cli/cmd: make health return error instead of using Fatalf

To soften the dependency on log.Entry and to separate the functionality
from CLI code. This also makes code easier to move around and avoids
hiding function complexity.

Part of #630

Signed-off-by: Mateusz Gozdek <mateusz@kinvolk.io>

cli/cmd/health.go

@@ -49,24 +49,32 @@ func runHealth(cmd *cobra.Command, args []string) {
 		log.SetLevel(log.DebugLevel)
 	}
 
+	if err := health(contextLogger); err != nil {
+		contextLogger.Fatalf("Checking cluster health failed: %v", err)
+	}
+}
+
+//nolint:funlen
+func health(contextLogger *log.Entry) error {
 	lokoConfig, diags := getLokoConfig()
 	if diags.HasErrors() {
 		for _, diagnostic := range diags {
 			contextLogger.Error(diagnostic.Error())
 		}
 
-		contextLogger.Fatal("Errors found while loading cluster configuration")
+		return diags
 	}
 
 	kubeconfig, err := getKubeconfig(contextLogger, lokoConfig, true)
 	if err != nil {
 		contextLogger.Debugf("Error in finding kubeconfig file: %s", err)
-		contextLogger.Fatal("Suitable kubeconfig file not found. Did you run 'lokoctl cluster apply' ?")
+
+		return fmt.Errorf("suitable kubeconfig file not found. Did you run 'lokoctl cluster apply' ?")
 	}
 
 	cs, err := k8sutil.NewClientset(kubeconfig)
 	if err != nil {
-		contextLogger.Fatalf("Error in creating Kubernetes client: %q", err)
+		return fmt.Errorf("creating Kubernetes client: %w", err)
 	}
 
 	// We can skip error checking here, as getKubeconfig() already checks it.
@@ -76,18 +84,18 @@ func runHealth(cmd *cobra.Command, args []string) {
 
 	ns, err := cluster.GetNodeStatus()
 	if err != nil {
-		contextLogger.Fatalf("Error getting node status: %q", err)
+		return fmt.Errorf("getting node status: %w", err)
 	}
 
 	ns.PrettyPrint()
 
 	if !ns.Ready() {
-		contextLogger.Fatalf("The cluster is not completely ready.")
+		return fmt.Errorf("cluster is not completely ready")
 	}
 
 	components, err := cluster.Health()
 	if err != nil {
-		contextLogger.Fatalf("Error in getting Lokomotive cluster health: %q", err)
+		return fmt.Errorf("getting Lokomotive cluster health: %w", err)
 	}
 
 	w := tabwriter.NewWriter(os.Stdout, 0, 0, 4, ' ', 0)
@@ -114,4 +122,6 @@ func runHealth(cmd *cobra.Command, args []string) {
 
 		w.Flush()
 	}
+
+	return nil
 }