Docker Volume Plugin: Is there a way to map (or bind) the remote drive mounted inside the container with a local folder of the host machine?

General
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1

TL;NR

I have successfully mounted a remote drive in a docker container via the rclone Docker Volume Plugin, and everything works fine within the container.

I am wondering if it is possible to map that mounted drive inside the container to a local folder on the host machine?

Setup

Install the rclone Docker Volume Plugin

docker plugin install rclone/docker-volume-rclone:amd64 --alias rclone --grant-all-permissions

Set the Volume Plugin

docker plugin rclone disable
docker plugin set rclone RCLONE_VERBOSE=2 args="--uid 1000 --gid 1000 --umask 022 --buffer-size 128M"
docker plugin rclone enable

Configure the container with compose.yaml

version: "3.8"

networks:
  default:
    name: base
    driver: bridge
    attachable: true

volumes:
  gd:
    name: gd
    driver: rclone
    driver_opts:
      remote: 'gd:'
      allow_other: 'true'
      vfs_cache_mode: full
      vfs_cache_max_size: 100G
      vfs_cache_max_age: 12h
      dir_cache_time: 168h
      poll_interval: 0

services:
  busybox:
    image: busybox:latest
    container_name: busybox
    tty: true
    environment:
      - PUID=1000
      - PGID=1000
      - TZ=EST
    volumes:
      - gd:/mnt/gd

Behavior Observed

Inside the container busybox

up the container:

❯ docker compose up -d

exec the shell of the container:

❯ docker exec -it c2c171d2366139c65fea6e4d82e11abe00d4a7265572ed955678f406b4c43a30 /bin/sh -c eval $(grep ^$(id -un): /etc/passwd | cut -d : -f 7-)

access the remote drive within the container:

/ # ls -aln /mnt/gd
total 4
drwxr-xr-x    1 1000     1000             0 Jul  3 03:40 .
drwxr-xr-x   10 1000     998           4096 Jul  6 17:00 ..
drwxr-xr-x    1 1000     1000             0 Aug 13  2021 folder1
drwxr-xr-x    1 1000     1000             0 Sep  6  2021 folder2
drwxr-xr-x    1 1000     1000             0 May 13 03:28 folder3
/ #

Everything looks fine in the container, the remote drive mounted by the rclone driver from the volume plugin works as expected.

Question

So, when I am inside the container busybox, I can access the remote drive gd fine at /mnt/gd (container fs). I am wondering if it is possible to map (or bind) a local folder outside the docker container, say ~/gd (host machine fs) to the volume gd mounted within the busybox docker container? So that I don’t need to mount the remote drive with another dedicated rclone daemon.

Approach Attempted (but not working)

Initially, I thought it would achieve what I want if I bind a host machine folder to the parent folder of the directory that the remote drive is mounted on, because this way the mounted drive will be reflected under the host machine folder outside the container. Like this:

Create the host machine folder ~/mount

❯ mkdir -p ~/mount
❯ ls -aln ~/mount
total 8
drwxr-xr-x  2 1000 998 4096 Jul  6 19:54 ./
drwx------ 13 1000 998 4096 Jul  6 19:54 ../

Bind the host machine folders in compose.yaml

version: "3.8"

networks:
  default:
    name: base
    driver: bridge
    attachable: true

volumes:
+  mount:
+    name: local.mount
+    driver: local
+    driver_opts:
+      device: ~/mount
+      o: bind
+      type: local
  gd:
    name: gd
    driver: rclone
    driver_opts:
      remote: 'gd:'
      allow_other: 'true'
      vfs_cache_mode: full
      vfs_cache_max_size: 100G
      vfs_cache_max_age: 12h
      dir_cache_time: 168h
      poll_interval: 0

services:
  busybox:
    image: busybox:latest
    container_name: busybox
    tty: true
    environment:
      - PUID=1000
      - PGID=1000
      - TZ=EST
    volumes:
+      - ~/mount:/mnt
      - gd:/mnt/gd

restart the container to apply the newly updated compose.yaml

❯ docker compose down && docker compose pull && docker compose up -d

check the remote drives outside the container

❯ ls -aln ~/mount
total 12
drwxr-xr-x  3 1000 998 4096 Jul  6 20:02 ./
drwx------ 13 1000 998 4096 Jul  6 19:58 ../
drwxr-xr-x  2 1000 998 4096 Jul  6 20:02 gd/

❯ ls -aln ~/mount/gd
total 8
drwxr-xr-x 2 1000 998 4096 Jul  6 20:02 ./
drwxr-xr-x 3 1000 998 4096 Jul  6 20:02 ../

We can see the remote drive mounted inside the container is correctly reflected in the host machine folder, however, its content is empty.

Summary

So basically what I want to achieve is

remote drive <=> docker volume plugin <=> docker container <=> host machine filesystem

Please let me know if there is a viable way to achieve this.

Any help is much appreciated. Thank you!

2

Bind mount always replaces the content inside the container with the content on the host. You could try the bind propagations, but I don’t know if that works with another volume:

https://docs.docker.com/storage/bind-mounts/#configure-bind-propagation

You could also try to use rclone on the host and mounte the content from there.

3

In theory bind propagation should work with volumes backed by a bind as well, though I have no idea where and how to configure the propagation when creating the volume.

It will work with binds (as in not wrapped with a volume) and shared propagation, if you set the mount point to be shared:

mount --make-shared {mount point}

Use the host path you bind into the container as argument to --make-shared.