Yes, I tried deleting the fingerprint and using Test… as I said, it just immediately says Failed to Connect. It never shows me any option for using a new fingerprint (but it did the very first time I ran duplicati).
The “config directory” I mean is the persistent host folder defined as a volume when running this app as a container. So in my case -v /opt/duplicati:/data.
In any case, I did figure out a solution finally. I created a new temporary/dummy entry into my docker-compose.yml file to make a second instance of duplicati (called it duplicati2) with a different /data location (eg /opt/duplicati2) running on a different port and then started to make a test backup. Since this was the “first” time it was run, it did indeed offer me the are-you-ok-with-this-fingerprint thing, and I copied that and pasted in the previous instance’s backup config settings and all is ok in the world.
why in the world it refuses to show me that message, I do not know. It is frustrating but hopefully the next time it happens I’ll find this thread and see what to do to resolve it.
Nb: one issue may be that I originally didn’t know there was a duplicati/duplicati docker and I was using linuxserver/duplicati. I can’t for the life of me figure out why that would matter, but on a 2nd system I have that has only ever had duplicati/duplicati running… I do not have this same issue.
Side note: what’s really weird is that I installed a copy on my windows machine and tried connecting to the server and the fingerprint it gave was identical to the one I already had?!? Why would that be? I mean, that’s a fresh install connecting to the server for the first time and it saw the server as using the older style fingerprint.
By “older style”, I mean my old one was
ssh-rsa 3072 D5:A5:FE:B0:02:XX:XX:XX:EE:E8:F7:FA:10:15:7D:BD
while the “new one” that’s finally working is
ssh-ed25519 32 4C:76:87:07:0C:XX:XX:XX:9A:F0:2A:0D:4B:0C:16:7B