Hi Yongpyo,
Looking at your screenshots, I noticed one important difference between the two configurations.
Your working Database Connector is using:
jdbc:postgresql://tc2512:5432/demo
But in the External Database Connector, you're testing with:
jdbc:postgresql://localhost:5432/demo
If PostgreSQL is running on tc2512 and not on the same machine/container as the Mendix Runtime, localhost will point to the Mendix runtime machine itself, so the connection will fail.
I would first try changing the External Database Connector configuration to:
jdbc:postgresql://tc2512:5432/demo
with the same username and password that you use successfully with the Database Connector.
Also, the error dialog specifically says: Make sure to test your application locally with the latest External Database Connector module included.
So I would also make sure you have the latest version of External Database Connector installed, then restart the local Mendix application before testing the connection again.
In your case, I would check these in this order:
localhost to tc2512.Since the old Database Connector is already connecting successfully, the PostgreSQL database itself looks fine. The main differences are the host value and the External Database Connector version/configuration.
Kindly mark this as the accepted answer if it helps..