docs: Add README with node configuration

README.md

@@ -0,0 +1,40 @@
+# gitops
+
+Argo CD manifests for a single-node k3s cluster.
+
+## Node configuration
+
+These live on the node, not in this repo, so reapply them when rebuilding it.
+
+### k3s
+
+The bundled Traefik is replaced by the Argo CD-managed one, which is exposed
+via `externalIPs` rather than ServiceLB. Control-plane metrics endpoints are
+exposed for Prometheus:
+
+```yaml
+# /etc/rancher/k3s/config.yaml
+disable:
+  - traefik
+  - servicelb
+kube-controller-manager-arg:
+  - bind-address=0.0.0.0
+kube-scheduler-arg:
+  - bind-address=0.0.0.0
+kube-proxy-arg:
+  - metrics-bind-address=0.0.0.0
+```
+
+### Image garbage collection
+
+Kubelet only prunes images once the disk crosses 85%, so unused images pile up
+on a large disk. Also expire images that haven't been used in 7 days:
+
+```yaml
+# /var/lib/rancher/k3s/agent/etc/kubelet.conf.d/50-image-gc.conf
+apiVersion: kubelet.config.k8s.io/v1beta1
+kind: KubeletConfiguration
+imageMaximumGCAge: 168h
+```
+
+Apply with `sudo systemctl restart k3s`.