From f406206eaeaa68959a1a0725d4722a297ab62c8e Mon Sep 17 00:00:00 2001
From: TwinProduction <twin@twinnation.org>
Date: Wed, 11 Nov 2020 15:10:44 -0500
Subject: [PATCH] Create type ClusterMode string and panic only in the config
 validation function

---
 config/config.go |  7 +++++--
 k8s/client.go    | 42 ++++++++++++++++++------------------------
 k8s/config.go    | 12 ++++++++++--
 k8s/discovery.go |  5 ++++-
 4 files changed, 37 insertions(+), 29 deletions(-)

diff --git a/config/config.go b/config/config.go
index 0cb1c9de..1ffb71c8 100644
--- a/config/config.go
+++ b/config/config.go
@@ -116,8 +116,8 @@ func parseAndValidateConfigBytes(yamlBytes []byte) (config *Config, err error) {
 	if err != nil {
 		return
 	}
-	// Check if the configuration file at least has services.
-	if config == nil || config.Services == nil || len(config.Services) == 0 {
+	// Check if the configuration file at least has services configured or Kubernetes auto discovery enabled
+	if config == nil || ((config.Services == nil || len(config.Services) == 0) && (config.Kubernetes == nil || !config.Kubernetes.AutoDiscover)) {
 		err = ErrNoServiceInConfig
 	} else {
 		// Note that the functions below may panic, and this is on purpose to prevent Gatus from starting with
@@ -132,6 +132,9 @@ func parseAndValidateConfigBytes(yamlBytes []byte) (config *Config, err error) {
 
 func validateKubernetesConfig(config *Config) {
 	if config.Kubernetes != nil && config.Kubernetes.AutoDiscover {
+		if config.Kubernetes.ServiceTemplate == nil {
+			panic("kubernetes.service-template cannot be nil")
+		}
 		discoveredServices, err := k8s.DiscoverServices(config.Kubernetes)
 		if err != nil {
 			panic(err)
diff --git a/k8s/client.go b/k8s/client.go
index 9aa5c421..bcb5fed8 100644
--- a/k8s/client.go
+++ b/k8s/client.go
@@ -2,6 +2,7 @@ package k8s
 
 import (
 	"flag"
+	"fmt"
 	"os"
 	"path/filepath"
 
@@ -11,21 +12,22 @@ import (
 	"k8s.io/client-go/tools/clientcmd"
 )
 
-func NewClient(clusterMode string) *kubernetes.Clientset {
+// NewClient creates a Kubernetes client for the given ClusterMode
+func NewClient(clusterMode ClusterMode) (*kubernetes.Clientset, error) {
 	var kubeConfig *rest.Config
+	var err error
 	switch clusterMode {
-	case "in":
-		kubeConfig = getInClusterConfig()
-	case "out":
-		kubeConfig = getOutClusterConfig()
+	case ClusterModeIn:
+		kubeConfig, err = getInClusterConfig()
+	case ClusterModeOut:
+		kubeConfig, err = getOutClusterConfig()
 	default:
-		panic("invalid cluster mode")
+		return nil, fmt.Errorf("invalid cluster mode, try '%s' or '%s'", ClusterModeIn, ClusterModeOut)
 	}
-	clientset, err := kubernetes.NewForConfig(kubeConfig)
 	if err != nil {
-		panic(err.Error())
+		return nil, fmt.Errorf("unable to get cluster config for mode '%s': %s", clusterMode, err.Error())
 	}
-	return clientset
+	return kubernetes.NewForConfig(kubeConfig)
 }
 
 func homeDir() string {
@@ -35,25 +37,17 @@ func homeDir() string {
 	return os.Getenv("USERPROFILE") // windows
 }
 
-func getOutClusterConfig() *rest.Config {
-	var kubeconfig *string
+func getOutClusterConfig() (*rest.Config, error) {
+	var kubeConfig *string
 	if home := homeDir(); home != "" {
-		kubeconfig = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "(optional) absolute path to the kubeconfig file")
+		kubeConfig = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "(optional) absolute path to the kubeconfig file")
 	} else {
-		kubeconfig = flag.String("kubeconfig", "", "absolute path to the kubeconfig file")
+		kubeConfig = flag.String("kubeconfig", "", "absolute path to the kubeconfig file")
 	}
 	flag.Parse()
-	config, err := clientcmd.BuildConfigFromFlags("", *kubeconfig)
-	if err != nil {
-		panic(err.Error())
-	}
-	return config
+	return clientcmd.BuildConfigFromFlags("", *kubeConfig)
 }
 
-func getInClusterConfig() *rest.Config {
-	config, err := rest.InClusterConfig()
-	if err != nil {
-		panic(err.Error())
-	}
-	return config
+func getInClusterConfig() (*rest.Config, error) {
+	return rest.InClusterConfig()
 }
diff --git a/k8s/config.go b/k8s/config.go
index aa7abd54..2b4679ed 100644
--- a/k8s/config.go
+++ b/k8s/config.go
@@ -10,11 +10,11 @@ type Config struct {
 	// ServiceTemplate Template for auto discovered services
 	ServiceTemplate *core.Service `yaml:"service-template"`
 
-	// ExcludeSuffix Ignore services with this suffix
+	// ExcludeSuffix is a slice of service suffixes that should be ignored
 	ExcludeSuffix []string `yaml:"exclude-suffix"`
 
 	// ClusterMode to authenticate with kubernetes
-	ClusterMode string `yaml:"cluster-mode"`
+	ClusterMode ClusterMode `yaml:"cluster-mode"`
 
 	// Namespaces from which to discover services
 	Namespaces []*NamespaceConfig `yaml:"namespaces"`
@@ -31,3 +31,11 @@ type NamespaceConfig struct {
 	// HealthAPI URI to append to service to reach health check API
 	HealthAPI string `yaml:"health-api"`
 }
+
+// ClusterMode is the mode to use to authenticate to Kubernetes
+type ClusterMode string
+
+const (
+	ClusterModeIn  ClusterMode = "in"
+	ClusterModeOut ClusterMode = "out"
+)
diff --git a/k8s/discovery.go b/k8s/discovery.go
index 947459e3..4e71df39 100644
--- a/k8s/discovery.go
+++ b/k8s/discovery.go
@@ -9,7 +9,10 @@ import (
 
 // DiscoverServices return discovered services
 func DiscoverServices(kubernetesConfig *Config) ([]*core.Service, error) {
-	client := NewClient(kubernetesConfig.ClusterMode)
+	client, err := NewClient(kubernetesConfig.ClusterMode)
+	if err != nil {
+		return nil, err
+	}
 	services := make([]*core.Service, 0)
 	for _, ns := range kubernetesConfig.Namespaces {
 		kubernetesServices, err := GetKubernetesServices(client, ns.Name)