Shared Appl_Top and Shared application tier 11i

In the Shared APPL_TOP feature introduced by Oracle in E-Business 11i, Oracle allows multiple nodes to share a single APPL_TOP. In a shared APPL_TOP configuration, the APPL_TOP and COMN_TOP file systems can be installed on a single shared disk. The shared disk resource can then be shared via various network file protocols across multiple nodes to provide standard application tier services such as forms, web and concurrent processing. A shared APPL_TOP also significantly simplifies the patching or upgrade process since it has to be performed only once and changes made are immediately visible to all the nodes.

Here it is important to note that there is a difference between a Shared APPL_TOP and a Shared Application Tier File system. In a Shared APPL_TOP though the APPL_TOP(APPL_TOP and the COMMON_TOP ) is shared across different nodes, each nodes still have their individual ORACLE_HOME. In a Shared Application Tier FileSystem both the APPL_TOP and the ORACLE_HOME (ORA_TOP) reside on the shared disk.

Any changes on the shared TOPs like for example patch application is immediately visible to all the nodes of the
application tier.

Another important factor to be kept in mind is that SHARED APPL_TOPS will not work if different nodes are on different Operating systems. So its mandatory that the different nodes of the application tier run on a same operating system or in other words the different nodes must be binary compatible.

Also as of now the SHARED APPL_TOP feature is not available for the windows version of Oracle Applications.

There are various methods by with you can implement shared APPL_TOP like using Rapid Install or by merging existing APPL_TOPs. It is mandatory for you to have implemented autoconfig before you can proceed with the implementation of a Shared APPL_TOP.

While patching a shared APP_TOP you can just apply the path to any of the nodes and it will become visible to all the nodes, in case of applying a patch to 8.0.6 home or IAS_HOME you need to apply the patch only once but to a primary node.

Notes on maintaining a shared application tier file system:

Application tier environment file
The APPSORA.env environment file is not used in a shared application tier file system. The APPS.env environment file is used instead. Each application tier node has its own unique environment file, located in the shared APPL_TOP. When one of these environment files is used to set up the environment for a particular node, you must ensure that the file specific to that node is used.