Checkpoints wont work with minio

[remche]

Because of minio relying on POSIX namespace for file backend (minio/minio#1291), saving checkpoint fails with Object-prefix is already an object, please choose a different object-prefix name..

Choosing a different prefix for checkpoints will fix it.

[michalc]

Hi @remche,

Thanks for the report. This is a tricky one... while working with S3 is an aim of project, I'm torn about making changes for it to work with things that are not S3, or not fully S3-compatible, like minio.

I'll have more of a think, but in the meantime, right now you can probably monkey-patch the _checkpoint_path and _list_checkpoints functions in https://github.com/uktrade/jupyters3/blob/master/jupyters3/jupyters3.py to be more minio-compatible: _checkpoint_path converts the path of a notebook and a checkpoint ID to a path of a checkpoint file, and _list_checkpoints takes a path of a notebook and should return a list of {'id': ..., 'last_modified': ...} of checkpoints for that notebook.

Thanks,

Michal