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An end-to-end WebSphere environment, as shown in Figure 15-1, involves many different components, such as the Web server, firewalls, appservers, directory servers, databases, and so forth.
Figure 15-1 End-to-end WebSphere environment
A component box in Figure 15-1 does not mean that this is also a separate hardware system. Many of these components can be collocated on one physical system (even though for security reasons you might want to use multiple LPARs or multiple systems).
Each of these components can become a single point of failure if it is not made highly available, with different effects on your entire system. For example, if your network sprayer, which is the entry point into your system, fails, no Internet clients can access your application any more. If your directory server (LDAP) fails, only those parts of the application that need authentication are affected. However, this could be the most important part of your application so it might still be very important to have a HA directory server. Refer to Chapter 1, Understanding high availability concepts for conceptual information about WebSphere system availability.
Each component in a WebSphere system offers different options on how it can be made highly available. In this chapter, we discuss HA options for the following:
| WebSphere Load Balancer |
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| Web server |
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| Database server |
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| LDAP Server |
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| Firewall |
This chapter does not discuss HA options for the WebSphere components themselves. For this information, see Chapter 2, WAS failover and recovery.
