WebSphere Application Server V8.5 Concepts, Planning, and Design Guide

Chapter 8. Topologies 209

8.3.5 Horizontal scaling topology

In a horizontal scaling topology, you create one logical unit of servers across multiple systems

or LPARs where each member of the unit serves each request. Horizontal scaling at the

application server tier does not require an IP sprayer. If you also want to scale at the web

server tier, you can use an IP sprayer.

This section introduces two topologies. One is without an IP sprayer, and the other has the IP

sprayer component. For more information, see 8.3.6, “Horizontal scaling topology with an IP

sprayer” on page 211.

Horizontal scaling topology without an IP sprayer

In the topology illustrated in Figure 8-7, a single application spans multiple systems, but

presents itself as a single logical image. In this example, the WebSphere Application Server

cluster spans Systems B and C, each with one application server. The deployment manager

is installed on a separate server, System D.

Figure 8-7 Horizontal scaling with cluster

The web server plug-in distributes requests to the cluster members on each server that runs

load balancing. It offers an initial failover in a similar manner as it does in the vertical

clustering topology. If any component (hardware or software) on System B fails, the

application server on System C can continue to serve requests and vice versa.

System B System C

Cluster

System D

System A

Web

server

Deployment

manager

Directory

and

security

services

Existing

applications

and data

Outside World DMZ Internal Network

Protocol firewall

Domain firewall

I

N

T

E

R

N

E

T

User

HTTP/HTTPS

Application

server 1

Application

server 2

Important: The illustration in Figure 8-7 is intended to show a horizontal scaling topology

of application servers but still contains a SPOF (namely, the web server). To avoid this

SPOF, you must enhance the topology as illustrated in 8.3.6, “Horizontal scaling topology

with an IP sprayer” on page 211.

210 WebSphere Application Server V8.5 Concepts, Planning, and Design Guide

Advantages

Using horizontal scaling with clusters has the following advantages:

 Improved throughput

Because multiple systems service client requests simultaneously without competing for

resources, you can expect improved throughput from your installation.

 Improved response times

By hosting cluster members on multiple systems, each cluster member can use the

processing resources of the system, avoiding bottlenecks and resource contention.

Therefore, response times improve in most scenarios.

 Benefits from the workload management capabilities of WebSphere Application Server

Because horizontal scaling is implemented through clusters, it benefits from the workload

management capabilities of WebSphere Application Server.

 Provides enhanced failover support

Because the cluster members are spread over multiple systems, this topology provides

hardware failover capabilities. Client requests can be redirected to cluster members on

other systems if a system goes offline. The outage of a system or an operating system

failure does not stop a service from working.

Considerations

Keep in mind the following considerations when using horizontal scaling with clusters:

 Increased resource usage

Because multiple systems are required to implement this topology, hardware costs

increase. To implement horizontal scaling, you need WebSphere Application Server

Network Deployment. Therefore, you need additional application server processes, such as

the deployment manager and the node agent process, to manage this type of environment.

This method increases processing and the memory footprint of the installation.

 More complex administration

The maintenance and administration of the environment are more complex because the

number of systems increases.

Setting up the topology

To set up a topology environment similar to the one illustrated in Figure 8-7 on page 209,

complete the steps in this section. These steps include the minimum software configuration

that you need for this topology.

Setting up System A

To set up System A, complete the following steps:

1. Install IBM Installation Manager.

2. Using Installation Manager, install the following applications:

– Web server plug-ins for WebSphere Application Server

– WebSphere Customization Toolbox

– IBM HTTP Server

If you are not using IBM HTTP Server, install a supported web server.

3. Open the WebSphere Customization Toolbox, and start the Web Server Plug-ins

Configuration Tool.