62 Certification Study Guide: IBM Tivoli Access Manager for e-business 6.0
2.6.2 Sizing and availability
Availability is the major concern that a failing part of the infrastructure will cause
the overall solution to languish. This eventually leads to unsatisfied customers
and decreasing business success. Adding replicas of crucial servers increases
your site’s availability by avoiding single point of failure. All Access Manager
components can be replicated with the exception of the Policy Server, since
there can be only one Policy Server per secure domain. However, there can be a
second Policy Server in standby to provide manual fail-over capabilities as a first
aid response. If you want to assure 24x7 availability of your Access Manager
Policy Server you could implement a high-availability cluster solution such as
HACMP for AIX.
Before configuring a standby Policy Server, the files that it needs to operate must
be made available. To avoid synchronization problems, it is best to locate these
files on a shared file system.
In general, the most effective way to have a redundant Policy Server is to
configure an
original and standby Policy Server in an HACMP (or similar)
environment. This handles routing IP traffic to the active instance and can handle
(via scripting) the starting and stopping of the Policy Servers so that only one is
active at any time. IBM supports automatic failover only on the AIX platform.
Figure 2-12 shows a possible configuration that uses a network load-balancer to
direct SSL traffic to the active Policy Server. If it is not possible for the load
balancer to monitor the Policy Servers, then manual intervention (or custom
scripting) will have to be used to monitor the Policy Servers and switch to the
backup on failure.

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