Oracle B32100-01 User Manual

Overview of High Availability Configurations

Installing in High Availability Environments: Overview

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 Application independence

Some applications may not be suited to an active-active configuration. This may 
include applications which rely heavily on application state or on information 
stored locally. An active-passive configuration has only one instance serving 
requests at any particular time.

In general, the term OracleAS Cold Failover Cluster describes clustering at the Oracle 
Application Server instance level. However, if it is necessary to call out the specific 
type of instances being clustered, this document will use OracleAS Cold Failover 
Cluster (type) to characterize the cluster solution. For example:

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OracleAS Cold Failover Cluster (Identity Management)

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OracleAS Cold Failover Cluster (Infrastructure)

From the entry point of an Oracle Application Server system (content cache) to the 
back end layer (data sources), all the tiers that are crossed by a client request can be 
configured in a redundant manner either in an active-active configuration using 
OracleAS Clusterss or in an active-passive configuration using OracleAS Cold Failover 
Clusters. 

 for installation details.

Oracle Application Server provides an active-active model for all its components with 
OracleAS Clusters. In an OracleAS Clusters, two or more Oracle Application Server 
instances are configured to serve the same application workload. These instances 
typically run on different nodes. 

You need an external load balancer in front of the nodes. Clients direct requests to 
these nodes through the load balancer, which then sends the requests to one of the 
nodes for processing. The load balancer uses its own algorithm to decide which node 
to send a request to.

The most common properties of an OracleAS Clusters configuration include:

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Identical instance configuration

The instances are meant to serve the same workload or application. Their identical 
configuration guarantees that they deliver identical responses to the same request. 
Note that some configuration properties are allowed to be instance-specific, such 
as local host name information.

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Managed as a virtual single instance

Changes in configuration made to one instance usually need to be propagated to 
the other instances in an active-active topology.

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Independent operation

The loss of one Oracle Application Server instance in an active-active topology 
should not affect the ability of the other instances to continue to serve requests.

The advantages of an OracleAS Clusters configuration include:

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Increased availability

An active-active topology has built-in redundancy (multiple Oracle Application 
Server instances run the same components). Loss of one instance can be tolerated 
because other instances can continue to serve the same requests.