feat: Configure Prometheus endpoint via Helm chart (#4562)

Add PrometheusEndpoint to backend config and API
- Update frontend to use configured endpoint for Prometheus plugin
- Add config.prometheus.endpoint to Helm chart values
- Use safe quoting for Helm value injection
- Add backend validation for Prometheus URL

Signed-off-by: zyzzmohit <mohitray949@gmail.com>

Author: zyzzmohit

backend/cmd/headlamp.go

@@ -97,6 +97,7 @@ const (
 type clientConfig struct {
 	Clusters                []Cluster `json:"clusters"`
 	IsDynamicClusterEnabled bool      `json:"isDynamicClusterEnabled"`
+	PrometheusEndpoint      string    `json:"prometheusEndpoint"`
 }
 
 type OauthConfig struct {
@@ -1750,7 +1751,7 @@ func parseClusterFromKubeConfig(kubeConfigs []string) ([]Cluster, []error) {
 func (c *HeadlampConfig) getConfig(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "application/json")
 
-	clientConfig := clientConfig{c.getClusters(), c.EnableDynamicClusters}
+	clientConfig := clientConfig{c.getClusters(), c.EnableDynamicClusters, c.PrometheusEndpoint}
 
 	if err := json.NewEncoder(w).Encode(&clientConfig); err != nil {
 		logger.Log(logger.LevelError, nil, err, "encoding config")

backend/cmd/server.go

@@ -101,6 +101,7 @@ func buildHeadlampCFG(conf *config.Config, kubeConfigStore kubeconfig.ContextSto
 		TLSCertPath:           conf.TLSCertPath,
 		TLSKeyPath:            conf.TLSKeyPath,
 		SessionTTL:            conf.SessionTTL,
+		PrometheusEndpoint:    *conf.PrometheusEndpoint,
 	}
 }
 

backend/cmd/stateless.go

@@ -178,7 +178,7 @@ func (c *HeadlampConfig) parseKubeConfig(w http.ResponseWriter, r *http.Request)
 		return
 	}
 
-	clientConfig := clientConfig{contexts, c.EnableDynamicClusters}
+	clientConfig := clientConfig{contexts, c.EnableDynamicClusters, c.PrometheusEndpoint}
 
 	if err := json.NewEncoder(w).Encode(&clientConfig); err != nil {
 		logger.Log(logger.LevelError, nil, err, "encoding config")

backend/pkg/config/config.go

@@ -85,6 +85,7 @@ type Config struct {
 	// TLS config
 	TLSCertPath string `koanf:"tls-cert-path"`
 	TLSKeyPath  string `koanf:"tls-key-path"`
+	PrometheusEndpoint *string `koanf:"prometheus-endpoint"`
 }
 
 func (c *Config) Validate() error {
@@ -144,6 +145,12 @@ func (c *Config) Validate() error {
 		}
 	}
 
+	if c.PrometheusEndpoint != nil && *c.PrometheusEndpoint != "" {
+		if !strings.HasPrefix(*c.PrometheusEndpoint, "http://") && !strings.HasPrefix(*c.PrometheusEndpoint, "https://") {
+			return errors.New("prometheus-endpoint must start with http:// or https://")
+		}
+	}
+
 	return nil
 }
 
@@ -448,6 +455,7 @@ func addGeneralFlags(f *flag.FlagSet) {
 	f.Uint("port", defaultPort, "Port to listen from")
 	f.String("proxy-urls", "", "Allow proxy requests to specified URLs")
 	f.Bool("enable-helm", false, "Enable Helm operations")
+	f.String("prometheus-endpoint", "", "Prometheus endpoint for the cluster")
 }
 
 func addOIDCFlags(f *flag.FlagSet) {

backend/pkg/headlampconfig/headlampConfig.go

@@ -63,4 +63,5 @@ type HeadlampCFG struct {
 	TLSCertPath           string
 	TLSKeyPath            string
 	SessionTTL            int
+	PrometheusEndpoint    string
 }

backend/pkg/kubeconfig/kubeconfig_test.go

@@ -10,7 +10,6 @@ import (
 	"path/filepath"
 	"testing"
 
-	"github.com/kubernetes-sigs/headlamp/backend/pkg/config"
 	"github.com/kubernetes-sigs/headlamp/backend/pkg/kubeconfig"
 	"github.com/pkg/errors"
 	"github.com/stretchr/testify/assert"
@@ -315,11 +314,44 @@ func createTempKubeconfig(t *testing.T, content string) string {
 }
 
 func TestContext(t *testing.T) {
-	kubeConfigFile := config.GetDefaultKubeConfigPath()
+	// Start a mock server
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/version" {
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(`{"major": "1", "minor": "20"}`))
+			return
+		}
+		w.WriteHeader(http.StatusNotFound)
+	}))
+	defer server.Close()
+
+	// Create a temp kubeconfig pointing to the mock server
+	kubeConfigContent := fmt.Sprintf(`apiVersion: v1
+clusters:
+- cluster:
+    server: %s
+    insecure-skip-tls-verify: true
+  name: minikube
+contexts:
+- context:
+    cluster: minikube
+    namespace: default
+    user: minikube
+  name: minikube
+current-context: minikube
+kind: Config
+users:
+- name: minikube
+  user:
+    token: test-token
+`, server.URL)
+
+	tempFile := createTempKubeconfig(t, kubeConfigContent)
+	defer os.Remove(tempFile)
 
 	configStore := kubeconfig.NewContextStore()
 
-	err := kubeconfig.LoadAndStoreKubeConfigs(configStore, kubeConfigFile, kubeconfig.KubeConfig, nil)
+	err := kubeconfig.LoadAndStoreKubeConfigs(configStore, tempFile, kubeconfig.KubeConfig, nil)
 	require.NoError(t, err)
 
 	testContext, err := configStore.GetContext("minikube")
@@ -342,6 +374,11 @@ func TestContext(t *testing.T) {
 
 	err = testContext.ProxyRequest(rr, request)
 	require.NoError(t, err)
+	// We need to flush the proxy response to the recorder
+	if f, ok := rr.Result().Body.(http.Flusher); ok {
+		f.Flush()
+	}
+
 	assert.Equal(t, http.StatusOK, rr.Code)
 
 	t.Logf("Proxy request Response: %s", rr.Body.String())