Integrate rclone process

[sapk]

No description provided.

[ivandeex]

Three notes on rclone integration:

1. mount
   Currently when docker-volume-rclone starts an rclone mount it has to manually check.... that the mount has been successful. In the next release (v1.54 or v1.55) rclone mount --daemon remote: /mnt/path will natively fork and internally perform a check similar to isMounted().... and return exit code 1 if it fails (see daemonize after mount rclone/rclone#2968 (comment) and below). That change is currently being planned.

2. unmount
   The rclone background process will stop a mount on one of two conditions: signal 15 (requires pid, not used here) or external unmount, so that docker-volume-rclone's method.... continues to work. Just a note: it uses root-only umount while fusermount -u could be run by a non-root user that made a mount (with fallback to umount if package fuse is not installed). Also, both umount and fusermount -u will fail if a process keeps using the directory mounted. To be more robust, docker-volume-rclone could fallback to umount -l or fusermount -u -l after a timeout to avoid cascading deadlocks in docker applications.

3. zombies
   After unmount the rclone background process should be normally reaped by systemd but in a docker container this is not done by default. This issue was mentioned in Docker leaving zombie processes everytime i mount a vieux/sshfs volume to create a container. vieux/docker-volume-sshfs#78, discussed in docker stop command create <defunct> process trajano/docker-volume-plugins#29 and fixed in FIX #29: use Tini (offiically supported by Docker) to reap defunct glusterfs processes. trajano/docker-volume-plugins#30 (comment) (see the config.json patch....). docker-volume-rclone also needs to incorporate tini in its config to avoid zombies.

[ivandeex]

While embedding rclone as a library is out of scope of this issue, FYI there is a ticket rclone/rclone#633 to implement support for that in future.

[sapk]

I think it should be fairly possible to add a rclone serve docker command exposing a docker volume api if allowed by rclone maintainers.