Merge pull request kubernetes#30 from Random-Liu/get-node-name-from-downward-api

NPD: Get node name from the downward api.

Author: dchen1107

Makefile

@@ -1,6 +1,6 @@
 all: push
 
-# See pod.yaml for the version currently running-- bump this ahead before rebuilding!
+# See node-problem-detector.yaml for the version currently running-- bump this ahead before rebuilding!
 TAG = v0.2
 
 PROJ = google_containers

README.md

@@ -73,14 +73,10 @@ spec:
         securityContext:
           privileged: true
         env:
-        - name: POD_NAME
+        - name: NODE_NAME
           valueFrom:
             fieldRef:
-              fieldPath: metadata.name
-        - name: POD_NAMESPACE
-          valueFrom:
-            fieldRef:
-              fieldPath: metadata.namespace
+              fieldPath: spec.nodeName
         volumeMounts:
         - name: log
           mountPath: /log

node-problem-detector.yaml

@@ -18,14 +18,10 @@ spec:
         securityContext:
           privileged: true
         env:
-        - name: POD_NAME
+        - name: NODE_NAME
           valueFrom:
             fieldRef:
-              fieldPath: metadata.name
-        - name: POD_NAMESPACE
-          valueFrom:
-            fieldRef:
-              fieldPath: metadata.namespace
+              fieldPath: spec.nodeName
         volumeMounts:
         - name: log
           mountPath: /log

pkg/problemclient/problem_client.go

@@ -57,15 +57,23 @@ func NewClientOrDie() Client {
 	}
 	// TODO(random-liu): Set QPS Limit
 	c.client = client.NewOrDie(cfg)
-	// Get node name from the current pod.
-	pod, err := c.client.Pods(os.Getenv("POD_NAMESPACE")).Get(os.Getenv("POD_NAME"))
-	if err != nil {
-		panic(err)
-	}
-	if pod.Spec.NodeName == "" {
-		panic("empty node name")
+	// Get node name from environment variable NODE_NAME
+	// By default, assume that the NODE_NAME env should have been set with
+	// downward api. We prefer it because sometimes the hostname returned
+	// by os.Hostname is not right because:
+	// 1. User may override the hostname.
+	// 2. For some cloud providers, os.Hostname is different from the real hostname.
+	c.nodeName = os.Getenv("NODE_NAME")
+	if c.nodeName == "" {
+		// For backward compatibility. If the env is not set, get the hostname
+		// from os.Hostname(). This may not work for all configurations and
+		// environments.
+		var err error
+		c.nodeName, err = os.Hostname()
+		if err != nil {
+			panic("empty node name")
+		}
 	}
-	c.nodeName = pod.Spec.NodeName
 	c.nodeRef = getNodeRef(c.nodeName)
 	c.recorders = make(map[string]record.EventRecorder)
 	return c