I was breaking my head for a long time over this. I previously had a working function (not in app platform) that was connecting to an app platform development postgres database, all correct with the self-signed certificate and all. At some point it stopped working, I think when I promoted the dev db to a full managed database.
How I (somewhat) got it working again was by not using the (public) hostname of the database, but it’s IP address… I figured this out because I didn’t get errors from the TLS handshake, even when providing wrong ca certificate, so I figured it must be a lower level connectivity issue. So I did a DNS lookup inside the function, and noticed an IP address in range 10.x for the hostname, so private range. When I substitute the public IP address I get from a host lookup externally I get something in the 164.x range, so public range, and when I put this in the connection string it all starts working again.
The database has no trusted sources specified, i.e. it is accessible on the public IP. I did specify trusted sources at some point, maybe that caused a change in internal DNS servers?
So why is this, and how can I resolve it?
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