envtest: export DefaultKubeAPIServerFlags & make it configurable

This change exports DefaultKubeAPIServerFlags, allowing a user to
append the default flags with other custom flags and set it to
Environment.KubeAPIServerFlags.
If KubeAPIServerFlags is not set, DefaultKubeAPIServerFlags is used when
the API server starts.

pkg/envtest/server.go

@@ -46,9 +46,8 @@ func defaultAssetPath(binary string) string {
 
 }
 
-// APIServerDefaultArgs are flags necessary to bring up apiserver.
-// TODO: create test framework interface to append flag to default flags.
-var defaultKubeAPIServerFlags = []string{
+// DefaultKubeAPIServerFlags are default flags necessary to bring up apiserver.
+var DefaultKubeAPIServerFlags = []string{
 	"--etcd-servers={{ if .EtcdURL }}{{ .EtcdURL.String }}{{ end }}",
 	"--cert-dir={{ .CertDir }}",
 	"--insecure-port={{ if .URL }}{{ .URL.Port }}{{ end }}",
@@ -76,6 +75,9 @@ type Environment struct {
 	// existing kubeconfig, instead of trying to stand up a new control plane.
 	// This is useful in cases that need aggregated API servers and the like.
 	UseExistingCluster bool
+
+	// KubeAPIServerFlags is the set of flags passed while starting the api server.
+	KubeAPIServerFlags []string
 }
 
 // Stop stops a running server
@@ -88,6 +90,11 @@ func (te *Environment) Stop() error {
 
 // Start starts a local Kubernetes server and updates te.ApiserverPort with the port it is listening on
 func (te *Environment) Start() (*rest.Config, error) {
+	// Set default API server flags if not set.
+	if len(te.KubeAPIServerFlags) == 0 {
+		te.KubeAPIServerFlags = DefaultKubeAPIServerFlags
+	}
+
 	if te.UseExistingCluster {
 		if te.Config == nil {
 			// we want to allow people to pass in their own config, so
@@ -101,7 +108,7 @@ func (te *Environment) Start() (*rest.Config, error) {
 		}
 	} else {
 		te.ControlPlane = integration.ControlPlane{}
-		te.ControlPlane.APIServer = &integration.APIServer{Args: defaultKubeAPIServerFlags}
+		te.ControlPlane.APIServer = &integration.APIServer{Args: te.KubeAPIServerFlags}
 		if os.Getenv(envKubeAPIServerBin) == "" {
 			te.ControlPlane.APIServer.Path = defaultAssetPath("kube-apiserver")
 		}