[admin_api] minor things

admin/admin.go

@@ -18,6 +18,9 @@
 
 // Package admin implements the admin service. It is a convenient API to expose
 // states in the gRPC library.
+//
+// Notice: This package is EXPERIMENTAL and may be changed or removed in a later
+// release.
 package admin
 
 import (
@@ -41,7 +44,7 @@ func init() {
 // allocated for the service handlers.
 //
 // Note that if the server is not a *grpc.Server or a *xds.GRPCServer, CSDS will
-// not be registered due to CSDS generated code is too old and doesn't support
+// not be registered because CSDS generated code is old and doesn't support
 // interface `grpc.ServiceRegistrar`.
 // https://github.com/envoyproxy/go-control-plane/issues/403
 func Register(s grpc.ServiceRegistrar) (cleanup func(), _ error) {

xds/xds.go

@@ -52,11 +52,15 @@ func init() {
 		case *GRPCServer:
 			sss, ok := ss.gs.(*grpc.Server)
 			if !ok {
-				return nil, fmt.Errorf("grpc server within xds.GRPCServer is not *grpc.Server, CSDS will not be registered")
+				logger.Warningf("grpc server within xds.GRPCServer is not *grpc.Server, CSDS will not be registered")
+				return nil, nil
 			}
 			grpcServer = sss
 		default:
-			return nil, fmt.Errorf("server to register service on is neither a *grpc.Server or a *xds.GRPCServer, CSDS will not be registered")
+			// Returning an error would cause the top level admin.Register() to
+			// fail. Log a warning instead.
+			logger.Warningf("server to register service on is neither a *grpc.Server or a *xds.GRPCServer, CSDS will not be registered")
+			return nil, nil
 		}
 
 		csdss, err := csds.NewClientStatusDiscoveryServer()