make dataplanes dual (internal plus external together)

felix/dataplane/driver.go

@@ -67,6 +67,11 @@ func StartDataplaneDriver(
 		return &inactive.InactiveDataplane{}, nil
 	}
 
+	var primaryDataplaneDriver DataplaneDriver
+	var primaryCmd *exec.Cmd
+	var secondaryDataplaneDriver DataplaneDriver
+	var secondaryCmd *exec.Cmd
+
 	if configParams.UseInternalDataplaneDriver {
 		log.Info("Using internal (linux) dataplane driver.")
 		// If kube ipvs interface is present, enable ipvs support.  In BPF mode, we bypass kube-proxy so IPVS
@@ -414,13 +419,30 @@ func StartDataplaneDriver(
 			go aws.WaitForEC2SrcDstCheckUpdate(check, healthAggregator, updater, c)
 		}
 
-		return intDP, nil
-	} else {
+		primaryDataplaneDriver = intDP
+		primaryCmd = nil
+	}
+
+	if configParams.DataplaneDriver != "" {
 		log.WithField("driver", configParams.DataplaneDriver).Info(
 			"Using external dataplane driver.")
 
-		return extdataplane.StartExtDataplaneDriver(configParams.DataplaneDriver)
+		secondaryDataplaneDriver, secondaryCmd = extdataplane.StartExtDataplaneDriver(configParams.DataplaneDriver)
+	}
+
+	if primaryDataplaneDriver != nil && secondaryDataplaneDriver == nil {
+		return primaryDataplaneDriver, primaryCmd
 	}
+
+	if primaryDataplaneDriver == nil && secondaryDataplaneDriver != nil {
+		return secondaryDataplaneDriver, secondaryCmd
+	}
+
+	if primaryDataplaneDriver != nil && secondaryDataplaneDriver != nil {
+		return dataplaneDriverMultiplexer{primaryDriver: primaryDataplaneDriver, secondaryDriver: secondaryDataplaneDriver}, secondaryCmd
+	}
+
+	return nil, nil
 }
 
 func SupportsBPF() error {

felix/dataplane/multiplexer.go

@@ -0,0 +1,38 @@
+// Copyright (c) 2025 NeuReality Ltd.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package dataplane
+
+import "fmt"
+
+type dataplaneDriverMultiplexer struct {
+	primaryDriver   DataplaneDriver
+	secondaryDriver DataplaneDriver
+}
+
+func (multiplexer dataplaneDriverMultiplexer) SendMessage(msg interface{}) error {
+	secondaryErr := multiplexer.secondaryDriver.SendMessage(msg)
+	primaryErr := multiplexer.primaryDriver.SendMessage(msg)
+
+	if primaryErr != nil || secondaryErr != nil {
+		fmt.Errorf("errors in sending message to drivers: primary driver error %w, secondary driver error %w",
+			primaryErr, secondaryErr)
+	}
+
+	return nil
+}
+
+func (multiplexer dataplaneDriverMultiplexer) RecvMessage() (msg interface{}, err error) {
+	return multiplexer.primaryDriver.RecvMessage() // receive message from the primary driver only
+}