Add option to map measurement names to field name into prometheus input

plugins/inputs/prometheus/README.md

@@ -17,6 +17,8 @@ in Prometheus format.
   ## Use bearer token for authorization
   # bearer_token = /path/to/bearer/token
 
+  # measurement_name_as_field_name = true
+
   ## Specify timeout duration for slower prometheus clients (default is 3s)
   # response_timeout = "3s"
 
@@ -43,6 +45,25 @@ If set, the file specified by the `bearer_token` parameter will be read on
 each interval and its contents will be appended to the Bearer string in the
 Authorization header.
 
+
+### Measurement Name as Field Name
+
+If `measurement_name_as_field_name` set, output metric fields will use measurement as name instead of `gauge`,
+`counter` etc. This is useful for example in the case when you want to map all 
+metrics under single measurement using `name_override` and still be able to separate
+metrics.
+
+#### Example of output using `measurement_name_as_field_name`
+**Source**
+```
+cpu_usage_user{cpu="cpu3"} 1.5045135406226022
+```
+**Output**
+```
+cpu_usage_user,cpu=cpu3,url=http://example.org:9273/metrics cpu_usage_user=1.5228426395944945 1505776751000000000
+```
+
+
 ### Usage for Caddy HTTP server
 
 If you want to monitor Caddy, you need to use Caddy with its Prometheus plugin:

plugins/inputs/prometheus/prometheus.go

@@ -25,6 +25,9 @@ type Prometheus struct {
 	// An array of Kubernetes services to scrape metrics from.
 	KubernetesServices []string
 
+	// Use measurment name as field name instead of gauge, counter etc.
+	MeasurementNameAsFieldName bool `toml:"measurement_name_as_field_name"`
+
 	// Bearer Token authorization file path
 	BearerToken string `toml:"bearer_token"`
 
@@ -218,18 +221,26 @@ func (p *Prometheus) gatherURL(url UrlAndAddress, acc telegraf.Accumulator) erro
 		if url.Address != "" {
 			tags["address"] = url.Address
 		}
-
+		fields := metric.Fields()
+		if p.MeasurementNameAsFieldName {
+			newFields := make(map[string]interface{})
+			for _, v := range fields {
+				newFields[metric.Name()] = v
+				break // fields should only contain one metric as per spec
+			}
+			fields = newFields
+		}
 		switch metric.Type() {
 		case telegraf.Counter:
-			acc.AddCounter(metric.Name(), metric.Fields(), tags, metric.Time())
+			acc.AddCounter(metric.Name(), fields, tags, metric.Time())
 		case telegraf.Gauge:
-			acc.AddGauge(metric.Name(), metric.Fields(), tags, metric.Time())
+			acc.AddGauge(metric.Name(), fields, tags, metric.Time())
 		case telegraf.Summary:
-			acc.AddSummary(metric.Name(), metric.Fields(), tags, metric.Time())
+			acc.AddSummary(metric.Name(), fields, tags, metric.Time())
 		case telegraf.Histogram:
-			acc.AddHistogram(metric.Name(), metric.Fields(), tags, metric.Time())
+			acc.AddHistogram(metric.Name(), fields, tags, metric.Time())
 		default:
-			acc.AddFields(metric.Name(), metric.Fields(), tags, metric.Time())
+			acc.AddFields(metric.Name(), fields, tags, metric.Time())
 		}
 	}
 

plugins/inputs/prometheus/prometheus_test.go

@@ -78,6 +78,32 @@ func TestPrometheusGeneratesMetricsWithHostNameTag(t *testing.T) {
 	assert.True(t, acc.TagValue("test_metric", "url") == ts.URL)
 }
 
+func TestPrometheusGeneratesMetricsWithHostNameTagAndMeasurementNameAsFieldName(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintln(w, sampleTextFormat)
+	}))
+	defer ts.Close()
+
+	p := &Prometheus{
+		KubernetesServices:         []string{ts.URL},
+		MeasurementNameAsFieldName: true,
+	}
+	u, _ := url.Parse(ts.URL)
+	tsAddress := u.Hostname()
+
+	var acc testutil.Accumulator
+
+	err := acc.GatherError(p.Gather)
+	require.NoError(t, err)
+
+	assert.True(t, acc.HasFloatField("go_gc_duration_seconds", "go_gc_duration_seconds"))
+	assert.True(t, acc.HasFloatField("go_goroutines", "go_goroutines"))
+	assert.True(t, acc.HasFloatField("test_metric", "test_metric"))
+	assert.True(t, acc.HasTimestamp("test_metric", time.Unix(1490802350, 0)))
+	assert.True(t, acc.TagValue("test_metric", "address") == tsAddress)
+	assert.True(t, acc.TagValue("test_metric", "url") == ts.URL)
+}
+
 func TestPrometheusGeneratesMetricsAlthoughFirstDNSFails(t *testing.T) {
 	if testing.Short() {
 		t.Skip("Skipping integration test in short mode")