Add a GCS mirror to WORKSPACE URLs. //hack:update-mirror updates it.

This will help avoid flakes when initializing WORKSPACE, since there are
two sources for each file. Any errors downloading or failed hashes cause
bazel to try the next url in the series.

build/root/WORKSPACE

@@ -1,21 +1,23 @@
+load("//build:workspace_mirror.bzl", "mirror")
+
 http_archive(
     name = "io_bazel_rules_go",
     sha256 = "4b2c61795ac2eefcb28f3eb8e1cb2d8fb3c2eafa0f6712473bc5f93728f38758",
-    urls = ["https://github.com/bazelbuild/rules_go/releases/download/0.10.2/rules_go-0.10.2.tar.gz"],
+    urls = mirror("https://github.com/bazelbuild/rules_go/releases/download/0.10.2/rules_go-0.10.2.tar.gz"),
 )
 
 http_archive(
     name = "io_kubernetes_build",
     sha256 = "007774f06536059f3f782d1a092bddc625d88c17f20bbe731cea844a52485b11",
     strip_prefix = "repo-infra-97099dccc8807e9159dc28f374a8f0602cab07e1",
-    urls = ["https://github.com/kubernetes/repo-infra/archive/97099dccc8807e9159dc28f374a8f0602cab07e1.tar.gz"],
+    urls = mirror("https://github.com/kubernetes/repo-infra/archive/97099dccc8807e9159dc28f374a8f0602cab07e1.tar.gz"),
 )
 
 http_archive(
     name = "bazel_skylib",
     sha256 = "bbccf674aa441c266df9894182d80de104cabd19be98be002f6d478aaa31574d",
     strip_prefix = "bazel-skylib-2169ae1c374aab4a09aa90e65efe1a3aad4e279b",
-    urls = ["https://github.com/bazelbuild/bazel-skylib/archive/2169ae1c374aab4a09aa90e65efe1a3aad4e279b.tar.gz"],
+    urls = mirror("https://github.com/bazelbuild/bazel-skylib/archive/2169ae1c374aab4a09aa90e65efe1a3aad4e279b.tar.gz"),
 )
 
 ETCD_VERSION = "3.2.18"
@@ -25,14 +27,14 @@ new_http_archive(
     build_file = "third_party/etcd.BUILD",
     sha256 = "b729db0732448064271ea6fdcb901773c4fe917763ca07776f22d0e5e0bd4097",
     strip_prefix = "etcd-v%s-linux-amd64" % ETCD_VERSION,
-    urls = ["https://github.com/coreos/etcd/releases/download/v%s/etcd-v%s-linux-amd64.tar.gz" % (ETCD_VERSION, ETCD_VERSION)],
+    urls = mirror("https://github.com/coreos/etcd/releases/download/v%s/etcd-v%s-linux-amd64.tar.gz" % (ETCD_VERSION, ETCD_VERSION)),
 )
 
 http_archive(
     name = "io_bazel_rules_docker",
     sha256 = "c440717ee9b1b2f4a1e9bf5622539feb5aef9db83fc1fa1517818f13c041b0be",
     strip_prefix = "rules_docker-8bbe2a8abd382641e65ff7127a3700a8530f02ce",
-    urls = ["https://github.com/bazelbuild/rules_docker/archive/8bbe2a8abd382641e65ff7127a3700a8530f02ce.tar.gz"],
+    urls = mirror("https://github.com/bazelbuild/rules_docker/archive/8bbe2a8abd382641e65ff7127a3700a8530f02ce.tar.gz"),
 )
 
 load("@bazel_skylib//:lib.bzl", "versions")
@@ -53,7 +55,7 @@ docker_repositories()
 http_file(
     name = "kubernetes_cni",
     sha256 = "f04339a21b8edf76d415e7f17b620e63b8f37a76b2f706671587ab6464411f2d",
-    url = "https://storage.googleapis.com/kubernetes-release/network-plugins/cni-plugins-amd64-v0.6.0.tgz",
+    urls = mirror("https://storage.googleapis.com/kubernetes-release/network-plugins/cni-plugins-amd64-v0.6.0.tgz"),
 )
 
 docker_pull(
@@ -79,3 +81,6 @@ docker_pull(
     repository = "library/busybox",
     tag = "latest",  # ignored, but kept here for documentation
 )
+
+load("//build:workspace_mirror.bzl", "export_urls")
+export_urls("workspace_urls")

build/workspace_mirror.bzl

@@ -0,0 +1,53 @@
+# 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.
+
+prefix = "https://storage.googleapis.com/k8s-bazel-cache/"
+
+def mirror(url):
+  """Try downloading a URL from a GCS mirror first, then from the original.
+
+  Update the GCS bucket using bazel run //hack:update-mirror"""
+  return [prefix + url, url]
+
+# This function only gives proper results when executed from WORKSPACE,
+# but the data is needed in sh_binary, which can only be in a BUILD file.
+# Thus, it is be exported by a repository_rule (which executes in WORKSPACE)
+# to be used by the sh_binary.
+def mirror_urls():
+  urls = []
+  for k, v in native.existing_rules().items():
+    us = list(v.get('urls', []))
+    if 'url' in v:
+      us.append(v['url'])
+    for u in us:
+      if u and not u.startswith(prefix):
+        urls.append(u)
+  return sorted(urls)
+
+def export_urls_impl(repo_ctx):
+  repo_ctx.file(repo_ctx.path("BUILD.bazel"), """
+exports_files(glob(["**"]), visibility=["//visibility:public"])
+""")
+  repo_ctx.file(repo_ctx.path("urls.txt"), content="\n".join(repo_ctx.attr.urls))
+
+_export_urls = repository_rule(
+    attrs = {
+        "urls": attr.string_list(mandatory = True),
+    },
+    local = True,
+    implementation = export_urls_impl,
+)
+
+def export_urls(name):
+  return _export_urls(name=name, urls=mirror_urls())

hack/BUILD

@@ -72,3 +72,10 @@ go_library(
     srcs = ["e2e.go"],
     importpath = "k8s.io/kubernetes/hack",
 )
+
+sh_binary(
+    name = "update-mirror",
+    srcs = ["update-workspace-mirror.sh"],
+    args = ["$(location @workspace_urls//:urls.txt)"],
+    data = ["@workspace_urls//:urls.txt"],
+)

hack/update-workspace-mirror.sh

@@ -0,0 +1,43 @@
+#!/bin/bash
+
+# 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.
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+if [[ $# -ne 1 ]]; then
+    echo 'use "bazel run //build:update-mirror"'
+    echo "(usage: $0 <file with list of URLs to mirror>)"
+    exit 1
+fi
+
+BUCKET="gs://k8s-bazel-cache"
+
+gsutil acl get "${BUCKET}" > /dev/null
+
+tmpfile=$(mktemp bazel_workspace_mirror.XXXXXX)
+trap "rm ${tmpfile}" EXIT
+cat "$1" | while read url; do
+  echo "${url}"
+  if gsutil ls "${BUCKET}/${url}" &> /dev/null; then
+    echo present
+  else
+    echo missing
+    if curl -fLag "${url}" > "${tmpfile}"; then
+        gsutil cp -a public-read "${tmpfile}" "${BUCKET}/${url}"
+    fi
+  fi
+done