How to create a DB link between two Oracle RDS instances

Question

I'm trying to create a DB link between two Oracle RDS instances in two different VPCs.

I have created a peering VPC connection, added routes and edited security groups according to this guide. But I'm getting

"ORA-12154: TNS:could not resolve the connect identifier specified" error when querying using the DB link.

My DB link creation SQL is as below:

CREATE DATABASE LINK dblink
    CONNECT TO myuser IDENTIFIED BY password
    USING 'DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=172.10.2.239)(PORT=1521))(CONNECT_DATA=(SID=sid))';

Answer 1

You need to wrap the connection string in parentheses:

CREATE DATABASE LINK dblink
    CONNECT TO myuser IDENTIFIED BY password
    USING '(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=172.10.2.239)(PORT=1521))(CONNECT_DATA=(SID=sid)))';

Without the starting parenthesis, Oracle looks for a tnsnames.ora entry named "DESCRIPTION", which it doesn't find, which is why it throws the error "could not resolve the connect identifier specified".