AFCs require a load balancer in front of the active nodes, but
both nodes can operate at the same time, providing scalability with high availability.
Figure 15-3 shows the differences between these two types of failover configurations.
Of course, many uses of Oracle Application Server involve multiple
services, such as Java, identity management, and database access. To
use clustering for high availability, you must avoid single points of failure
for all of these services. This can require careful planning and
multiple clustering and failover schemes.
For easier creation of clusters, AS comes with a feature called Distributed Configuration
Management (DCM), which simplifies creating clones of existing nodes and
redistributes J2EE components to the new node.
Figure 15-3. Cold Failover and Active Failover Clusters
Clients
Inactive
infastructure Active
infastructure
V. host Hardware
cluster
$ORACLE_HOME
-OID
-SSO
-DAS
-Infrastructure
DB instance
Clients
Active
infastructure
node 1
Active
infastructure
node 2
Hardware
cluster
Infrastructure
DB files
OID 2
SSO 2
DAS 2
DB instance 2
Load balancer
OID 1
SSO 1
DAS 1
DB instance 1
Config files
($0_H1)
Config files
($0_H2)
Middle
Tier
Shared
storage
Shared
storage
Local
storage
Local
storage
Middle
Tier
Middle
Tier
Middle
Tier
Oracle SOA Suite | 345
Oracle Application Server 10g and newer releases also leverage a feature in the database
called failover notification.
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