From now onwards I'll discuss shared application tier & shared APPL_TOP interchangeably.
There are two scenarios in which you want to configure Shared Application tier like 1. You want to configure shared APPL_TOP at install time itself (During Initial Build/Fresh Install) 2. You already have multi node Installation and want to configure Shared APPL_TOP.
In case of fresh Install or configure shared application tier via Installer You first find a file system & share it across all servers ( Usually ask unix team to do so). Lets assume you want to configure shared appl_top on machine 1, 2 and 3 . Assume you have file system /u01/shared/appl_top, /u01/shared/comn_top, /u01/shared/ora_top local to any of these servers or on any file server like SAN or NAS , then mount it to all these three servers with same mount points assume in our case we mounted like /u01/shared/appl_top, /u01/shared/comn_top, /u01/shared/ora_top Then when rapid installer asks for mount points give shared mount points from all three or more machines. Rest Leave on Installer :)
In case to configure shared Application Tier on already installed multiple node 1. There is some minimum software version for some component you need , make sure you have appropriate version if not upgrade them . For version check metalink Note referenced at bottom of this in Related links section. 2. Then you need to enable Autoconfig if you already don't have Autoconfig enabled : To check more on Autoconfig visit http://teachmeoracle.com/autoconfig.html 3. If your exisiting xml file ( CONTEXT file) is of format SID.xml then you need it in format SID_HOSTNAME.xml ( This way each server will recognize its xml/context file ) . You can do same by perl script adclonectx.pl 4. Shared file system across all machine with same mount point as done above 5. You then finally run autoconfig to configure shared application tier