kubeadm: Warn on API server bind address override

ChooseAPIServerBindAddress is silently overriding the requested bind IP address for the API server if that address is deemed unsuitable. This is currently done only if the IP is a loopback one (127.0.0.0/8; ::1/128). It's best to at least issue a warning if such override occurs, so that there are no surprised users by this. Signed-off-by: Rostislav M. Georgiev <rostislavg@vmware.com>

kubeadm: Warn on API server bind address override
b46fbbc4 · Rostislav M. Georgiev · 973b5d29 · b46fbbc4
Commit b46fbbc4 authored Nov 16, 2018 by Rostislav M. Georgiev
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common.go cmd/kubeadm/app/util/config/common.go +4 -0

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--- a/cmd/kubeadm/app/util/config/common.go
+++ b/cmd/kubeadm/app/util/config/common.go
@@ -19,6 +19,7 @@ package config
 import (
 	"io/ioutil"
 	"net"
+	"reflect"
 	"strings"

 	"github.com/pkg/errors"
@@ -175,5 +176,8 @@ func ChooseAPIServerBindAddress(bindAddress net.IP) (net.IP, error) {
 		}
 		return nil, err
 	}
+	if bindAddress != nil && !bindAddress.IsUnspecified() && !reflect.DeepEqual(ip, bindAddress) {
+		klog.Warningf("WARNING: overriding requested API server bind address: requested %q, actual %q", bindAddress, ip)
+	}
 	return ip, nil
 }