Tools: Latest Bootc And Ostree: Modernizing Linux System Deployment

For several years, I’ve been looking to manage my system configuration “As-code” to ensure reproducibility and consistency across my environments. The primary goal was to install my work laptop, but I also need to install Linux servers (without Kubernetes, so Talos isn’t an option).

Initially, I used Packer to generate a virtual machine image, which I would then clone onto the disk of the machine I wanted to configure. It worked very well for server templates, but for a dev machine, it was a bit of a patchwork solution. On top of that, I decided to look for a Packer alternative because of Hashicorp’s licensing changes (a decision I still struggle to accept!).

NixOS was an excellent replacement for a while, but I ran into several problems without having the necessary skills to solve them. I migrated to Fedora Silverblue, another immutable distribution in which I have more confidence. I found the comfort of a classic Linux installation while benefiting from the advantages of an immutable system.

Quick side-note: I’ll be talking a lot about OSTree in the context of CoreOS and Fedora Silverblue, but this technology isn’t exclusive to these distributions. We can also mention Fedora CoreOS, Endless OS, and even Podman’s virtual machine when on macOS or Windows.

But I feel like I’m getting ahead of myself, so let’s start at the beginning.

OSTree is often described as “Git for filesystems”. It enables versioning, distribution, and atomic deployment of Linux systems. Rather than managing packages individually, OSTree stores complete system snapshots, making updates and rollbacks easier.

It’s based on ComposeFS, whose primary focus is ensuring data integrity. It relies on EROFS (Enhanced Read-Only File System) to guarantee that data won’t be corrupted and to store file metadata. It natively performs data deduplication and LZ4 compression.

lowerdir is the read-only directory (composefs) containing file metadata, and datadir is the directory containing the data (erofs).

The data (in /sysroot/ostree/repo/objects) is stored in a dedicated directory that contains all system versions. Each version is identified by a hash, similar to Git.

The comparison with Git doesn’t stop there - OSTree allows you to create commits, new versions of our system, and switch between these versions just like you would with Git commits (git commit and git checkout).

Source: HackerNews