receiver: implemented Prometheus receiver

This Prometheus receiver requires adding yaml
definitions to the configuration file under "receivers"

```yaml
receivers:
   prometheus:
     - job_name: 'ocjdbc'
        scrape_interval: 5s
        static_configs:
          - targets: ['localhost:9988']

     - job_name: 'kafka_metrics'
         scrape_interval: 4s
         static_configs:
           - targets: ['localhost:8887']

     buffer_period: 500ms
     buffer_count: 2
```

Also added and end-to-end test to ensure that a full scrape by the
receiver produces tangible metrics that are then consumed
by the agent or whatever metrics sinks exist.

Fixes #137

Author: odeke-em

README.md

@@ -130,6 +130,14 @@ receivers:
   jaeger:
     jaeger-thrift-tchannel-port: 14267
     jaeger-thrift-http-port: 14268
+
+  prometheus:
+    config:
+      scrape_configs:
+        - job_name: 'caching_cluster'
+          scrape_interval: 5s
+          static_configs:
+            - targets: ['localhost:8889']
 ```
 
 ### <a name="config-exporters"></a>Exporters

cmd/ocagent/main.go

@@ -38,6 +38,7 @@ import (
 	"github.com/census-instrumentation/opencensus-service/receiver"
 	"github.com/census-instrumentation/opencensus-service/receiver/jaeger"
 	"github.com/census-instrumentation/opencensus-service/receiver/opencensus"
+	promreceiver "github.com/census-instrumentation/opencensus-service/receiver/prometheus"
 	"github.com/census-instrumentation/opencensus-service/receiver/zipkin"
 	"github.com/census-instrumentation/opencensus-service/receiver/zipkin/scribe"
 )
@@ -135,6 +136,15 @@ func runOCAgent() {
 		closeFns = append(closeFns, jaegerDoneFn)
 	}
 
+	// If the Prometheus receiver is enabled, then run it.
+	if agentConfig.PrometheusReceiverEnabled() {
+		promDoneFn, err := runPrometheusReceiver(agentConfig.PrometheusConfiguration(), commonMetricsSink)
+		if err != nil {
+			log.Fatal(err)
+		}
+		closeFns = append(closeFns, promDoneFn)
+	}
+
 	// Always cleanup finally
 	defer func() {
 		for _, closeFn := range closeFns {
@@ -268,3 +278,18 @@ func runZipkinScribeReceiver(config *config.ScribeReceiverConfig, sr receiver.Tr
 	log.Printf("Running Zipkin Scribe receiver with %+v", *config)
 	return doneFn, nil
 }
+
+func runPrometheusReceiver(promConfig *promreceiver.Configuration, mr receiver.MetricsReceiverSink) (doneFn func() error, err error) {
+	pmr, err := promreceiver.New(promConfig)
+	if err != nil {
+		return nil, err
+	}
+	if err := pmr.StartMetricsReception(context.Background(), mr); err != nil {
+		return nil, err
+	}
+	doneFn = func() error {
+		return pmr.StopMetricsReception(context.Background())
+	}
+	log.Print("Running Prometheus receiver")
+	return doneFn, nil
+}

example/main.go

@@ -17,6 +17,7 @@ package main
 
 import (
 	"context"
+	"fmt"
 	"log"
 	"math/rand"
 	"time"
@@ -29,13 +30,17 @@ import (
 )
 
 func main() {
-	oce, err := ocagent.NewExporter(ocagent.WithInsecure())
+	oce, err := ocagent.NewExporter(
+		ocagent.WithInsecure(),
+		ocagent.WithServiceName("example-go"))
 	if err != nil {
 		log.Fatalf("Failed to create ocagent-exporter: %v", err)
 	}
 	trace.RegisterExporter(oce)
 	view.RegisterExporter(oce)
 
+	// Some configurations to get observability signals out.
+	view.SetReportingPeriod(7 * time.Second)
 	trace.ApplyConfig(trace.Config{
 		DefaultSampler: trace.AlwaysSample(),
 	})
@@ -45,12 +50,14 @@ func main() {
 	keyMethod, _ := tag.NewKey("method")
 
 	mLatencyMs := stats.Float64("latency", "The latency in milliseconds", "ms")
+	mLineLengths := stats.Int64("line_lengths", "The length of each line", "By")
+
 	views := []*view.View{
 		{
 			Name:        "opdemo/latency",
-			Description: "The various counts",
+			Description: "The various latencies of the methods",
 			Measure:     mLatencyMs,
-			Aggregation: view.Distribution(0, 10, 50, 100, 200, 400, 800, 1000, 1400, 2000, 5000, 10000),
+			Aggregation: view.Distribution(0, 10, 50, 100, 200, 400, 800, 1000, 1400, 2000, 5000, 10000, 15000),
 			TagKeys:     []tag.Key{keyClient, keyMethod},
 		},
 		{
@@ -60,6 +67,20 @@ func main() {
 			Aggregation: view.Count(),
 			TagKeys:     []tag.Key{keyClient, keyMethod},
 		},
+		{
+			Name:        "opdemo/line_lengths",
+			Description: "The lengths of the various lines in",
+			Measure:     mLineLengths,
+			Aggregation: view.Distribution(0, 10, 20, 50, 100, 150, 200, 500, 800),
+			TagKeys:     []tag.Key{keyClient, keyMethod},
+		},
+		{
+			Name:        "opdemo/line_counts",
+			Description: "The counts of the lines in",
+			Measure:     mLineLengths,
+			Aggregation: view.Count(),
+			TagKeys:     []tag.Key{keyClient, keyMethod},
+		},
 	}
 
 	if err := view.Register(views...); err != nil {
@@ -71,9 +92,31 @@ func main() {
 	for {
 		startTime := time.Now()
 		_, span := trace.StartSpan(context.Background(), "Foo")
-		time.Sleep(time.Duration(rng.Int63n(13000)) * time.Millisecond)
+		var sleep int64
+		switch modulus := time.Now().Unix() % 5; modulus {
+		case 0:
+			sleep = rng.Int63n(17001)
+		case 1:
+			sleep = rng.Int63n(8007)
+		case 2:
+			sleep = rng.Int63n(917)
+		case 3:
+			sleep = rng.Int63n(87)
+		case 4:
+			sleep = rng.Int63n(1173)
+		}
+
+		time.Sleep(time.Duration(sleep) * time.Millisecond)
+
 		span.End()
 		latencyMs := float64(time.Since(startTime)) / 1e6
+		nr := int(rng.Int31n(7))
+		for i := 0; i < nr; i++ {
+			randLineLength := rng.Int63n(999)
+			stats.Record(ctx, mLineLengths.M(randLineLength))
+			fmt.Printf("#%d: LineLength: %dBy\n", i, randLineLength)
+		}
 		stats.Record(ctx, mLatencyMs.M(latencyMs))
+		fmt.Printf("Latency: %.3fms\n", latencyMs)
 	}
 }

go.mod

@@ -4,7 +4,9 @@ require (
 	cloud.google.com/go v0.32.0 // indirect
 	contrib.go.opencensus.io/exporter/ocagent v0.4.3
 	contrib.go.opencensus.io/exporter/stackdriver v0.9.1
-	git.apache.org/thrift.git v0.0.0-20181101003639-92be4f312b88
+	git.apache.org/thrift.git v0.0.0-20181101003639-92be4f312b88 // indirect
+	github.com/Azure/azure-sdk-for-go v6.0.0-beta+incompatible // indirect
+	github.com/Azure/go-autorest v11.4.0+incompatible // indirect
 	github.com/BurntSushi/toml v0.3.1 // indirect
 	github.com/DataDog/datadog-go v0.0.0-20180822151419-281ae9f2d895 // indirect
 	github.com/DataDog/opencensus-go-exporter-datadog v0.0.0-20181026070331-e7c4bd17b329
@@ -13,38 +15,50 @@ require (
 	github.com/aws/aws-sdk-go v1.15.68 // indirect
 	github.com/bmizerany/perks v0.0.0-20141205001514-d9a9656a3a4b // indirect
 	github.com/census-instrumentation/opencensus-proto v0.1.0-0.20181214143942-ba49f56771b8
-	github.com/codahale/hdrhistogram v0.0.0-20161010025455-3a0bb77429bd // indirect
-	github.com/go-kit/kit v0.8.0 // indirect
+	github.com/dgrijalva/jwt-go v3.2.0+incompatible // indirect
+	github.com/go-logfmt/logfmt v0.4.0 // indirect
 	github.com/gogo/googleapis v1.1.0 // indirect
-	github.com/gogo/protobuf v1.1.1 // indirect
+	github.com/golang/groupcache v0.0.0-20190129154638-5b532d6fd5ef // indirect
 	github.com/golang/protobuf v1.2.0
+	github.com/google/gofuzz v0.0.0-20170612174753-24818f796faf // indirect
+	github.com/googleapis/gnostic v0.2.0 // indirect
+	github.com/gophercloud/gophercloud v0.0.0-20190206021053-df38e1611dbe // indirect
 	github.com/gorilla/context v1.1.1 // indirect
 	github.com/gorilla/mux v1.6.2
-	github.com/grpc-ecosystem/grpc-gateway v1.5.0
+	github.com/gregjones/httpcache v0.0.0-20190203031600-7a902570cb17 // indirect
+	github.com/grpc-ecosystem/grpc-gateway v1.6.3
+	github.com/hashicorp/consul v1.4.2 // indirect
+	github.com/hashicorp/go-cleanhttp v0.5.0 // indirect
+	github.com/hashicorp/go-rootcerts v1.0.0 // indirect
+	github.com/hashicorp/serf v0.8.2 // indirect
 	github.com/inconshreveable/mousetrap v1.0.0 // indirect
 	github.com/jaegertracing/jaeger v1.8.2
 	github.com/jmespath/go-jmespath v0.0.0-20180206201540-c2b33e8439af // indirect
-	github.com/kr/pretty v0.1.0 // indirect
+	github.com/json-iterator/go v1.1.5 // indirect
 	github.com/mitchellh/mapstructure v1.1.2 // indirect
+	github.com/modern-go/reflect2 v1.0.1 // indirect
 	github.com/omnition/scribe-go v0.0.0-20190131012523-9e3c68f31124
+	github.com/onsi/ginkgo v1.7.0 // indirect
+	github.com/onsi/gomega v1.4.3 // indirect
 	github.com/opentracing/opentracing-go v1.0.2 // indirect
 	github.com/openzipkin/zipkin-go v0.1.3
 	github.com/orijtech/prometheus-go-metrics-exporter v0.0.2
+	github.com/orijtech/promreceiver v0.0.3
+	github.com/peterbourgon/diskv v2.0.1+incompatible // indirect
 	github.com/philhofer/fwd v1.0.0 // indirect
 	github.com/pkg/errors v0.8.0
-	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/prashantv/protectmem v0.0.0-20171002184600-e20412882b3a // indirect
-	github.com/prometheus/client_golang v0.8.0
-	github.com/prometheus/procfs v0.0.0-20180725123919-05ee40e3a273
+	github.com/prometheus/client_golang v0.9.1
+	github.com/prometheus/procfs v0.0.0-20181005140218-185b4288413d
+	github.com/prometheus/prometheus v0.0.0-20190131111325-62e591f928dd
 	github.com/rs/cors v1.6.0
+	github.com/samuel/go-zookeeper v0.0.0-20180130194729-c4fab1ac1bec // indirect
 	github.com/soheilhy/cmux v0.1.4
 	github.com/spf13/cast v1.2.0
 	github.com/spf13/cobra v0.0.3
-	github.com/spf13/pflag v1.0.3 // indirect
 	github.com/spf13/viper v1.2.1
 	github.com/streadway/quantile v0.0.0-20150917103942-b0c588724d25 // indirect
 	github.com/stretchr/objx v0.1.1 // indirect
-	github.com/stretchr/testify v1.2.2 // indirect
 	github.com/tinylib/msgp v1.0.2 // indirect
 	github.com/uber-go/atomic v1.3.2 // indirect
 	github.com/uber/jaeger-client-go v2.15.0+incompatible // indirect
@@ -55,16 +69,19 @@ require (
 	go.uber.org/atomic v1.3.2 // indirect
 	go.uber.org/multierr v1.1.0 // indirect
 	go.uber.org/zap v1.9.1
-	golang.org/x/lint v0.0.0-20181026193005-c67002cb31c3 // indirect
-	golang.org/x/net v0.0.0-20181102091132-c10e9556a7bc
+	golang.org/x/crypto v0.0.0-20190131182504-b8fe1690c613 // indirect
 	golang.org/x/oauth2 v0.0.0-20181102170140-232e45548389 // indirect
-	golang.org/x/sys v0.0.0-20181031143558-9b800f95dbbc // indirect
-	golang.org/x/text v0.3.0
+	golang.org/x/time v0.0.0-20181108054448-85acf8d2951c // indirect
 	google.golang.org/api v0.0.0-20181102150758-04bb50b6b83d
 	google.golang.org/appengine v1.3.0 // indirect
 	google.golang.org/genproto v0.0.0-20181101192439-c830210a61df // indirect
-	google.golang.org/grpc v1.16.0
+	google.golang.org/grpc v1.17.0
 	gopkg.in/DataDog/dd-trace-go.v1 v1.4.0 // indirect
 	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
+	gopkg.in/fsnotify/fsnotify.v1 v1.4.7 // indirect
+	gopkg.in/inf.v0 v0.9.1 // indirect
 	gopkg.in/yaml.v2 v2.2.1
+	k8s.io/apimachinery v0.0.0-20190207091153-095b9d203467 // indirect
+	k8s.io/kube-openapi v0.0.0-20190205224424-fd29a9f2f429 // indirect
+	sigs.k8s.io/structured-merge-diff v0.0.0-20190130003954-e5e029740eb8 // indirect
 )