refactor: return error from NewHealthzHandlerWithChecks instead of panicking

Author: tyler-lloyd

cns/healthserver/healthz.go

@@ -1,7 +1,6 @@
 package healthserver
 
 import (
-"fmt"
 "net/http"
 
 "github.com/Azure/azure-container-networking/cns"
@@ -22,16 +21,20 @@ func init() {
 utilruntime.Must(v1alpha.AddToScheme(scheme))
 }
 
-func NewHealthzHandlerWithChecks(cnsConfig *configuration.CNSConfig) http.Handler {
+// NewHealthzHandlerWithChecks will return a [http.Handler] for CNS's /healthz endpoint.
+// Depending on what we expect CNS to be able to read (based on the [configuration.CNSConfig])
+// then the checks registered to the handler will test for those expectations. For example, in
+// ChannelMode: CRD, the health check will ensure that CNS is able to list NNCs successfully.
+func NewHealthzHandlerWithChecks(cnsConfig *configuration.CNSConfig) (http.Handler, error) {
 cfg, err := ctrl.GetConfig()
 if err != nil {
-panic(fmt.Errorf("unable to get config: %w", err))
+return nil, errors.Wrap(err, "unable to get a kubeconfig")
 }
 cli, err := client.New(cfg, client.Options{
 Scheme: scheme,
 })
 if err != nil {
-panic(fmt.Errorf("unable to create client: %w", err))
+return nil, errors.Wrap(err, "unable to create a client")
 }
 
 checks := make(map[string]healthz.Checker)
@@ -54,5 +57,5 @@ func NewHealthzHandlerWithChecks(cnsConfig *configuration.CNSConfig) http.Handle
 // otherwise it will look for a check named "healthz" and return a 404 if not there.
 return http.StripPrefix("/healthz", &healthz.Handler{
 Checks: checks,
-})
+}), nil
 }

cns/healthserver/healthz_test.go

@@ -197,7 +197,9 @@ func TestNewHealthzHandlerWithChecks(t *testing.T) {
 configureLocalAPIServer(t, tt.apiStatusCode)
 
 responseRecorder := httptest.NewRecorder()
-healthHandler := NewHealthzHandlerWithChecks(tt.cnsConfig)
+healthHandler, err := NewHealthzHandlerWithChecks(tt.cnsConfig)
+require.NoError(t, err)
+
 healthHandler.ServeHTTP(responseRecorder, httptest.NewRequest("GET", "/healthz", nil))
 
 require.Equal(t, tt.expectedHealthy, responseRecorder.Code == http.StatusOK)

cns/service/main.go

@@ -643,7 +643,11 @@ func main() {
 }),
 }
 
-healthzHandler := healthserver.NewHealthzHandlerWithChecks(cnsconfig)
+healthzHandler, err := healthserver.NewHealthzHandlerWithChecks(cnsconfig)
+if err != nil {
+logger.Errorf("unable to initialize a healthz handler: %v", err)
+return
+}
 go healthserver.Start(z, cnsconfig.MetricsBindAddress, healthzHandler, readyChecker)
 
 nmaConfig, err := nmagent.NewConfig(cnsconfig.WireserverIP)