Fix up node name resolution from within Pod

At present the hostname resolution is handed back the Pod name rather
than the node name when run within a Kubernetes deployment. We fix
this up by specifying a NODE_NAME environment variable and passing
it in - falling back to hostname lookup if it's unset, as in e.g.
node-local testing outside of a deployment context.

Author: pmundt

Dockerfile

@@ -1,6 +1,7 @@
 FROM golang as builder
 
 ARG KUBECONFIG
+ARG NODE_NAME
 
 ENV GO111MODULE=on
 

README.md

@@ -50,6 +50,7 @@ $ go get github.com/adaptant-labs/k8s-dt-node-labeller
 ```
 
 For Docker containers and Kubernetes deployment instructions, see below.
+
 ## Usage
 
 General usage is as follows:

controller.go

@@ -21,7 +21,7 @@ type reconcileNodeLabels struct {
 var _ reconcile.Reconciler = &reconcileNodeLabels{}
 
 func (r *reconcileNodeLabels) Reconcile(request reconcile.Request) (reconcile.Result, error) {
-	// set up a convinient log object so we don't have to type request over and over again
+	// set up a convenient log object so we don't have to type request over and over again
 	log := r.log.WithValues("request", request)
 
 	node := &corev1.Node{}

k8s-dt-labeller-ds.yaml

@@ -50,7 +50,12 @@ spec:
       nodeSelector:
         kubernetes.io/arch: arm64
       containers:
-      - image: adaptant/k8s-dt-node-labeller:latest
+      - env:
+          - name: NODE_NAME
+            valueFrom:
+              fieldRef:
+                fieldPath: spec.nodeName
+        image: adaptant/k8s-dt-node-labeller:latest
         name: dt-labeller
         securityContext:
           # Needed for /sys/firmware access

k8s-dt-labeller-nfd.yaml

@@ -60,7 +60,12 @@ spec:
       nodeSelector:
           kubernetes.io/arch: arm64
       initContainers:
-        - image: adaptant/k8s-dt-node-labeller:latest
+        - env:
+            - name: NODE_NAME
+              valueFrom:
+                fieldRef:
+                  fieldPath: spec.nodeName
+          image: adaptant/k8s-dt-node-labeller:latest
           name: dt-labeller
           args:
             - "-f"

main.go

@@ -157,6 +157,19 @@ func appendNodesIfNotExist(nodes[] string, names ...string) []string {
 	return nodes
 }
 
+func getNodeName() (string, error) {
+	// Within the Kubernetes Pod, the hostname provides the Pod name, rather than the node name, so we pass in the
+	// node name via the NODE_NAME environment variable instead.
+	nodeName := os.Getenv("NODE_NAME")
+	if len(nodeName) > 0 {
+		return nodeName, nil
+	}
+
+	// If the NODE_NAME environment variable is unset, fall back on hostname matching (e.g. when running outside of
+	// a Kubernetes deployment).
+	return os.Hostname()
+}
+
 func main() {
 	var n string
 	var d bool
@@ -245,7 +258,7 @@ func main() {
 	// tagged as part of the node's metadata.
 	pred := predicate.Funcs{
 		CreateFunc: func(e event.CreateEvent) bool {
-			hostname, err := os.Hostname()
+			hostname, err := getNodeName()
 			if err != nil {
 				return false
 			}