R12 file system has come up with new model – Code, Data, Configurations are segregated nicely to have easy maintenance, to avert NFS mount issues on shared appl tier configuration systems. Auto-config will not write anything in APPL_TOP, COMMON_TOP area in R12. All instance specific configurations, log files are written in INST_TOP area. Instance Home provides the ability to share Applications and technology stack code among multiple instances.

Tech  Stack  Components

DB_TIER

• 10.2.0.2 RDBMS ORACLE_HOME

APPL-TIER

• 10.1.2 C ORACLE_HOME / FORMS ORACLE_HOME (8.0.6 ORACLE HOME equivalence)‏
• 10.1.3 Java ORACLE_HOME/OC4J ORACLE_HOME (iAS ORACLE_HOME equivalence)‏
• INSTANCE_TOP : Each application tier has a unique Instance Home file system associated

R12  e-Biz & Application Server 10g

Application Server Releases and versions

There are two versions of Oracle Application server 10g (oAS10g) used,

• Oracle 10gAS R2: 10.1.2 – 10.1.2.2.0
• Oracle 10gAS R3: 10.1.3.0 – 10.1.3.3

In R12, 10.1.2 AS and 10.1.3 AS Homes are newly introduced in lieu of 8.0.6 and iAS(1.0.2.2) – 11i Architecture.

Why do we have 10.1.2. AS and 10.1.3 AS?

• 10.1.2 AS installation will be supporting forms based applications. It is Standalone 10.1.2 forms/reports server installation. Other components are not included.
• 10.1.3 AS tech-stack will be used by java based applications. 10.1.3 AS instance brings latest OC4J code which is successor of 10.1.2 AS. 10.1.3 AS release doesn’t contain forms/reports products.

Hence to take advantage of latest oc4j code 10.1.3 AS got introduced. But to support ebiz forms applications 10.1.2 AS introduced.

Directory  Structure

Below Image describes the complete directory structure for complete e-biz installation i.e. DB_TOP, APPL_TOP and new INST_TOP. If you dig into the INST_TOP you will find that it only contains all the configuration files, start-stop scripts, log files, certificate files, pid files etc.., so as to make DB_TOP and APPL_TOP untouched for any instance specific changes. So you can also make DB_TOP and APPL_TOP read only.

INSTANCE TOP
Instance home is the top-level directory for an Applications Instance which is known as Instance Home and is denoted the environment variable $INST_TOP. This contains all the config files, log files, SSL certificates etc.

Advantages of new INSTANCE HOME

• The additional Instance Home makes the middle tier more easy to manage and organized since the data is kept separate from the config files.
• The Instance Home also has the ability to share the Applications and Technology stack code across multiple instances.
• Another advantage of the Instance Home is that the Autoconfig writes only in INST_TOP so APPL_TOP and ORACLE_HOME can also be made read only file system if required.
• To create a new instance that shares an existing middle-tier, just create a new instance_top with proper config files and NFS Mount the middle tier

INSTANCE TOP – STRUCTURE

$INST_TOP      : $APPS_BASE/inst/apps/$CONTEXT_NAME/
/admin /scripts :  ADMIN_SCRIPTS_HOME: Find all AD scripts here
/appl              :  APPL_CONFIG_HOME. For standalone envs, this is set to $APPL_TOP
/fnd/12.0.0/secure : FND_SECURE: dbc files here
/admin             : All Env Config files here
/certs               : SSL Certificates go here
/logs                : LOG_HOME: Central log file location. All log files are placed here (except adconfig)
/ora                 : ORA_CONFIG_HOME
/10.1.2             : ‘C’ Oracle home config, Contains tnsnames and forms listener servlet config files
/10.1.3             : Apache & OC4J config home, Apache, OC4J and opmn
                         This is the ‘Java’ oracle home configuration for OPMN, Apache and OC4J
/pids                : Apache/Forms server PID files here
/portal              : Apache’s DocumentRoot folder

Shared Application Tier File System

We can configure multiple application node machines working with a single E-Business Suite database node. This creation of a “multi-node” E-Business Suite instance is frequently done to lower cost of ownership (many small machines are cheaper than one big one), increase fault tolerance (one machine fails, others do not), or scale the instance (support more users and a greater load).

When configuring Oracle E-Business Suite to use a shared application tier file system, the application tier node can be configured to perform any of the standard application tier services, such as Forms, Web, and Concurrent Processing (Batch).
Note the following definitions:

Node

A node/server/instance is a logical set of processes running on one hardware machine. In a single-node installation of Oracle E-Business Suite, all the Applications processes (including the database processes) run on one node, whereas in a multi-node installation, the processes are distributed across multiple nodes.
A multi-node installation of Release 12 supports both shared and non-shared application tier file systems. An application tier file system consists of:

• APPL_TOP file system (APPL_TOP and COMMON_TOP directories).
• Application tier technology stack file system (OracleAS 10.1.2 and 10.1.3 Oracle Homes).
• Instance Home (INST_TOP) file system. Each application tier has a unique Instance Home file system associated with it.

Service

A service is a functional set of Oracle E-Business Suite application processes running on one or more nodes. Where applicable, the term ’service’ is replacing the more traditional term of ’server’.

Application Tier Services

The following are the major application tier services:

• Root services
• Web Entry Point services
• Web Application services
• Batch Processing services
• Other services

So if you have two nodes,one will serve as Primary Node and other will serve as Secondry Node. You can configure both the Application tier node as follows:

Primary Application Tier Node

A primary application tier node is the first application tier node where the APPL_TOP, COMMON_TOP, OracleAS 10.1.2 Oracle Home and OracleAS 10.1.3 Oracle Home are installed and configured.

Secondary Application Tier Node

A secondary application tier node is an application tier node where APPL_TOP, COMMON_TOP, 10.1.2 Oracle Home and 10.1.3 Oracle Home are visible and configured. The APPL_TOP, COMMON_TOP, OracleAS 10.1.2 Oracle Home and OracleAS 10.1.3 Oracle Home file system is mounted to this node from the primary application tier node, or from an NFS server.
Instance Home

Note :  In a shared file system, each application tier will have a unique Instance Home, which should be located on the local file system.

Shared Application Tier File System Architecture
In a shared file system, all application tier files (with the specific exception of the Instance Home file system) are installed on a shared disk resource, which is mounted on each application tier node. Any application tier node can be configured to perform any of the standard application tier services, such as Forms, Web and Concurrent Processing (Batch) services. All changes made to the shared file system are immediately accessible to all application tier nodes.

Shared Application Tier File System Layout
When configuring Oracle E-Business Suite to use a shared application tier file system, an application tier node can be configured to perform any of the standard application tier services, such as Forms, Web, or Concurrent Processing (Batch) services. An application tier will have a unique Instance Home associated with it that cannot be shared with other application tiers. You can configure the services running on an application tier node to match the node’s intended role

Example Shared File System

The following is an example of mount points shared on each application tier node:

• COMMON_TOP: /ebiz/oracle/VIS/apps/apps_st/comn
• APPL_TOP: /ebiz/oracle/VIS/apps/apps_st/appl
• OracleAS 10.1.2 ORACLE_HOME: /ebiz/oracle/VIS/apps/tech_st/10.1.2
• OracleAS 10.1.3 ORACLE_HOME: /ebiz/oracle/VIS/apps/tech_st/10.1.3

In the figure shown below, entitled “Shared Application Tier File System”, Server-appl_node1 is the primary application tier node, and uses the file systems “/ebiz/oracle/VIS” and “/ebiz/oracle/inst”. The file system “/ebiz/oracle/inst” contains the Instance Home, and “/ ebiz/oracle/VIS ” contains the APPL_TOP, COMMON_TOP, OracleAS 10.1.2 and 10.1.3 Oracle Home.

Server-appl_node2 is the secondary application tier node, and the shared file system “/ebiz/oracle/VIS” is also mounted on this node. The file systems “/ebiz/oracle/inst/apps/VIS_appl_node1″ and “/ebiz/oracle/inst/apps/VIS_appl_node2″ are only visible on the respective nodes.