To use database links from an Autonomous Database instance on a public endpoint, do the following:

1. Configure the Oracle Database Gateway to access a non-Oracle database. See Oracle Database Gateways in Oracle Database Heterogeneous Connectivity User's Guide for more details.

   Depending on the database you want to connect to, you may refer to the corresponding Installation and Configuration Guide and the Gateway User's Guide.

   For example, for Oracle Database Gateway for SQL Server see:

   • Installing and Configuring Oracle Database Gateway for SQL Server

   • Introduction to the Oracle Database Gateway for SQL Server in Oracle Database Gateway for SQL Server User's Guide.

   • Configure Oracle Net for the Gateway

2. Configure Oracle Net Listener to handle incoming requests on the Oracle Database Gateway.

3. Create a self signed wallet on the Oracle Database Gateway.

4. Configure the target gateway to use TCP/IP with SSL (TCPS) authentication. See Configuring Transport Layer Security Authentication for more information.

Use DBMS_CLOUD_ADMIN.CREATE_DATABASE_LINK to create database links from an Autonomous Database instance on a public endpoint to an Oracle Database Gateway to access Non-Oracle databases.

1. Copy the target gateway self signed wallet, for example, cwallet.sso, containing the certificates for the Oracle Database Gateway to Object Store.
   Note
   
   The wallet file, along with the Database user ID and password provide access to data available through the target gateway. Store wallet files in a secure location. Share wallet files only with authorized users.
2. Create credentials to access the Object Store where you store the cwallet.sso. See CREATE_CREDENTIAL procedure for information about the username and password parameters for different object storage services.
3. Create a directory on Autonomous Database for the wallet file cwallet.sso.
   For example:

   CREATE DIRECTORY dblink_wallet_dir AS 'directory_path_of_your_choice';

   See Create Directory in Autonomous Database for information on creating directories.

4. Use DBMS_CLOUD.GET_OBJECT to upload the target gateway self signed wallet to the directory you created in the previous step, DBLINK_WALLET_DIR.
   For example:

   BEGIN
       DBMS_CLOUD.GET_OBJECT(
           credential_name => 'DEF_CRED_NAME',
           object_uri => 'https://objectstorage.us-phoenix-1.oraclecloud.com/n/namespace-string/b/bucketname/o/cwallet.sso',
           directory_name => 'DBLINK_WALLET_DIR'
       );
    END;

   In this example, namespace-string is the Oracle Cloud Infrastructure object storage namespace and bucketname is the bucket name. See Understanding Object Storage Namespaces for more information.

   The credential_name you use in this step is the credentials for the Object Store. In the next step you create the credentials to access the target gateway.

   See GET_OBJECT Procedure and Function for more details.

5. On Autonomous Database, create credentials to access the target database. The username and password you specify with DBMS_CLOUD.CREATE_CREDENTIAL are the credentials for the target database used within the database link (where the target database is accessed through the Oracle Database Gateway).
   For example:

   BEGIN
       DBMS_CLOUD.CREATE_CREDENTIAL(
           credential_name => 'DB_LINK_CRED',
           username => 'NICK',
           password => 'password'
       );
   END;/

   Supplying the credential_name parameter is mandatory.

   The characters in the username parameter must be all uppercase letters.

   This operation stores the credentials in the database in an encrypted format. You can use any name for the credential name.

6. Create the database link to the target gateway using DBMS_CLOUD_ADMIN.CREATE_DATABASE_LINK.
   For example:

   BEGIN
       DBMS_CLOUD_ADMIN.CREATE_DATABASE_LINK(
           db_link_name =>       'SALESLINK',
           hostname =>           'example.com',
           port =>               '1522',  
           service_name =>       'example_service_name',
           ssl_server_cert_dn => 'ssl_server_cert_dn',
           credential_name =>    'DB_LINK_CRED',
           directory_name =>     'DBLINK_WALLET_DIR',
           gateway_link =>        TRUE
       );
   END;/

   Users other than ADMIN require privileges to run DBMS_CLOUD_ADMIN.CREATE_DATABASE_LINK.

   See CREATE_DATABASE_LINK Procedure for more information.

7. Use the database link you created to access data on the target gateway.
   For example:

   SELECT * FROM employees@SALESLINK;

BEGIN
    DBMS_CLOUD.UPDATE_CREDENTIAL(
        credential_name =>'DB_LINK_CRED',
        attribute =>'PASSWORD',
        value=>'password'
    );
END;
/