update readme

README.md

@@ -0,0 +1,27 @@
+# prometheus-exporter-merger
+
+Merges Prometheus metrics from multiple sources.
+
+## But Why?!
+
+> [prometheus/prometheus#3756](https://github.com/prometheus/prometheus/issues/3756)
+
+To start the exporter:
+
+```
+prometheus-exporter-merger --config config.yaml
+```
+
+Config example:
+
+```yaml
+listen: :8080
+scrap_timeout: 20s
+sources:
+  - url: http://127.0.0.1:8081/metrics
+    labels:
+      key1: value1
+  - url: http://127.0.0.1:8082/metrics
+    labels:
+      key2: value2
+```

cmd/config.go

@@ -13,9 +13,9 @@ type source struct {
 }
 
 type config struct {
-	Listen  string        `yaml:"listen"`
-	Timeout time.Duration `yaml:"timeout"`
-	Sources []*source     `yaml:"sources"`
+	Listen       string        `yaml:"listen"`
+	ScrapTimeout time.Duration `yaml:"scrap_timeout"`
+	Sources      []*source     `yaml:"sources"`
 }
 
 func parseConfig(filename string) (*config, error) {
@@ -24,8 +24,8 @@ func parseConfig(filename string) (*config, error) {
 		return nil, err
 	}
 	result := &config{
-		Listen:  ":8080",
-		Timeout: 15 * time.Second,
+		Listen:       ":8080",
+		ScrapTimeout: 15 * time.Second,
 	}
 	return result, yaml.Unmarshal(data, result)
 }

cmd/main.go

@@ -24,7 +24,7 @@ func Execute() {
 		panic(err)
 	}
 
-	m := merger.New(c.Timeout)
+	m := merger.New(c.ScrapTimeout)
 	for _, s := range c.Sources {
 		var labels []*prom.LabelPair
 		for k, v := range s.Labels {

merger/merger.go

@@ -16,18 +16,18 @@ type Merger interface {
 }
 
 type merger struct {
-	mu      sync.Mutex
-	timeout time.Duration
-	client  *http.Client
-	sources []*source
+	mu           sync.Mutex
+	scrapTimeout time.Duration
+	client       *http.Client
+	sources      []*source
 }
 
 type source struct {
 	url    string
 	labels []*prom.LabelPair
 }
 
-func New(timeout time.Duration) Merger {
+func New(scrapTimeout time.Duration) Merger {
 	client := &http.Client{
 		Transport: &http.Transport{
 			DisableKeepAlives:   false,
@@ -37,11 +37,11 @@ func New(timeout time.Duration) Merger {
 			MaxConnsPerHost:     10,
 			IdleConnTimeout:     5 * time.Minute,
 		},
-		Timeout: timeout,
+		Timeout: scrapTimeout,
 	}
 	return &merger{
-		timeout: timeout,
-		client:  client,
+		scrapTimeout: scrapTimeout,
+		client:       client,
 	}
 }
 
@@ -56,7 +56,7 @@ func (m *merger) AddSource(url string, labels []*prom.LabelPair) {
 func (m *merger) Merge(w io.Writer) error {
 	m.mu.Lock()
 	defer m.mu.Unlock()
-	ctx, cancel := context.WithTimeout(context.Background(), m.timeout)
+	ctx, cancel := context.WithTimeout(context.Background(), m.scrapTimeout)
 	defer cancel()
 	return m.merge(ctx, w)
 }