feat(outputs.loki): Add option for metric name label (#13157)

plugins/outputs/loki/README.md

@@ -52,4 +52,10 @@ to use them.
   # tls_ca = "/etc/telegraf/ca.pem"
   # tls_cert = "/etc/telegraf/cert.pem"
   # tls_key = "/etc/telegraf/key.pem"
+
+  ## Metric Name Label
+  ## Label to use for the metric name to when sending metrics. If set to an
+  ## empty string, this will not add the label. This is NOT suggested as there
+  ## is no way to differentiate between multiple metrics.
+  # metric_name_label = "__name"
 ```

plugins/outputs/loki/loki.go

@@ -32,17 +32,18 @@ const (
 )
 
 type Loki struct {
-	Domain       string            `toml:"domain"`
+	Domain          string            `toml:"domain"`
-	Endpoint     string            `toml:"endpoint"`
+	Endpoint        string            `toml:"endpoint"`
-	Timeout      config.Duration   `toml:"timeout"`
+	Timeout         config.Duration   `toml:"timeout"`
-	Username     config.Secret     `toml:"username"`
+	Username        config.Secret     `toml:"username"`
-	Password     config.Secret     `toml:"password"`
+	Password        config.Secret     `toml:"password"`
-	Headers      map[string]string `toml:"http_headers"`
+	Headers         map[string]string `toml:"http_headers"`
-	ClientID     string            `toml:"client_id"`
+	ClientID        string            `toml:"client_id"`
-	ClientSecret string            `toml:"client_secret"`
+	ClientSecret    string            `toml:"client_secret"`
-	TokenURL     string            `toml:"token_url"`
+	TokenURL        string            `toml:"token_url"`
-	Scopes       []string          `toml:"scopes"`
+	Scopes          []string          `toml:"scopes"`
-	GZipRequest  bool              `toml:"gzip_request"`
+	GZipRequest     bool              `toml:"gzip_request"`
+	MetricNameLabel string            `toml:"metric_name_label"`
 
 	url    string
 	client *http.Client
@@ -119,7 +120,9 @@ func (l *Loki) Write(metrics []telegraf.Metric) error {
 	})
 
 	for _, m := range metrics {
-		m.AddTag("__name", m.Name())
+		if l.MetricNameLabel != "" {
+			m.AddTag(l.MetricNameLabel, m.Name())
+		}
 
 		tags := m.TagList()
 		var line string
@@ -197,6 +200,8 @@ func (l *Loki) writeMetrics(s Streams) error {
 
 func init() {
 	outputs.Add("loki", func() telegraf.Output {
-		return &Loki{}
+		return &Loki{
+			MetricNameLabel: "__name",
+		}
 	})
 }

plugins/outputs/loki/loki_test.go

@@ -121,8 +121,7 @@ func TestStatusCode(t *testing.T) {
 				w.WriteHeader(tt.statusCode)
 			})
 
-			err = tt.plugin.Connect()
+			require.NoError(t, tt.plugin.Connect())
-			require.NoError(t, err)
 
 			err = tt.plugin.Write([]telegraf.Metric{getMetric()})
 			tt.errFunc(t, err)
@@ -167,8 +166,7 @@ func TestContentType(t *testing.T) {
 				w.WriteHeader(http.StatusOK)
 			})
 
-			err = tt.plugin.Connect()
+			require.NoError(t, tt.plugin.Connect())
-			require.NoError(t, err)
 
 			err = tt.plugin.Write([]telegraf.Metric{getMetric()})
 			require.NoError(t, err)
@@ -226,7 +224,7 @@ func TestContentEncodingGzip(t *testing.T) {
 				require.Len(t, s.Streams, 1)
 				require.Len(t, s.Streams[0].Logs, 1)
 				require.Len(t, s.Streams[0].Logs[0], 2)
-				require.Equal(t, map[string]string{"__name": "log", "key1": "value1"}, s.Streams[0].Labels)
+				require.Equal(t, map[string]string{"key1": "value1"}, s.Streams[0].Labels)
 				require.Equal(t, "123000000000", s.Streams[0].Logs[0][0])
 				require.Contains(t, s.Streams[0].Logs[0][1], "line=\"my log\"")
 				require.Contains(t, s.Streams[0].Logs[0][1], "field=\"3.14\"")
@@ -234,8 +232,7 @@ func TestContentEncodingGzip(t *testing.T) {
 				w.WriteHeader(http.StatusNoContent)
 			})
 
-			err = tt.plugin.Connect()
+			require.NoError(t, tt.plugin.Connect())
-			require.NoError(t, err)
 
 			err = tt.plugin.Write([]telegraf.Metric{getMetric()})
 			require.NoError(t, err)
@@ -243,6 +240,56 @@ func TestContentEncodingGzip(t *testing.T) {
 	}
 }
 
+func TestMetricNameLabel(t *testing.T) {
+	ts := httptest.NewServer(http.NotFoundHandler())
+	defer ts.Close()
+
+	u, err := url.Parse(fmt.Sprintf("http://%s", ts.Listener.Addr().String()))
+	require.NoError(t, err)
+
+	tests := []struct {
+		name            string
+		metricNameLabel string
+	}{
+		{
+			name:            "no label",
+			metricNameLabel: "",
+		},
+		{
+			name:            "custom label",
+			metricNameLabel: "foobar",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ts.Config.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				payload, err := io.ReadAll(r.Body)
+				require.NoError(t, err)
+
+				var s Request
+				require.NoError(t, json.Unmarshal(payload, &s))
+
+				switch tt.metricNameLabel {
+				case "":
+					require.Equal(t, map[string]string{"key1": "value1"}, s.Streams[0].Labels)
+				case "foobar":
+					require.Equal(t, map[string]string{"foobar": "log", "key1": "value1"}, s.Streams[0].Labels)
+				}
+
+				w.WriteHeader(http.StatusNoContent)
+			})
+
+			l := Loki{
+				Domain:          u.String(),
+				MetricNameLabel: tt.metricNameLabel,
+			}
+			require.NoError(t, l.Connect())
+			require.NoError(t, l.Write([]telegraf.Metric{getMetric()}))
+		})
+	}
+}
+
 func TestBasicAuth(t *testing.T) {
 	ts := httptest.NewServer(http.NotFoundHandler())
 	defer ts.Close()
@@ -349,8 +396,7 @@ func TestOAuthClientCredentialsGrant(t *testing.T) {
 				}
 			})
 
-			err = tt.plugin.Connect()
+			require.NoError(t, tt.plugin.Connect())
-			require.NoError(t, err)
 
 			err = tt.plugin.Write([]telegraf.Metric{getMetric()})
 			require.NoError(t, err)
@@ -375,8 +421,7 @@ func TestDefaultUserAgent(t *testing.T) {
 			Domain: u.String(),
 		}
 
-		err = client.Connect()
+		require.NoError(t, client.Connect())
-		require.NoError(t, err)
 
 		err = client.Write([]telegraf.Metric{getMetric()})
 		require.NoError(t, err)
@@ -404,7 +449,7 @@ func TestMetricSorting(t *testing.T) {
 			require.Len(t, s.Streams, 1)
 			require.Len(t, s.Streams[0].Logs, 2)
 			require.Len(t, s.Streams[0].Logs[0], 2)
-			require.Equal(t, map[string]string{"__name": "log", "key1": "value1"}, s.Streams[0].Labels)
+			require.Equal(t, map[string]string{"key1": "value1"}, s.Streams[0].Labels)
 			require.Equal(t, "456000000000", s.Streams[0].Logs[0][0])
 			require.Contains(t, s.Streams[0].Logs[0][1], "line=\"older log\"")
 			require.Contains(t, s.Streams[0].Logs[0][1], "field=\"3.14\"")
@@ -419,8 +464,7 @@ func TestMetricSorting(t *testing.T) {
 			Domain: u.String(),
 		}
 
-		err = client.Connect()
+		require.NoError(t, client.Connect())
-		require.NoError(t, err)
 
 		err = client.Write(getOutOfOrderMetrics())
 		require.NoError(t, err)

plugins/outputs/loki/sample.conf

@@ -23,3 +23,9 @@
   # tls_ca = "/etc/telegraf/ca.pem"
   # tls_cert = "/etc/telegraf/cert.pem"
   # tls_key = "/etc/telegraf/key.pem"
+
+  ## Metric Name Label
+  ## Label to use for the metric name to when sending metrics. If set to an
+  ## empty string, this will not add the label. This is NOT suggested as there
+  ## is no way to differentiate between multiple metrics.
+  # metric_name_label = "__name"