Presentation

[gbraad]

Published at: https://gbraad-redhat.github.io/fedora-bootc-example/

[gbraad]

Bootable

Containers

---

From Containerfile

to Virtual Machine

Gerard Braad me@gbraad.nl

---

Containerfile

---

describes content

FROM

RUN, USER

COPY, ADD

---

what runs

CMD

ENTRYPOINT

---

or describes runtime use

EXPOSE

VOLUME

---

Example

CMD

---

FROM quay.io/fedora/fedora

RUN dnf install -y cowsay

CMD [ "cowsay", "Hello" ]

$ podman build -t cowsay -f Containerfile .
$ podman run --rm cowsay
$ podman run -it --rm cowsay bash

---

Example

ENTRYPOINT

---

FROM quay.io/fedora/fedora

RUN dnf install -y cowsay

ENTRYPOINT [ "cowsay" ]

$ podman run --rm cowsay Hello

---

Application Containers

---

Single process

Long running

supervisor process

---

System Containers

---

FROM ...

RUN dnf install -y systemd

ENTRYPOINT [ "/sbin/init" ]

$ podman run -d --name system system
$ podman exec system cowsay Hello

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System Containers

---

System and Service Manager

---

Still a container

No 'container'-provided kernel

---

What if ...

---

we include a kernel ?

and call it a Machine Container ?

---

Still a container

the container runtime

runs 'isolated' processes

using a namespace

---

Bootable Container

---

FROM quay.io/fedora/fedora-bootc

RUN useradd -m -d /var/home/admin -G wheel admin \
    && echo "admin:password" | chpasswd

...

---

Still a container

therefore easy to build and test

---

Important

The full container image name is:
ghcr.io/gbraad-redhat/fedora-bootc-example/fedora-bootc:latest
In most slides this will be shortened

---

$ podman build -t ghcr.io/.../fedora-bootc \
	-f Containerfile .
$ podman push ghcr.io/.../fedora-bootc

---

$ podman run -it ghcr.io/.../fedora-bootc bash
bash-5.2# cat /etc/os-release
NAME="Fedora Linux"
VERSION="41.20250119.0 (Forty One)"
...
OSTREE_VERSION='41.20250119.0'

---

Wait a minute

---

bootable machines

run /sbin/init

---

$ podman run -d --name test ghcr.io/.../fedora-bootc:latest
52cae56640ff...4840bff9
$ podman ps
CONTAINER ID  IMAGE           COMMAND     STATUS        NAMES
52cae56640ff  ghcr.io/...est  /sbin/init  Up 4 seconds  test

---

$ podman exec -it test bash
bash-5.2# uname -na
Linux 52cae56640ff 5.15.167.4-microsoft-standard-WSL2

---

We do not

boot containers

---

What if ...

---

We create a disk image

---

 $ sudo podman run \
    -v ./output:/output \
	quay.io/centos-bootc/bootc-image-builder
	  --target-arch amd64 \
	  --type qcow2 \
	  --rootfs xfs \
	  ... \
	  ghcr.io/gbraad-redhat/fedora-bootc-example/fedora-bootc

---

Start a

Virtual Machine

---

$ sudo virt-install \
    --name fedora-bootc \
    --cpu host \
    --vcpus 2 \
    --memory 2048 \
    --import --disk ./output/qcow2/disk.qcow2 \
    --os-variant fedora-eln

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Login

---

Use console or SSH

Note

Username: admin
Password: password
Groups: wheel

---

Recap

---

We used a

Containerfile

to describe the contents

---

We produced an

OCI

container-image

---

We converted this into a

qcow2

disk image

---

run a

container-image

---

as a

virtual machine

---

Why does

this matter ?

---

$ sudo bootc status
No staged image present
Current booted image: ghcr.io/.../fedora-bootc:latest
    Image version: 41.2025019.0 (...)
    Image digest: sha256:4074...
No rollback image present

---

Forgot to include

cowsay

---

$ sudo dnf install -y cowsay
Updating and loading repositories:

...
Transaction Summary:
 Installing:         1 package
...

Running transction
Transaction failed: Rpm transaction failed.
  - installing package cowsay needs 376KB more space on the / filesystem

---

Immutable

---

As a virtual machine

this runs as an immutable environment

---

ostree

Version control system on an entire filesystem

---

/etc, /var

to store configuration, state, ...

---

Instead we update the Containerfile

---

FROM quay.io/fedora/fedora-bootc

...

RUN dnf install -y cowsay

---

... build the new container image

---

$ podman build -t ghcr.io/.../fedora-bootc \
	-f Containerfile .

---

... we push this new container image

---

$ podman push ghcr.io/.../fedora-bootc

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... and update the virtual machine

---

$ sudo bootc update
layers already present: 82 ;layers needed: 1 (361 Kb)
Fetching layers [               ] 0/1
  Fetching [X               ] 4 Kb/261 Kb (80 KiB/s) layer 94232345fd423e24
...
* Deploying
  Deploying: done (5 seconds)
...

---

Reboot

---

$ sudo bootc status
Current staged image: ghcr.io/.../fedora-bootc:latest
    Image version: 41.2025019.0 (...)
    Image digest: sha256:990c...
...
$ sudo reboot

---

Success!

---

$ cowsay Hello

	 _______
	< Hello >
	 -------
	        \   ^__^
	         \  (oo)\_______
	            (__)\       )\/\
	                ||----w |
	                ||     ||

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Rollback

$ sudo bootc status
No staged image present
Current booted image: ghcr.io/.../fedora-bootc:latest
    Image version: 41.2025019.0 (...)
    Image digest: sha256:990c...
Current rollback image: ghcr.io/.../fedora-bootc:latest
    Image version: 41.2025019.0 (...)
    Image digest: sha256:4074...

---

Do I need a

non-bootc

container ?

---

$ sudo bootc status
System is not deployed via bootc.

---

Mutable

---

.devcontainer/devcontainer.json

{
    "name": "Fedora bootc example",
    "image": "ghcr.io/.../fedora-bootc:latest",

    "runArgs": [  ],

    "overrideCommand": false,
	"privileged": true,
    "remoteUser": "admin"
}

---

There is more

---

export different disk image types

target different architecture

config.toml for customization

Fedora, CentOS, RHEL

...

---

Resources

• https://github.com/gbraad-redhat/fedora-bootc-example

• https://github.com/gbraad-docs/presentation-podman-libvirt

• https://containers.github.io/bootc/

• https://osbuild.org/docs/bootc/

• https://gitlab.com/fedora/bootc/examples

• https://gitlab.com/fedora/bootc/base-images