https://github.com/rclone/rclone
Specifically, check out this new beta feature called bisync which has use cases that sound a lot like yours:
https://rclone.org/bisync/#sharing-an-encrypted-folder-tree-...
a local filesystem remote
a cloud provider remote
rclone serve s3 to serve a local s3 compatible API for the local remote
something orchestating an rclone copy, rclone sync or rclone bisync command to sync the local and cloud remotes. Could be triggered on a timer, or using another tool to watch the local directory for changes and trigger a sync.
I think you can run rclone as a service, they recommend you use bisync on crontab, for example.
What's bisync? I don't really know, as it's new to me, but it's an experimental beta feature from rclone and sounds neat.
https://rclone.org/bisync/#sharing-an-encrypted-folder-tree-...
> Sharing an encrypted folder tree between hosts
> bisync can keep a local folder in sync with a cloud service, but what if you have some highly sensitive files to be synched?
> Usage of a cloud service is for exchanging both routine and sensitive personal files between one's home network, one's personal notebook when on the road, and with one's work computer. The routine data is not sensitive. For the sensitive data, configure an rclone crypt remote to point to a subdirectory within the local disk tree that is bisync'd to Dropbox, and then set up an bisync for this local crypt directory to a directory outside of the main sync tree.
