Description

SME: gscrivan@redhat.com 

Image mode for RHEL leverages composefs as a foundational technology.  The composefs will be Tech Preview for this release, and will be used by bootc/imagemode

Goals

• Majority of users will not need to interact directly with this technology directly.
• Optimize page cache sharing across containers.
• Improve the "tamper proof" story of RHEL and gain dm-verity-like capabilities via fsverity
• Offer a higher degree of immutability for use cases that require it, e.g. RHIVOS
• Optimize disk usage (container & OS storage).
• Set a foundation that can be used to sealing & signing the OS and connect w/ secure boot.

Requirements

(Optional) Use Cases

< How will the user interact with this feature? >

We expect composefs to be largely an architectural component that will be transparent to most users. More advanced use cases and users will likely need documentation and knowledge to opt-in to more advanced capabilities.

Out of Scope

Secure boot and adding end user keys to firmware.

Background, and strategic fit

Composefs originates from the RHIVOS side of the house and solves a number of problems that mirrors the goals above in this feature. For more info on the project see this presentation. 

Assumptions

Basic use of Composefs will be implied with our base image, and once ready, podman may also default to using the composefs backend in the rhel-bootc image. We should assume that regardless of the default, podman's backing store will remain configurable for users. 

Customer Considerations

Composefs, and how the features are implemented in rhel-bootc, is not a one & done release. Customers should expect more capabilities to come online and be supported as we progress. 

Documentation Considerations

If the initial implementation ends up being transparent to the end users, then this will likely just be a release note. 

vsferity will require some documentation.