Flatcar Linux 101
A Hands-Free Server OS
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# What is Flatcar Linux?
A container-optimized Linux distribution
- Made for running containers - focused on doing this and only this well
- Orchestrated: Kubernetes worker nodes, other orchestration systems
- Unorchestrated: Docker Compose, Podman, standalone containers
- Think of the OS itself as being treated like a container image
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# Flatcar is a CNCF Project
CoreOS → Kinvolk → Microsoft → CNCF
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# Functionality, not Features
General-purpose Linux | Flatcar
:--|:--
Choose your shell, desktop, language stack | We choose for you
Manage updates: backports vs. new repos vs. waiting | Whole OS updates atomically
Think about *features*: this version, this package | Think about *functionality*: does it work?
You build the system you want | We deliver a light switch
Components may shift under your feet | Contract: runtime stays the same
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# Provisioned, not Installed
| Install | Provision |
|:--|:--|
| Make choices during setup | Declare what you need up front |
| Interactive process | One declarative configuration |
| Each machine slightly different | Every machine identical |
Same idea as containers: you don't bake config into the image — you write config and apply it at launch.
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# Immutable by Design
- First boot: provisioned from config. After that: the base OS doesn't change.
- `/usr` is read-only and dm-verity protected
- No individual package updates — the entire OS updates as one unit
- Same config + same base OS = identical machine every time
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# Demo: Provisioning a Server
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# A/B Updates
```
┌──────────────┐ ┌──────────────┐
│ Partition A │ │ Partition B │
│ (running) │ │ (staging) │
└──────────────┘ └──────────────┘
↕ reboot ↕
```
- Verified image staged to inactive partition
- Reboot activates the new OS
- Rollback = reboot to old partition
- No intermediate states — it works or it rolls back
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# Channels
```
Alpha → Beta → Stable (+ LTS)
```
- **Alpha**: Fully tested, may have incomplete features. For developers.
- **Beta**: Production-ready. Run as canaries alongside stable.
- **Stable**: Widespread production. Promoted from beta.
- **LTS**: Long-term support track for environments that need slower change.
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# Demo: systemd-sysext
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# Flatcar Runs Everywhere
| Environment | Options |
|:--|:--|
| **Cloud** | Azure, AWS, GCP, and many more |
| **Virtualization** | VMware, VirtualBox, libvirt, QEMU |
| **Bare metal** | PXE / iPXE |
Also: Terraform, Go bindings, Cluster API
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# Try It Today — Get Involved
| Community | Try It Locally |
|:--|:--|
| **flatcar.org** — website & docs | 1. Download the QEMU image from flatcar.org |
| **Chat**: Matrix · CNCF Slack | 2. Write a Butane YAML config |
| **GitHub Discussions** | 3. Transpile: `butane config.bu > config.ign` |
| **Office Hours**: every 2nd Tue, 15:30 UTC | 4. Boot: `./flatcar_production_qemu.sh -i config.ign` |
| **DevSync**: every 4th Tue, 15:30 UTC | |
| **Bug Smash**: last Fri of the month | ~5 minutes to a running system |
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# Thank You
**Visit Flatcar** → flatcar.org
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