8 Container Snapshots

Throughout this chapter, you must run commands as your unprivileged user ("incusadmin" if you've been following them from the beginning of this book).

Container snapshots and a snapshot server (more on later) are the most critical aspects of running a production Incus server. Snapshots ensure quick recovery. It is a good idea to use them as a failsafe 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 of downtime.

The author used Incus containers for PowerDNS public-facing servers, and updating those applications became less problematic, 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:

incus snapshot create ubuntu-test ubuntu-test-1

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

incus info ubuntu-test

You have already looked at an info screen. 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:

incus shell ubuntu-test

Create an empty file with the touch command:

touch this_file.txt

Exit the container.

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

incus stop ubuntu-test

Restore it:

incus snapshot restore ubuntu-test ubuntu-test-1

Start the container again:

incus start ubuntu-test

If you return to the container again and look, the "this_file.txt" you created is gone.

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

incus snapshot delete ubuntu-test ubuntu-test-1

Warning

You should permanently delete snapshots while the container is running. Why? Well, the incus delete command also works to delete the entire container. If we accidentally hit enter after "ubuntu-test" in the command above, AND if the container was stopped, the container would be deleted. I just wanted to let you know that 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 the 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