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LXD (w/ NFS Shares)

I have a fairly cheap Synology system managing my spinning rust storage. Block storage over iSCSI didn't perform very well, so I ended up on NFS. NFS works well enough, but unfortunately the support to mount a remote export just isn't there yet. You'll need to mount the NFS share on the host, push the mount into the container as a disk object, and adjust permissions as needed. Here's how I've accomplished this.

NFS Mount

Easy part! Share nfs as normal. This assumes you have the folder shared from the NFS server as share

mkdir -p /mnt/share
vim /etc/fstab
   ip.or.hostname:/volume1/share	/mnt/share	nfs4	defaults	0 0
mount /mnt/share

Prep Users & Permissions

I created system users and groups to handle the permissions of each share. I use the user to grant RW permissions, and the group to grant RO. I map the user and/or group to the user/group inside the container that needs access to the share.

addgroup --system --gid 300 mntShareRO
adduser --system --home /mnt/share --uid 300 --gid 300 mntShareRW
chown mntShareRW:mntShareRO /mnt/share
chmod 750 /mnt/share
chmod g+s /mnt/share

To allow a user to be remapped, you'll need to use /etc/subuid for users & /etc/subgid for groups

vim /etc/subuid
   # /mnt/share: container-1
   root:300:1

vim /etc/subgid
   # /mnt/share: container-1 container-2
   root:300:2

The format of the file is the root user, then the UID/GID to share, then how many shares are allowed. In the above example I've allowed 1 UID remap for RW access, and 2 GID remaps for RO access. To keep track of which container has access to what I like to add comments to ensure my numbers are accurate.

Configure the LXD Container

Use the following command to set the raw id mapping:

echo -en "uid 300 1000\ngid 300 1000" | lxc config set container-1 raw.idmap -
echo -en "gid 300 1000" | lxc config set container-2 raw.idmap -

The first id in the line is the Host UID, the second is the ID in the container. The two examples above map the mntShare Host user/group to the user/group at id 1000.

Finally add the disk to the container

lxc config device add container-1 share disk source=/mnt/share path=/mnt/share
  • container-1: container name
  • share: container new device name
  • disk: container new device type
  • source: host directory to share
  • path: container directory to place share
Note

Because the root user (on unprivileged containers) is actually mapped to a non-0 user on the container, the root user may not have access to do things in the container. If you need this to work, you'll need to configure the mappings appropriately.

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