What is the ifile directive sometimes used in tnsnames.ora?

My customer is using Oracle E-Business Suite, and during a so-called "autoconfig", some files in the Oracle RDBMS home on the database server is overwritten.

Oracle eBS actually warns the DBA against changing these files manually. Here is an example from the $TNS_ADMIN/tnsnames.ora:

###############################################################
#
# Do not edit settings in this file manually. They are managed
# automatically and will be overwritten when AutoConfig runs.
# For more information about AutoConfig, refer to the Oracle
# E-Business Suite Setup Guide.
###############################################################

Since we are using multitenant architecture, and also use Golden Gate to extract data, we need to tnsnames.ora entries for the Golden Gate setup:

One entry for the pluggable database

One entry for the container database

After the initial setup, before the Golden Gate installation was ready, the $TNS_ADMIN/tnsnames.ora contained only the first of these two entries:

ebsref=
        (DESCRIPTION=
            (ADDRESS=(PROTOCOL=tcp)(HOST=ebs-ref-db01.oric.no)(PORT=1537))
            (CONNECT_DATA=
                (SERVICE_NAME=ebs_ebsref)
                (INSTANCE_NAME=cdb)
            )
        )

This entry is fine for the first of our two required connections. But there was no one supporting a direct connection to the root container, in my case called "cdb".
The listener process already supports a service called "cdb":

Services Summary...
Service "cdb" has 1 instance(s).
  Instance "cdb", status READY, has 1 handler(s) for this service...
Service "ebsref" has 1 instance(s).
  Instance "ebsref", status UNKNOWN, has 1 handler(s) for this service...

But we cannot add the necessary Golden Gate configuration unless we add another entry in the tnsnames.ora file.

How to do this, when we are not supposed to edit the tnsnames.ora because it eventually will be overwritten by autoconfig?

The answer was actually already in the tnsnames.ora file.

Oracle has included an example of how to use an include file in the tnsnames.ora file, so we can add our entries according to our needs. At the bottom of the file, you can see this string:

IFILE=/u01/oracle/sw/19c/network/admin/ebsref_ebs-ref-db01/ebsref_ebs-ref-ref-db01_ifile.ora

The file does not exist, so you need to create it:

vi /u01/oracle/sw/19c/network/admin/ebsref_ebs-ref-db01/ebsref_ebs-ref-ref-db01_ifile.ora

Add the following:

cdb = (DESCRIPTION=
          (ADDRESS=(PROTOCOL=tcp)(HOST=ebs-ref-db01.skead.no)(PORT=1537))
                (CONNECT_DATA= (SERVICE_NAME=cdb)
                (INSTANCE_NAME=cdb))
      )

And you've solved your problem, the connect identifier "cdb" can now be used by Golden Gate connections to the container database. Burleson Consulting has an article about ifile that actually points out eBS as the very reason for the ifile directive:

According to some Oracle experts, the ifile facility was designed for the init.ora file and ifile is not supported for the listener.ora, sqlnet.ora and protocol.ora files, but Oracle eBusiness Suite (EBS) release 11 uses ifile in their parameter files, ostensibly for reasons of customizations. With a ifile, you can leave the original file intact and not wonder what was added later.