Migrate hand-written quadlets¶

A host that already runs hand-written quadlet files can be moved to syslet unit by unit: each file becomes a spec with the same options. The containers keep running until the first apply restarts them.

Translate each file into a spec¶

The file name without its extension becomes the spec name, and each section becomes a struct under unit. An option that appears several times becomes a list:

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[Container]
Image=docker.io/library/nginx:1.27
PublishPort=8080:80
PublishPort=8443:443
Volume=webapp-data.volume:/data

[Install]
WantedBy=multi-user.target

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sysdef: containers: webapp: spec: {
    unit: Container: {
        Image: "docker.io/library/nginx:1.27"
        PublishPort: ["8080:80", "8443:443"]
        Volume: ["systemd-webapp-data.volume:/data"]
    }
}

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{
  "apiVersion": "v1",
  "type": "container",
  "name": "webapp",
  "desiredState": "running",
  "unit": {
    "Container": {
      "Image": "docker.io/library/nginx:1.27",
      "PublishPort": ["8080:80", "8443:443"],
      "Volume": ["systemd-webapp-data.volume:/data"]
    }
  }
}

Leave out [Install] WantedBy= and [Service] Restart=; desiredState: "running" sets both. syslet only manages .container, .volume, .network and .build files; leave other types, such as .pod or .kube, as they are.

Keep the names that matter¶

Quadlet names a resource systemd-<file name> unless the file sets a name; syslet always names it after the spec, without the prefix. Check the existing names with podman ps -a, podman volume ls and podman network ls:

• Volumes hold data. Name the volume spec after the existing podman volume, here systemd-webapp-data, so it's reused (see Adopt an existing volume), and lock it.
• Containers get new names. Update containers that reach each other by name, and scripts that use podman exec.
• Networks are created again under the new name. Delete the old ones with podman network rm once nothing uses them.

Drop ContainerName=, VolumeName= and NetworkName= from the specs; syslet overwrites them.

Hand over the host¶

Move the hand-written files out of the quadlet directory and reload systemd:

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sudo mkdir /root/quadlets-old
sudo mv /etc/containers/systemd/*.{container,volume,network,build} /root/quadlets-old/
sudo systemctl daemon-reload

The containers keep running. syslet sees that their services are still active and restarts them onto the new units on the first apply.

Preview and apply¶

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cue cmd plan

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cat hosts/web01/*.json | ssh web01 sudo syslet --diff --stdin

Every unit should show as created, and each running container under Services to stop: and Containers to start:. Apply, then check that the containers run and the volumes hold their data.

To back out before applying, move the files back and run systemctl daemon-reload.