Improve etcd-version-monitor metrics proxying, add etcd 3.1 gprc metric support

cluster/images/etcd-version-monitor/BUILD

@@ -19,6 +19,8 @@ go_library(
     deps = [
         "//vendor/github.com/golang/glog:go_default_library",
         "//vendor/github.com/prometheus/client_golang/prometheus:go_default_library",
+        "//vendor/github.com/prometheus/client_golang/prometheus/promhttp:go_default_library",
+        "//vendor/github.com/prometheus/client_model/go:go_default_library",
         "//vendor/github.com/prometheus/common/expfmt:go_default_library",
         "//vendor/github.com/spf13/pflag:go_default_library",
     ],

cluster/images/etcd-version-monitor/Makefile

@@ -20,7 +20,7 @@
 ARCH:=amd64
 GOLANG_VERSION?=1.8.3
 REGISTRY?=gcr.io/google-containers
-TAG?=0.1.0
+TAG?=0.1.1
 IMAGE:=$(REGISTRY)/etcd-version-monitor:$(TAG)
 CURRENT_DIR:=$(pwd)
 TEMP_DIR:=$(shell mktemp -d)

cluster/images/etcd-version-monitor/README.md

 # etcd-version-monitor
 
-This is a tool for exporting metrics related to etcd version, like etcd
-server's binary version, cluster version, and counts of different kinds of
-gRPC calls (which is a characteristic of v3), etc. These metrics are in
+This is a tool for exporting etcd metrics and supplementing them with etcd
+server binary version and cluster version. These metrics are in
 prometheus format and can be scraped by a prometheus server.
 The metrics are exposed at the http://localhost:9101/metrics endpoint.
 
+For etcd 3.1+, the
+[go-grpc-prometheus](https://github.com/grpc-ecosystem/go-grpc-prometheus)
+metrics format, which backward incompatibly replaces the 3.0 legacy grpc metric
+format, is exposed in both the 3.1 format and in the 3.0. This preserves
+backward compatiblity.
+
+For etcd 3.1+, the `--metrics=extensive` must be set on etcd for grpc request
+latency metrics (`etcd_grpc_unary_requests_duration_seconds`) to be exposed.
+
 **RUNNING THE TOOL**
 
 To run this tool as a docker container: