Chapter 8: container snapshots

Throughout this chapter you will need to run commands as your unprivileged user ("lxdadmin" if you've been following along from the beginning of this book).

Container snapshots, along with a snapshot server (more on that later), are probably the most important aspect of running a production LXD server. Snapshots ensure quick recovery. It is a good idea to use them as a fail safe when updating the primary software that runs on a particular container. If something happens during the update that breaks that application, you just restore the snapshot and you are back up and running with only a few seconds worth of downtime.

The author used LXD containers for PowerDNS public facing servers, and the process of updating those applications became less worrisome, thanks to taking snapshots before every update.

You can even snapshot a container when it is running.

The snapshot process

Start by getting a snapshot of the ubuntu-test container by using this command:

lxc snapshot ubuntu-test ubuntu-test-1

Here, you are calling the snapshot "ubuntu-test-1", but you can call it anything. To ensure that you have the snapshot, do an lxc info of the container:

lxc info ubuntu-test

You have looked at an info screen already. If you scroll to the bottom, you now see:

Snapshots:
  ubuntu-test-1 (taken at 2021/04/29 15:57 UTC) (stateless)

Success! Our snapshot is in place.

Get into the ubuntu-test container:

lxc exec ubuntu-test bash

Create an empty file with the touch command:

touch this_file.txt

Exit the container.

Before restoring the container how it was prior to creating the file, the safest way to restore a container, particularly if there have been many changes, is to stop it first:

lxc stop ubuntu-test

Restore it:

lxc restore ubuntu-test ubuntu-test-1

Start the container again:

lxc start ubuntu-test

If you get back into the container again and look, our "this_file.txt" that you created is now gone.

When you do not need a snapshot anymore you can delete it:

lxc delete ubuntu-test/ubuntu-test-1

Warning

You should always delete snapshots with the container running. Why? Well the lxc delete command also works to delete the entire container. If we had accidentally hit enter after "ubuntu-test" in the command above, AND, if the container was stopped, the container would be deleted. No warning is given, it simply does what you ask.

If the container is running, however, you will get this message:

Error: The instance is currently running, stop it first or pass --force

So always delete snapshots with the container running.

In the chapters that follow you will:

• set up the process of creating snapshots automatically
• set up expiration of a snapshot so that it goes away after a certain length of time
• set up auto refreshing of snapshots to the snapshot server

Author: Steven Spencer

Contributors: Ezequiel Bruni, Ganna Zhyrnova