Cannot connect to Open SGID with [server closed the connection unexpectedly]

[steveoh]

The problem

Esri clients are unable to connect to the Open SGID. The common error message from a 10.7.1 client and Pro 2.5 is

Unable to get database list

A database connection exception has occurred. Unable to connect to database server to retrieve database list; please verify your server name, user name and password info and try again.
Underlying DBMS error[server closed the connection unexpectedly
This probably means the server terminated abnormally before or while processing the request. SQLSTATE=].

The reason

A network firewall is blocking network traffic

The workaround

Talk to your network IT professionals to make an exception in the firewall to allow traffic to the Open SGID.