Image mode for Red Hat Enterprise Linux

Image mode is included in Red Hat Enterprise Linux 9.6 and later—including Red Hat Enterprise Linux 10. Users will start with a bootc base image, then customize it with their own applications, configurations, and packages using a Containerfile.

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Image mode is integrated within Red Hat Enterprise Linux. It can run everywhere Red Hat Enterprise Linux runs. Deploy it on:

• Bare metal servers: Depoly Red Hat Enterprise Linux and image mode directly onto physical hardware through standard installation mechanisms like anaconda and kickstart.
• Cloud instances: Red Hat Enterprise Linux can be run via image mode on major cloud providers like AWS, Microsoft Azure, Google Cloud Platform, and Alibaba Cloud, and others by adding appropriate guest tools.
• Virtual machines: You can deploy image mode within virtualized environments managed by hypervisors like Red Hat OpenShift Virtualization, Red Hat OpenStack Services on OpenShift, HyperV, VMware, KVM, and others by adding appropriate guest tools.
• Edge devices: Image mode is also suitable for deployment on edge computing devices, enabling consistent and manageable operating system deployments in distributed environments.

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Bootc is the enabling component for image mode. It uses a container image to install and manage systems. Bootc hosts the core of image mode operations, and it's also integrated into standard Red Hat tooling like anaconda, image builder, Red Hat Satellite, and more.

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The design goal for image mode is to move as much into the image definition via the Containerfile as possible. This maintains a single, known image that can be reused across multiple systems and footprints. Changes need to be made to the controlling Containerfile—and that new build should be promoted for packages, configuration files, etc. 

Not all configurations can be shared—like networking configurations or users. These can be managed locally per host through typical means like Anaconda, Ansible, or cloud-init.

Transient installation patterns are also available via dnf, which installs packages on a bootc host that only persists until the next reboot. This can help with troubleshooting and hotfixes. 

Changes to files in /etc are persistent across image updates on an image mode host. The management of files in /etc is shared between the image update and the local host via a process known as a 3-way merge. Any local changes to files from the container  image will no longer be updated from future images. This comparison is on a file by file basis, so it is entirely possible and safe to have some files in /etc managed via the image (like crypto policies) and others managed locally (like hostnames). If a file has been modified and you wish to “reset” it so it can be managed via the container image, simply copy the original file from the /usr/etc/ directory to /etc. This is a powerful feature not found on traditional Linux systems.

No. Package mode systems can not be converted to image mode, or vice versa. These new operating modes of RHEL are mutually exclusive. The new system-reinstall-bootc tool provides a simplified wrapper around an install option that replaces an existing package mode host with a new image mode host. This can be very useful for deployments where a traditional installation method, like creating a hypervisor specific disk image, isn’t desirable.

While both rhel-bootc and universal base images share roots in Red Hat Enterprise Linux, they serve distinct purposes and have different content and licensing. rhel-bootc is specifically designed as a foundational image for installing a lightweight Red Hat Enterprise Linux system, complete with the kernel, firmware, and bootloader, and is governed by the standard Red Hat Enterprise Linux end user license agreement. Universal base image is a smaller set of Red Hat Enterprise Linux packages under a more permissive license agreement that allows for redistribution. Its primary use is as a base for building application containers, aligning with the Red Hat Enterprise Linux lifecycle. Currently, making universal base images directly bootable by adding a kernel isn't supported.