Build images from tar archives

This patch introduces TarBits, an implementation of Bits for building
the node image from Kubernetes tar image archives.

The -type is "tar" and -kube-root may be set to one of three values:

  1. A local filesystem path containing the files listed above in a flat
     structure. To prevent an existing local

  2. An HTTP address that contains the files listed above in a structure
     that adheres to the layout of the public GCS buckets kubernetes-release
     and kubernetes-release-dev. For example, if tarRoot is set to
     https://k8s.ci/v1.13 then the following URIs should be valid:

       * https://k8s.ci/v1.13/kubernetes.tar.gz
       * https://k8s.ci/v1.13/bin/GOOS/GOARCH/kube-apiserver.tar
       * https://k8s.ci/v1.13/bin/GOOS/GOARCH/kube-controller-manager.tar
       * https://k8s.ci/v1.13/bin/GOOS/GOARCH/kube-scheduler.tar
       * https://k8s.ci/v1.13/bin/GOOS/GOARCH/kube-proxy.tar
       * https://k8s.ci/v1.13/bin/GOOS/GOARCH/kubeadm
       * https://k8s.ci/v1.13/bin/GOOS/GOARCH/kubectl
       * https://k8s.ci/v1.13/bin/GOOS/GOARCH/kubelet

     The files are downloaded to "$HOME/.kind/tarbits/VERSION" where
     VERSION is the value of the "version" file extracted from the
     kubernetes tarball.

  3. A valid semantic version for a released version of Kubernetes or
     begins with "ci/" or "release/". If the string matches any of these
     then the value is presumed to be a CI or release build hosted on one
     of the public GCS buckets.

     This option also supports values ended with ".txt", ex. "ci/latest.txt".
     In fact, all values beginning with "ci/" or "release/" are first checked
     to see if there's a matching txt file for that value. For example,
     if "ci/latest" is provided then before assuming that is a directory,
     "ci/latest.txt" is queried.

In order to prevent the second two options from conflicting with the first,
a local file path, using the prefix "file://" explicitly indicates the given
tarRoot is a local file path.

The given tarRoot may also take the format tarRoot::localPath where the
tarRoot is separated from the local path where the remote files will be
downloaded.

If no explicit local path is provided then remote files are downloaded to
"$HOME/.kind/tarbits/VERSION" where VERSION is the value extracted from
the "version" file in the "kubernetes.tar.gz" tarball.

If a file is already present on disk with the same size as the remote
equivalent, the file will not be downloaded again.

cmd/kind/build/nodeimage/nodeimage.go

@@ -46,7 +46,7 @@ func NewCommand() *cobra.Command {
 	}
 	cmd.Flags().StringVar(
 		&flags.BuildType, "type",
-		"docker", "build type, one of [bazel, docker, apt]",
+		"docker", "build type, one of [bazel, docker, apt, tar]",
 	)
 	cmd.Flags().StringVar(
 		&flags.Image, "image",

pkg/build/kube/files.go

@@ -0,0 +1,44 @@
+/*
+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 kube
+
+const kubeletService = `[Unit]
+Description=kubelet: The Kubernetes Node Agent
+Documentation=http://kubernetes.io/docs/
+
+[Service]
+ExecStart=/usr/bin/kubelet
+Restart=always
+StartLimitInterval=0
+RestartSec=10
+
+[Install]
+WantedBy=multi-user.target
+`
+
+const tenKubeadmConf = `# Note: This dropin only works with kubeadm and kubelet v1.11+
+[Service]
+Environment="KUBELET_KUBECONFIG_ARGS=--bootstrap-kubeconfig=/etc/kubernetes/bootstrap-kubelet.conf --kubeconfig=/etc/kubernetes/kubelet.conf"
+Environment="KUBELET_CONFIG_ARGS=--config=/var/lib/kubelet/config.yaml"
+# This is a file that "kubeadm init" and "kubeadm join" generates at runtime, populating the KUBELET_KUBEADM_ARGS variable dynamically
+EnvironmentFile=-/var/lib/kubelet/kubeadm-flags.env
+# This is a file that the user can use for overrides of the kubelet args as a last resort. Preferably, the user should use
+# the .NodeRegistration.KubeletExtraArgs object in the configuration files instead. KUBELET_EXTRA_ARGS should be sourced from this file.
+EnvironmentFile=-/etc/default/kubelet
+ExecStart=
+ExecStart=/usr/bin/kubelet $KUBELET_KUBECONFIG_ARGS $KUBELET_CONFIG_ARGS $KUBELET_KUBEADM_ARGS $KUBELET_EXTRA_ARGS
+`