WebSphere Application Server V7.0: Concepts ... - IBM Redbooks

4.2.3 High availability
In addition to the caching features provided by WebSphere Application Server
Network Deployment, you might consider using third party caching devices or
external caching infrastructures provided by IBM and third parties.
To use the caching mechanisms provided by WebSphere Application Server and
other components of your environment, the application must be designed for
caching as well. Therefore it is suggested to design caching in close cooperation
with the application architect.
After you are done with designing your cache locations complete your
implementation design to include the caching components.
Designing an infrastructure for high availability means to design an infrastructure
in a way that your environment can survive the failure of one or multiple
components. High availability implies redundancy by avoiding any single point of
failure on any layer (network, hardware, processes, and so forth). The number of
failing components your environment has to survive without losing service
depends on the requirements for the specific environment.
The following list helps to identify the high availability needs in your infrastructure:
► Talk to the sponsor of your project to identify the high availability needs for
each of the services used. Because high availability in most cases means
redundancy, this also means that high availability will increase the cost of the
implementation.
Not every service has the same high availability requirements. Therefore it
would be a waste of effort to plan for full high availability for these types of
services. Be careful when evaluating, as the high availability of the whole
systems depends on the least available component. Carefully gather where
and what type of high availability you really need to be able to meet the
service level agreement (SLA) and non-functional requirements.
► When you have gathered the high availability requirements, review every
component of the implementation design you developed in 4.1, “Infrastructure
planning” on page 94, and determine how significant this component is for the
availability of the service, and how a failure would impact the availability of
your service.
► Evaluate every component you identified in the previous step against the
following checklist:
– How critical is the component for the service?
The criticality of the component will have an impact on the investments you
are willing to take to make this component highly available.
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