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LXC To The Future

Create LXC virtual machines from any BTRFS subvolume. (origin is here)

Differences from Docker

This tool aims very much like what Docker does, with some key differences:

  • Requires a BTRFS filesystem to work with.
  • No black magic. You will/can assemble every moving part all by yourself. No overlays, no cryptic folder names, nothing.
  • Virtual machines can be converted back to host machines.
  • A virtual machine can be produced from a backup.

Install

git clone --recursive https://github.com/aktos-io/lxc-to-the-future
cd lxc-to-the-future
./snapshot-lxc

    Usage:

    	snapshot-lxc ...options


    Options

        --src /path/to/subvolume      : Subvolume source
        --name your-container-name    : Container name

        --delete your-container-name  : Delete the container
        --keep-ssh-keys               : Do not regenerate SSH keys
        --config-network              : Configure network after creation

Creating a fresh rootfs programmatically

Use the following to create custom rootfs programmatically:

./multistrap-helpers/create-rootfs.sh --use-subvolume multistrap-helpers/stable.config

Creating an LXC Container from an existing rootfs

If you want to create an LXC container from one of my snapshots:

$ ./snapshot-lxc --src /mnt/erik/snapshots/rootfs/rootfs.20170429T2001/ --name couchdb
creating the container directory: couchdb
creating a writable snapshot of given subvolume
Create a snapshot of '/mnt/erik/snapshots/rootfs/rootfs.20170429T2001/' in '/var/lib/lxc/couchdb/rootfs'
Creating new identity for /var/lib/lxc/couchdb/rootfs
Renew hostname from cca-erik to couchdb
Adding couchdb to TARGET/etc/hosts
Re-generating ssh private keys for users
...for ceremcem
Re-generating SSH Server Keys for /var/lib/lxc/couchdb/rootfs
...generating /var/lib/lxc/couchdb/rootfs/etc/ssh/ssh_host_rsa_key
...generating /var/lib/lxc/couchdb/rootfs/etc/ssh/ssh_host_dsa_key
...generating /var/lib/lxc/couchdb/rootfs/etc/ssh/ssh_host_ecdsa_key
...generating /var/lib/lxc/couchdb/rootfs/etc/ssh/ssh_host_ed25519_key
emptying the /etc/fstab file
remove the LXC specific entry from GUEST/etc/network/interfaces file
creating the config file
done in 3 seconds...

to run the vm:

	sudo lxc-start -n couchdb

to attach the root console:

	sudo lxc-attach -n couchdb

---------------------------------------------------
                  NOTE:

* Configure network in /var/lib/lxc/couchdb/config

---------------------------------------------------

To make network settings for your needs as stated above, see network-configuration

Start and attach the VM's console and test internet connection:

sudo lxc-start -n couchdb
sudo lxc-attach -n couchdb
root@couchdb:# ping google.com
PING google.com (216.58.206.206) 56(84) bytes of data.
64 bytes from sof02s28-in-f14.1e100.net (216.58.206.206): icmp_seq=1 ttl=51 time=64.5 ms
64 bytes from sof02s28-in-f14.1e100.net (216.58.206.206): icmp_seq=2 ttl=51 time=64.7 ms
^C
--- google.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 64.545/64.656/64.768/0.277 ms

Then make ssh:

ssh 10.0.8.8

Running GUI Applications

Make ssh connection with X Forwarding:

ssh -XC 10.0.8.8 freecad

or use x2go for slower connections.

Advantages

The machine on 10.0.8.8 is the exact copy of my snapshot located at /mnt/erik/snapshots/rootfs/rootfs.20170429T2001/

I can install/purge any software, run a database at that time, make any configuration changes and test them, run any of these machines forever nearly with no cost in terms of CPU, RAM (thanks to LXC), disk and time (thanks to BTRFS) resources.

Convert another VM to LXC container

In order to convert any VM (or any kind of remote machine) to LXC container,

  1. Use dcs-tools to make backup-root
  2. Use sync-root as LXC container source

Convert VM to Real Host

If I want to use that VM as my primary OS, I just need to snapshot the rootfs:

btrfs sub snap /var/lib/lxc/couchdb/rootfs /mnt/erik/rootfs_test
cd /mnt/erik/rootfs_test/etc
mv fstab.real fstab
mv hostname.real hostname
mv network/interfaces.real /network/interfaces
reboot

Press e at boot time and edit the GRUB entry (or add an entry your /boot/grub/grub.cfg) to boot from rootfs_test subvolume:

...
linux	/vmlinuz-4.9.0-2-amd64 root=/dev/mapper/erik-root ro  rootflags=subvol=rootfs_test
...

When your new system booted, check out if everything is OK.

If something went wrong in this step, simply reboot, all changes will be discarded.

If everything is OK, you can make it permanent:

cd /mnt/erik  # the device root
mv rootfs rootfs.bak
btrfs sub snap rootfs_test rootfs
reboot

If everything still goes well, clean the subvolumes:

btrfs sub delete /mnt/erik/rootfs_test
btrfs sub delete /mnt/erik/rootfs.bak

Convert VM to New Physical Machine

When your resources are not enough, you may want to convert your virtual machine into a new physical machine. To do so:

  1. Create an appropriate disk layout (/boot, /root over LVM over LUKS, for example) on a new disk
  2. Setup the bootloader (see create-bootable-backup.md)
  3. Change network settings
  4. Attach your new disk to your new hardware
  5. Power on.