bootc, a kind of bootable container

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bootc

bootc: Generating an ecosystem around bootable OCI containers https://cfp.all-systems-go.io/all-systems-go-2024/talk/LA9LXV/

live demo

• bootc status
• bootc switch
  • centos stream to fedora
• systemcl status bootc-fetch-apply-updates

What is bootable container?

• yes, container image as storage
• no, not a container or container engine; more like a deployer

What is Container?

An isolation Linux application.

• Open Container Initiative (oci)
  • docker
  • podman
• systemd-nspawn
• lxc

Extensions

• kubernetes - CRI (Container runtime interface)
  • containerd
  • cri-o

OCI Image

registry - https://github.com/opencontainers/distribution-spec

- hub.docker.io
- quay.io
- ghcr.io

image manifest / tar

• image
• list manifest
• type

backend storage

layers, images, and containers

• docker
  • overlay2 / fuse-overlayfs / btrfs and zfs / vfs
• podman / containers/storage

How it did?

Notes from 南部大聚

Note from Johnny Sung

https://www.facebook.com/share/p/129wP88YHmb/

ostree https://github.com/ostreedev/ostree Composefs https://github.com/containers/composefs 怎麼用

mount -t composefs /path/to/image.cfs -o basedir=/path/to/datafiles /mnt

EROFS: Enhanced Read-Only File System https://erofs.docs.kernel.org/en/latest/ bootc: Transactional, in-place operating system updates using OCI/Docker container images. https://github.com/containers/bootc Squashfs: compressed read-only filesystem for Linux https://zh.m.wikipedia.org/zh-tw/SquashFS https://docs.kernel.org/filesystems/squashfs.html bootc image builder https://docs.redhat.com/…/chap-anaconda-boot-options

Immutable solutions

Upgrade system always is a pain point for me, especially with package manager systems. They could work just sometime accident might happen, then need a lot of human operation to fix it.

There are lots of immutable solutions for os upgrade.

solution concepts:

• A/B switch
  • systemd usr-merge
• file system snapshot
• oci image

solutions:

• ubuntu snap
• nixos
• talos
• bootc/ostree
• elemental-toolkit

OCI ecosystem

• container engine - podman
  • build / pull images

bootc - bootable container

• ostree
• composefs

bootc as a bootable container runtime but it not really a runtime, more like a deployer.

https://github.com/containers/bootc

I really like bootc concept and thought it would the next docker.

podman with composefs as storage backend

Composefs state of the union

https://github.com/containers/storage/pull/1646

https://github.com/containers/storage/blob/main/docs/containers-storage-composefs.md

containers-storage.conf /etc/containers/storage.conf

pull_options = {enable_partial_images = "true", use_hard_links = "true", ostree_repos="",  convert_images = "true"}

[storage.options.overlay]
use_composefs = "true"

[storage.options.pull_options]
convert_images = "true"

• mount-cfs-oci.sh

#!/bin/bash

TAG=${TAG:=docker.io/library/alpine:latest}
MNT=${MNT:=/mnt}

BASEDIR=/var/lib/containers/storage/overlay
INDEX_FN=$BASEDIR/../overlay-images/images.json


LAYER=$(cat ${INDEX_FN} | jq -r '.[] | select( .names |  any( "$TAG" ) )  | .layer')

mount -t composefs ${BASEDIR}/${LAYER}/composefs-data/composefs.blob -o basedir=${BASEDIR} $MNT

$ podman pull quay.io/centos-bootc/centos-bootc:stream9
$ podman image save quay.io/centos-bootc/centos-bootc:stream9 -o stream9.tar #(oci)

# podman image mount  quay.io/centos-bootc/centos-bootc:stream9
/var/lib/containers/storage/overlay/98cf94224120f2355d5efc4df25632f6789c3b251f52cc0893562f959d72a7f6/merged
# mkcomposefs /var/lib/containers/storage/overlay/98cf94224120f2355d5efc4df25632f6789c3b251f52cc0893562f959d72a7f6/merged --digest-store=/sysroot/composefs/repo /sysroot/composefs/images/bootc-cs9.cfs

# mount -o rw,remount /sysroot/
# initrd
#mount --bind /sysroot /sysroot.tmp

Containerfile `ln -s sysroot/composefs composefs`


mkdir /sysroot.tmp
mount /dev/vda3 /sysroot.tmp

mount -t composefs /sysroot.tmp/composefs/images/bootc-cs9.cfs -o basedir=/sysroot/composefs/repo /sysroot

mount --bind /sysroot.tmp/ostree/deploy/default/deploy/37595a2f96fc23131eef6af87920858e6eecc4de5540ef3278aa7e184c7d4d5c.0/etc /sysroot/etc
mount --bind /sysroot.tmp/ostree/deploy/default/var /sysroot/var

modprobe zram
modprobe xfs