Clarify rest.Config construction

I was told this function was messy and unclear,
so let's try to make it a bit more explicit,
commented and straightfoward (hopefuly).

While at it, unhide issues at healthcheck server
start.

Author: bpineau

config/config.go

@@ -45,7 +45,7 @@ type KdnConfig struct {
 
 // Init initialize the config
 func (c *KdnConfig) Init(apiserver string, kubeconfig string) (err error) {
-	c.Client, err = client.BuildConfig(apiserver, kubeconfig)
+	c.Client, err = client.NewRestConfig(apiserver, kubeconfig)
 	if err != nil {
 		return fmt.Errorf("Failed init Kubernetes clientset: %+v", err)
 	}

pkg/client/client.go

@@ -1,4 +1,4 @@
-// Package client  initialize a Kubernete's client-go rest.Config
+// Package client  initialize a Kubernete's client-go rest.Config or clientset
 package client
 
 import (
@@ -14,31 +14,41 @@ import (
 	_ "k8s.io/client-go/plugin/pkg/client/auth/gcp"
 )
 
-// BuildConfig create a *rest.Config
-func BuildConfig(apiserver string, kubeconfig string) (*rest.Config, error) {
-	// if we're not provided a kubeconfig path, try to find one in user's home
+// NewRestConfig create a *rest.Config, using the kubectl paths and priorities:
+// - Command line flags (api-server and/or kubeconfig path) have higher priorities
+// - Else, use the config file path in KUBECONFIG environment variable, if any
+// - Else, use the config file in ~/.kube/config, if any
+// - Else, consider we're running in cluster (in a pod), and use the pod's service
+//   account and cluster's kubernetes.default service.
+func NewRestConfig(apiserver string, kubeconfig string) (*rest.Config, error) {
+	// if not passed as an argument, kubeconfig can be provided as env var
 	if kubeconfig == "" {
-		if home := homedir.HomeDir(); home != "" {
-			if _, err := os.Stat(filepath.Join(home, ".kube", "config")); err == nil {
-				kubeconfig = filepath.Join(home, ".kube", "config")
-			}
-		}
+		kubeconfig = os.Getenv("KUBECONFIG")
 	}
 
-	// if we're provided an api-server url, or found a kubeconfig file, use that
+	// if we're not provided an explicit kubeconfig path (via env, or argument),
+	// try to find one at the standard place (in user's home/.kube/config).
+	homeCfg := filepath.Join(homedir.HomeDir(), ".kube", "config")
+	_, err := os.Stat(homeCfg)
+	if kubeconfig == "" && err == nil {
+		kubeconfig = homeCfg
+	}
+
+	// if we were provided or found a kubeconfig,
+	// or if we were provided an api-server url, use that
 	if apiserver != "" || kubeconfig != "" {
 		return clientcmd.BuildConfigFromFlags(apiserver, kubeconfig)
 	}
 
-	// else assume we're running in cluster
+	// else assume we're running in a pod, in cluster
 	return rest.InClusterConfig()
 }
 
 // NewClientSet create a clientset (a client connection to a Kubernetes cluster).
 // It will connect using the optional apiserver or kubeconfig options, or will
 // default to the automatic, in cluster settings.
 func NewClientSet(apiserver string, kubeconfig string) (*kubernetes.Clientset, error) {
-	config, err := BuildConfig(apiserver, kubeconfig)
+	config, err := NewRestConfig(apiserver, kubeconfig)
 	if err != nil {
 		return nil, err
 	}

pkg/health/health.go

@@ -46,7 +46,10 @@ func (h *Listener) Start() (*Listener, error) {
 
 	go func() {
 		defer close(h.donech)
-		_ = h.srv.ListenAndServe()
+		err := h.srv.ListenAndServe()
+		if err != nil && err.Error() != "http: Server closed" {
+			h.config.Logger.Errorf("healthcheck server failed: %v", err)
+		}
 	}()
 
 	return h, nil