Hi!
I managed to get it worked with an existing Nextcloud installation 
If you are interested in getting tardigrade as an external storage, just follow these steps:
1. Follow the official documentation until the step “Run the S3 gateway”, included.
nb: there is an error in the command to run the gateway. It shouldn’t be “./uplink_linux_amd64 setup” but rather “./gateway_linux_amd64 setup”
2. Go to “Settings > Administration > External Storage” page
3. Add an S3 storage
Some insights about important parameters to be set:
- Authentication: Access key
- Bucket: an existing bucket name (previously created on your tardigrade account)
- Hostname: 127.0.0.1
- Port: 7777
- Enable Path style: Yes
- Access key: Your access key (prompted when you start the gateway_linux_amd64 script
- Secret key: Your secret key (prompted when you start the gateway_linux_amd64 script
That’s it!
I just did it so it may have some bugs I didn’t see yet…