Chapter 11. Managing RHEL bootc images

You can change the container image reference used for upgrades by using the bootc switch command. For example, you can switch from the stage to the production tag. To manually switch an existing ostree-based container image reference, use the bootc switch command.

The rhel10/rhel-bootc image uses the dracut infrastructure to build an initial RAM disk (initrd) during the image build time. A default initrd is built and included in the /usr/lib/modules/<kernel_version>/initramfs.img location inside the container image. You can use a drop-in configuration file to extend the dracut configuration, and place it in a file in the /usr/lib/dracut/dracut.conf.d/ directory. This re-creates `initrd with the modules you want to add.

With image mode for RHEL, you can perform any other management task, such as changing or updating the system, by pushing the changes to the container registry.

When using image mode for RHEL, you can choose to perform manual updates for your systems. If you have automatic updates enabled, you must turn them off to perform a manual update. To do so, use one of the following options:

You can roll back to a previous boot entry to revert changes in the system by using the bootc rollback command. This command changes the boot loader entry ordering by making the deployment under rollback queued for the next boot. The current deployment then becomes the rollback. Any staged changes, such as a queued upgrade that was not applied, are discarded.

After a rollback completes, the system reboots and the update timer run within 1 to 3 hours which automatically update and reboot your system to the image you just rolled back from.

When performing a rollback, for example, by using the bootc rollback command, changes made to files in the /etc directory do not carry over to the rolled-back deployment. Instead, the files in the /etc directory revert to the state they were in during the previous deployment.

The bootc rollback command reorders existing deployments but does not create new ones. The /etc directory is merged when new deployments are created.

To preserve a modified /etc file for use after a rollback, copy it to a directory under /var, such as /var/home/<user> for a specific <user>, or under /var/root/, for the root user. These directories are unaffected by rollbacks, as they store user content.

When returning to the original state, either through a temporary rollback or another bootc rollback, the /etc directory reverts to its state from the original deployment.

Alternatively, if the issue you are rolling back does not involve configuration files in the /etc directory and you want to revert to an older deployment, use the bootc switch command. This command performs the necessary /etc merge and deploy the previous version of the software.

You can change the configuration of your operating system by modifying the Containerfile. The update will be applied after you build and push your container image to the registry, and reboot the operating system.

You can also change the container image source by using the bootc switch command. The content in the container registry determines the specific configuration of the RHEL Image Mode operating system. See Switching the container image reference.

Usually, when deploying updates to system groups, you can use a central management service to provide a client to be installed on each system which connects to the central service. Often, the management service requires the client to perform a one time registration. The following is an example on how to deploy updates to system groups. You can modify, by injecting the credentials for the management service into the image, to create a persistent systemd service, if required.

You can install a client into a image mode for RHEL image and run it at startup to register the system.

Assess the status of your Red Hat Enterprise Linux managed nodes to verify they are online and reachable. Checking inventory health ensures that your systems are ready to receive updates or configuration changes without interruption. You can manually check the system health of the container images and events that are running inside the container.

You can use CI/CD (Continuous Integration and Continuous Delivery) pipelines to automate the building process of your RHEL bootc images. By using a CI/CD , an event can trigger an update, such as updating an application.

You can use automation tools that track these updates and trigger the CI/CD pipelines, such as GitHub Actions, and GitLab CI. The pipeline keeps the systems up to date by using the transactional background operating system updates.

For more details on resources to create image mode for RHEL instances, check the specific implementations available to create image mode for RHEL instances:RHEL Image Mode CI/CD.