examples/ignition/bootkube: Wrap bootkube in systemd service

* Start `bootkube start` via systemctl, don't require a persistent
SSH connection during the script run

Documentation/bootkube.md

@@ -63,10 +63,11 @@ Secure copy the `kubeconfig` to `/etc/kubernetes/kubeconfig` on **every** node w
 Secure copy the `bootkube` generated assets to any controller node and run `bootkube-start`.
 
     scp -r assets core@node1.example.com:/home/core/assets
-    ssh core@node1.example.com 'sudo ./bootkube-start'
+    ssh core@node1.example.com 'sudo systemctl start bootkube'
 
-Watch the temporary control plane logs until the scheduled kubelet takes over in place of the on-host kubelet.
+Optionally watch the Kubernetes control plane bootstrapping with the bootkube temporary api-server. You will see quite a bit of output.
 
+    $ ssh core@node1.example.com 'journalctl -f -u bootkube'
     [  299.241291] bootkube[5]:     Pod Status:     kube-api-checkpoint     Running
     [  299.241618] bootkube[5]:     Pod Status:          kube-apiserver     Running
     [  299.241804] bootkube[5]:     Pod Status:          kube-scheduler     Running

examples/ignition/bootkube-controller.yaml

@@ -77,7 +77,13 @@ systemd:
         RestartSec=10
         [Install]
         WantedBy=multi-user.target
-
+    - name: bootkube.service
+      contents: |
+        [Unit]
+        Description=Bootstrap a Kubernetes control plane with a temp api-server
+        [Service]
+        Type=simple
+        ExecStart=/home/core/bootkube-start
 storage:
   {{ if index . "pxe" }}
   disks: