Kubeadm-initialised kubelet uses provided hostname if present

If --node-name is passed in to `kubeadm init`, `--hostname-override` will be
passed to kubelet.

cmd/kubeadm/app/phases/kubelet/flags.go

@@ -28,6 +28,7 @@ import (
 	kubeadmapiv1alpha2 "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/v1alpha2"
 	"k8s.io/kubernetes/cmd/kubeadm/app/constants"
 	kubeadmutil "k8s.io/kubernetes/cmd/kubeadm/app/util"
+	nodeutil "k8s.io/kubernetes/pkg/util/node"
 	"k8s.io/kubernetes/pkg/util/procfs"
 	utilsexec "k8s.io/utils/exec"
 )
@@ -78,7 +79,12 @@ func buildKubeletArgMap(nodeRegOpts *kubeadmapi.NodeRegistrationOptions, registe
 		kubeletFlags["resolv-conf"] = "/run/systemd/resolve/resolv.conf"
 	}
 
-	// TODO: Pass through --hostname-override if a custom name is used?
+	// Make sure the node name we're passed will work with Kubelet
+	if nodeRegOpts.Name != "" && nodeRegOpts.Name != nodeutil.GetHostname("") {
+		glog.V(1).Info("setting kubelet hostname-override to %q", nodeRegOpts.Name)
+		kubeletFlags["hostname-override"] = nodeRegOpts.Name
+	}
+
 	// TODO: Conditionally set `--cgroup-driver` to either `systemd` or `cgroupfs` for CRI other than Docker
 
 	return kubeletFlags

cmd/kubeadm/app/phases/kubelet/flags_test.go

@@ -0,0 +1,62 @@
+/*
+Copyright 2018 The Kubernetes 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 kubelet
+
+import (
+	"testing"
+
+	kubeadmapi "k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm"
+	nodeutil "k8s.io/kubernetes/pkg/util/node"
+)
+
+func TestBuildKubeletArgMap(t *testing.T) {
+
+	tests := []struct {
+		name             string
+		hostname         string
+		expectedHostname string
+	}{
+		{
+			name:             "manually set to current hostname",
+			hostname:         nodeutil.GetHostname(""),
+			expectedHostname: "",
+		},
+		{
+			name:             "unset hostname",
+			hostname:         "",
+			expectedHostname: "",
+		},
+		{
+			name:             "override hostname",
+			hostname:         "my-node",
+			expectedHostname: "my-node",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			opts := &kubeadmapi.NodeRegistrationOptions{
+				Name: test.hostname,
+			}
+
+			m := buildKubeletArgMap(opts, false)
+			if m["hostname-override"] != test.expectedHostname {
+				t.Errorf("expected hostname %q, got %q", test.expectedHostname, m["hostname-override"])
+			}
+		})
+	}
+}