7.4. Generating your bootc images from scratch

Prerequisites

• The container-tools metapackage is installed.

Procedure

• Create a Containerfile. The following is an example:

  # The following example reuses the default base image as a "builder" image. Optionally,  you can use the commented instructions to configure or override the RPM repositories in /etc/yum.repos.d to, for example, refer to pinned versions
  FROM registry.redhat.io/rhel10/rhel-bootc:latest
  # RUN rm -rf /etc/yum.repos.d/*
  # COPY mycustom.repo /etc/yum.repos.d
  RUN dnf repolist && /usr/libexec/bootc-base-imagectl build-rootfs --manifest=minimal /target-rootfs
  # Create a new, empty image from scratch.
  FROM scratch
  # Copy the root file system built in the previous step into this image.
  COPY --from=builder /target-rootfs/ /
  # You can make arbitrary changes such as copying the systemd units and other tweaks from the baseconfig container image. This example uses the heredocs syntax, to improve and make it easy to add complex instructions, and install critical components
  RUN <<EORUN
  set -xeuo pipefail
  # Install networking support and SSH which are not in minimal
  dnf -y install NetworkManager openssh-server
  dnf clean all
  rm /var/{log,cache,lib}/* -rf
  bootc container lint
  EORUN
  # This label is required
  LABEL containers.bootc 1
  LABEL ostree.bootable 1
  # These labels are optional but useful if you want to keep the default of running under systemd when run as a container image.
  STOPSIGNAL SIGRTMIN+3
  CMD ["/sbin/init"]

Next steps

• After creating your Containerfile, you get an image with a single tar file large layer. Every change, such as pushing to the registry, pulling for clients, results in copying the single large tar file, and increases the container image size. You can optimize the container image that you created for a smaller version.