Add flags to customize listen ports and detect port collisions

controllers/nginx/pkg/cmd/controller/utils.go

@@ -17,7 +17,9 @@ limitations under the License.
 package main
 
 import (
+	"fmt"
 	"io/ioutil"
+	"net"
 	"os"
 	"os/exec"
 	"syscall"
@@ -74,3 +76,12 @@ func diff(b1, b2 []byte) ([]byte, error) {
 	out, _ := exec.Command("diff", "-u", f1.Name(), f2.Name()).CombinedOutput()
 	return out, nil
 }
+
+func isPortAvailable(p int) bool {
+	ln, err := net.Listen("tcp", fmt.Sprintf(":%v", p))
+	if err != nil {
+		return false
+	}
+	ln.Close()
+	return true
+}