Backing up a LXD server¶
What to backup¶
When planning to backup a LXD server, consider all the different objects that are stored/managed by LXD:
Instances (database records and filesystems)
Images (database records, image files and filesystems)
Networks (database records and state files)
Profiles (database records)
Storage volumes (database records and filesystems)
Only backing up the database or only backing up the instances will not get you a fully functional backup.
In some disaster recovery scenarios, that may be reasonable but if your goal is to get back online quickly, consider all the different pieces of LXD you’re using.
Full backup¶
A full backup would include the entirety of /var/lib/lxd
or
/var/snap/lxd/common/lxd
for snap users.
You will also need to appropriately backup any external storage that you made LXD use, this can be LVM volume groups, ZFS zpools or any other resource which isn’t directly self-contained to LXD.
Restoring involves stopping LXD on the target server, wiping the lxd directory, restoring the backup and any external dependency it requires.
If not using the snap package and your source system has a /etc/subuid
and /etc/subgid file, restoring those or at least the entries inside
them for both the lxd
and root
user is also a good idea (avoids
needless shifting of container filesystems).
Then start LXD again and check that everything works fine.
Secondary backup LXD server¶
LXD supports copying and moving instances and storage volumes between two hosts.
So with a spare server, you can copy your instances and storage volumes to that secondary server every so often, allowing it to act as either an offline spare or just as a storage server that you can copy your instances back from if needed.
Instance backups¶
The lxc export
command can be used to export instances to a backup
tarball. Those tarballs will include all snapshots by default and an
“optimized” tarball can be obtained if you know that you’ll be restoring
on a LXD server using the same storage pool backend.
You can use any compressor installed on the server using the
--compression
flag. There is no validation on the LXD side, any
command that is available to LXD and supports -c
for stdout should
work.
Those tarballs can be saved any way you want on any filesystem you want
and can be imported back into LXD using the lxc import
command.
Disaster recovery¶
LXD provides the lxd recover
command (note the the lxd
command
rather than the normal lxc
command). This is an interactive CLI tool
that will attempt to scan all storage pools that exist in the database
looking for missing volumes that can be recovered. It also provides the
ability for the user to specify the details of any unknown storage pools
(those that exist on disk but do not exist in the database) and it will
attempt to scan those too.
Because LXD maintains a backup.yaml
file in each instance’s storage
volume which contains all necessary information to recover a given
instance (including instance configuration, attached devices, storage
volume and pool configuration) it can be used to rebuild the instance,
storage volume and storage pool database records.
The lxd recover
tool will attempt to mount the storage pool (if not
already mounted) and scan it for unknown volumes that look like they are
associated with LXD. For each instance volume LXD will attempt to mount
it and access the backup.yaml
file. From there it will perform some
consistency checks to compare what is in the backup.yaml
file with
what is actually on disk (such as matching snapshots) and if all checks
out then the database records are recreated.
If the storage pool database record also needs to be created then it
will prefer to use an instance backup.yaml
file as the basis of its
config, rather than what the user provided during the discovery phase,
however if not available then it will fallback to restoring the pool’s
database record with what was provided by the user.