Oracle APPS R12 Architecture – Technical Overview

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

  • 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

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 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


$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


This contribution’s credit goes to Muhammad Rafi Aamiri Madani

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