feat(gateway): add fib_multipath_hash_policy support for L4-aware ECMP flow distribution

Author: MircoBarone

cmd/gateway/main.go

@@ -118,6 +118,12 @@ func run(cmd *cobra.Command, _ []string) error {
 		return err
 	}
 
+	// Enable Multipath Hash Policy if required.
+	if connoptions.GwOptions.EnableMultipathHashPolicy {
+		if err = kernel.EnableMultipathHashPolicy(); err != nil {
+			return fmt.Errorf("failed to enable multipath hash policy: %w", err)
+		}
+	}
 	// Set controller-runtime logger.
 	log.SetLogger(klog.NewKlogr())
 

pkg/gateway/flags.go

@@ -77,6 +77,8 @@ const (
 	FlagNameDisableKernelVersionCheck FlagName = "disable-kernel-version-check"
 	// FlagNameMinimumKernelVersion is the minimum kernel version required by Liqo.
 	FlagNameMinimumKernelVersion FlagName = "minimum-kernel-version"
+	// FlagNameEnableMultipathHashPolicy sets fib_multipath_hash_policy=1 to enable 5-tuple hashing for multipath routing.
+	FlagNameEnableMultipathHashPolicy FlagName = "enable-multipath-hash-policy"
 )
 
 // RequiredFlags contains the list of the mandatory flags.
@@ -125,6 +127,8 @@ func InitFlags(flagset *pflag.FlagSet, opts *Options) {
 
 	flagset.BoolVar(&opts.DisableKernelVersionCheck, FlagNameDisableKernelVersionCheck.String(), false, "Disable the kernel version check")
 	flagset.Var(&opts.MinimumKernelVersion, FlagNameMinimumKernelVersion.String(), "Minimum kernel version required by Liqo")
+	flagset.BoolVar(&opts.EnableMultipathHashPolicy, FlagNameEnableMultipathHashPolicy.String(), false,
+		"Set fib_multipath_hash_policy=1 to use 5-tuple hashing for multipath routing")
 }
 
 // MarkFlagsRequired marks the flags as required.

pkg/gateway/options.go

@@ -51,6 +51,7 @@ type Options struct {
 
 	DisableKernelVersionCheck bool
 	MinimumKernelVersion      kernelversion.KernelVersion
+	EnableMultipathHashPolicy bool
 }
 
 // NewOptions returns a new Options struct.

pkg/utils/kernel/multipathpolicy.go

@@ -0,0 +1,36 @@
+// Copyright 2019-2026 The Liqo Authors
+//
+// 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 kernel
+
+import (
+	"fmt"
+	"os"
+)
+
+const multipathpolicyFile = "/proc/sys/net/ipv4/fib_multipath_hash_policy"
+
+// EnableMultipathHashPolicy enables 5-tuple hashing for multipath routing by writing 1 to /proc/sys/net/ipv4/fib_multipath_hash_policy.
+func EnableMultipathHashPolicy() error {
+	file, err := os.OpenFile(multipathpolicyFile, os.O_WRONLY, 0o600)
+	if err != nil {
+		return fmt.Errorf("failed to open multipath policy file %s: %w", multipathpolicyFile, err)
+	}
+	defer file.Close()
+
+	if _, err := file.WriteString("1\n"); err != nil {
+		return fmt.Errorf("failed to write to multipath policy file %s: %w", multipathpolicyFile, err)
+	}
+	return nil
+}