Adding a shutdown script that would enable handling preemptible VM terminations gracefully in GCP environment

Signed-off-by: Vishnu kannan <vishnuk@google.com>

cluster/gce/gci/BUILD

@@ -28,6 +28,7 @@ release_filegroup(
         "configure.sh",
         "master.yaml",
         "node.yaml",
+        "shutdown.sh",
     ],
     visibility = ["//visibility:public"],
 )

cluster/gce/gci/node-helper.sh

@@ -28,6 +28,7 @@ function get-node-instance-metadata {
   metadata+="gci-update-strategy=${KUBE_TEMP}/gci-update.txt,"
   metadata+="gci-ensure-gke-docker=${KUBE_TEMP}/gci-ensure-gke-docker.txt,"
   metadata+="gci-docker-version=${KUBE_TEMP}/gci-docker-version.txt,"
+  metadata+="shutdown-script=${KUBE_ROOT}/cluster/gce/gci/shutdown.sh,"
   metadata+="${NODE_EXTRA_METADATA}"
   echo "${metadata}"
 }

cluster/gce/gci/shutdown.sh

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+
+# Copyright 2016 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.
+
+# A script that let's gci preemptible nodes gracefully terminate in the event of a VM shutdown.
+preemptible=$(curl "http://metadata.google.internal/computeMetadata/v1/instance/scheduling/preemptible" -H "Metadata-Flavor: Google")
+if [ ${preemptible} == "TRUE" ]; then
+    echo "Shutting down! Sleeping for a minute to let the node gracefully terminate"
+    # https://cloud.google.com/compute/docs/instances/stopping-or-deleting-an-instance#delete_timeout
+    sleep 30
+fi