Error "Channel is in state TRANSIENT_FAILURE" connecting to PostgreSQL

Issue

When connecting to PostgreSQL via proxy server from Tableau Desktop, the following error may occur:

Bad connection: Tableau could not connect to the data source.
Error code: FAB9A2C5
Channel is in state TRANSIENT_FAILURE
Unable to connect to the PostgreSQL server 'xxxxx'. Check that the server is running and that you have access privileges to the requested database.

Environment

Tableau Desktop
PostgreSQL
JDBC driver for PostgreSQL
System Proxy is turned on in Internet Options of Windows

Resolution

Option 1

In the Windows search box, type Internet Options and hit Enter.
Open the Connections tab and click LAN settings.
In the Proxy Server section, click Advanced to add the following exception: 127.0.0.1,localhost,database address.
- NOTE: do not use wildcards (*) - specify the full IP address and/or FQDN.
Click OK to close the window.

Option 2

Delete the environment variables HTTP_PROXY and HTTPS_PROXY.

Option 3

Add an environmental variable NO_PROXY to bypass a proxy server.

On the Windows search box, type sysdm.cpl and hit Enter.
Open the Advanced tab and click Environmental Variables.
In the system variables section, click New to add the following environmental variable:
- Variable: NO_PROXY
- Value: 127.0.0.1;localhost;database address.
  - NOTE: do not use wildcards (*) - specify the full IP address and/or FQDN.
Click OK to close the window.

Set an exception so that the proxy server will not be used for communicating with localhost and the database.

Cause

Java Server requires access to localhost. Thus, if there is a proxy server configured on the machine where Tableau Desktop is running, the Java process will try to communicate with Tableau Desktop via the proxy server and it will fail if localhost cannot be accessed directly.