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Ignition

Ignition is a system for declaratively provisioning disks during the initramfs, before systemd starts. It runs only on the first boot and handles formatting partitions, writing files (systemd units, networkd units, dropins, regular files), and configuring users. See the Ignition docs for details.

Ignition template files can be added in an ignition subdirectory of the bootcfg data directory. The files may contain Go template elements which should evaluate, with metadata, to Ignition JSON or to Ignition YAML (which will be rendered as JSON).

data
 ├── cloud
 ├── ignition
 │   └── simple.json
 │   └── etcd.yaml
 │   └── etcd_proxy.yaml
 │   └── networking.yaml
 └── specs

Add an Ignition config to a Spec by adding the ignition_id field. When PXE booting, use the kernel option coreos.first_boot=1 and coreos.config.url to point to the bootcfgignition endpoint.

spec.json:

 {
     "id": "etcd_profile",
     "boot": {
         "kernel": "/assets/coreos/899.6.0/coreos_production_pxe.vmlinuz",
         "initrd": ["/assets/coreos/899.6.0/coreos_production_pxe_image.cpio.gz"],
         "cmdline": {
             "coreos.config.url": "http://bootcfg.foo/ignition?uuid=${uuid}&mac=${net0/mac:hexhyp}",
             "coreos.first_boot": "1"
         }
     },
     "cloud_id": "",
     "ignition_id": "etcd.yaml"
 }

Configs

Here is an example Ignition config for static networking, which will be evaluated with metadata into YAML and tranformed into machine-friendly JSON.

ignition/network.yaml:

---
ignition_version: 1
networkd:
  units:
    - name: 00-{{.networkd_name}}.network
      contents: |
        [Match]
        Name={{.networkd_name}}
        [Network]
        Gateway={{.networkd_gateway}}
        DNS={{.networkd_dns}}
        DNS=8.8.8.8
        Address={{.networkd_address}}
{{ if .ssh_authorized_keys }}
passwd:
  users:
    - name: core
      ssh_authorized_keys:
        {{ range $element := .ssh_authorized_keys }}
        - {{$element}}
        {{end}}
{{end}}

Response from /ignition?mac=address for a particular machine.

{
  "ignitionVersion": 1,
  "storage": {},
  "systemd": {},
  "networkd": {
    "units": [
      {
        "name": "00-ens3.network",
        "contents": "[Match]\nName=ens3\n[Network]\nGateway=172.15.0.1\nDNS=172.15.0.3\nDNS=8.8.8.8\nAddress=172.15.0.21/16\n"
      }
    ]
  },
  "passwd": {}
}

Note that Ignition does not allow variables - the response has been fully rendered with metadata for the requesting machine.

Ignition configs can be provided directly as JSON as well. This is useful for simple cases or if you prefer to use your own templating solution to generate Ignition configs.

ignition/run-hello.json:

{
    "ignitionVersion": 1,
    "systemd": {
        "units": [
            {
                "name": "hello.service",
                "enable": true,
                "contents": "[Service]\nType=oneshot\nExecStart=/usr/bin/echo Hello World\n\n[Install]\nWantedBy=multi-user.target"
            }
        ]
    }
}

Examples

See examples/ignition for example Ignition configs which setup networking, install CoreOS to disk, or start etcd.

Endpoint

The bootcfg Ignition endpoint /ignition?param=val endpoint matches parameters to a machine Spec and renders the corresponding Ignition config with metadata, transforming YAML to JSON if needed.