2. Using Installation Manager, install WebSphere Application Server Network Deployment
V8.5.
3. Create an application server profile:
–Use the app_server_root/profileTemplates/dmgr profile template.
–Use the app_server_root/profileTemplates/management template, and specify
-serverType for DEPLOYMENT_MANAGER.
4. Create a web server definition through the administrative console or the wsadmin scripting
interface.
5. Create a WebSphere Application Server cluster with one cluster member on System B
and one cluster member on System C.
8.3.6 Horizontal scaling topology with an IP sprayer
You can use load balancing products to distribute HTTP requests among web servers that are
running on multiple physical systems. The load balancer component of Network Dispatcher,
for example, is an IP sprayer that runs intelligent load balancing among web servers based on
server availability and workload.
The active load balancer hosts the highly available TCP/IP address, the cluster address of
your service, and spray requests to the web servers. At the same time, the load balancer
tracks web server health and routes requests around web servers that are not available. To
avoid having the load balancer be a SPOF, set up the load balancer in a hot-standby cluster.
The primary load balancer communicates its state and routing table to the secondary load
balancer. The secondary load balancer monitors the primary load balancer through heartbeat
and takes over when it detects a problem with the primary load balancer. Only one load
balancer is active at a time.
212 WebSphere Application Server V8.5 Concepts, Planning, and Design Guide
Both web servers are active at the same time. They run load balancing and failover between
the application servers in the cluster through the web server plug-in. The plug-in detects any
component on System C or System D that fails, and the other server can continue to receive
requests.
Figure 8-8 illustrates a horizontal scaling configuration that uses an IP sprayer to redistribute
requests between web servers on multiple systems.
Figure 8-8 Simple horizontal scaling topology with an IP sprayer
Advantages
Using an IP sprayer to distribute HTTP requests has the following advantages:
Improved throughput and performance
By maximizing parallel processor and memory usage, you can expect increased
throughput and performance. The distribution of incoming TCP/IP requests among a
group of web servers spreads the workload among the available application servers. This
sharing helps to improve performance.
Increased capacity
The usage of multiple web servers increases the number of connected users that can be
served at the same time.
Elimination of the web server as a SPOF
Used in combination with load balancers, this topology eliminates the web server as a
SPOF.
Considerations
Keep in mind cost considerations when using a load balancer. It also causes increased
complexity. This configuration requires the load balancer component to be installed and
maintained. Therefore, this component increases the complexity of the installation and
System C
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Web
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Web
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Application
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Existing
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HTTP/HTTPS

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