Use multiple loadbalancers on GCP

internal/iproute/route.go

@@ -0,0 +1,44 @@
+package iproute
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os/exec"
+	"strings"
+)
+
+// AddToLocalRoutingTable adds the IP to the local routing table.
+func AddToLocalRoutingTable(ctx context.Context, ip string) error {
+	return manipulateLocalRoutingTable(ctx, "add", ip)
+}
+
+// RemoveFromLocalRoutingTable removes the IPfrom the local routing table.
+func RemoveFromLocalRoutingTable(ctx context.Context, ip string) error {
+	return manipulateLocalRoutingTable(ctx, "del", ip)
+}
+
+func manipulateLocalRoutingTable(ctx context.Context, action string, ip string) error {
+	// https://github.com/GoogleCloudPlatform/guest-agent/blob/792fce795218633bcbde505fb3457a0b24f26d37/google_guest_agent/addresses.go#L179
+	if !strings.Contains(ip, "/") {
+		ip = ip + "/32"
+	}
+
+	args := []string{"route", action, "to", "local", ip, "scope", "host", "dev", "ens3", "proto", "66"}
+	_, err := exec.CommandContext(ctx, "ip", args...).Output()
+	if err == nil {
+		return nil
+	}
+	var exitErr *exec.ExitError
+	if !errors.As(err, &exitErr) {
+		return fmt.Errorf("ip route %s: %w", action, err)
+	}
+	if exitErr.ExitCode() == 2 {
+		// "RTNETLINK answers: File exists" or "RTNETLINK answers: No such process"
+		//
+		// Ignore, expected in case of adding an existing route or deleting a route
+		// that does not exist.
+		return nil
+	}
+	return fmt.Errorf("ip route %s (code %v) with: %s", action, exitErr.ExitCode(), exitErr.Stderr)
+}