feat(xPrometheus): added header (#470)

CHANGELOG.md

@@ -9,6 +9,9 @@ Unreleased section should follow [Release Toolkit](https://github.com/newrelic/r
 
 ## Unreleased
 
+### Enhancement
+- Added XPrometheusHeader to allow exporters to give up complex computation when needed.
+
 ## v2.20.1 - 2024-01-03
 
 ### ⛓️ Dependencies
@@ -105,7 +108,7 @@ In particular, it was not possible having `lowDataMode=true` to filter out every
 
 ## 2.16.3
 ## Changed
-- Several dependencies updated 
+- Several dependencies updated
 - The `use_bearer` config is now exposed the config for static targets by @paologallinaharbur in https://github.com/newrelic/nri-prometheus/pull/327
 
 ## 2.16.2

configs/nri-prometheus-config.yml.sample

@@ -27,6 +27,7 @@ integrations:
       audit: false
 
       # The HTTP client timeout when fetching data from endpoints. Defaults to "5s" if it is not set.
+      # This timeout in seconds is passed as well as a X-Prometheus-Scrape-Timeout-Seconds header to the exporters
       # scrape_timeout: "5s"
 
       # Length in time to distribute the scraping from the endpoints. Default to "30s" if it is not set.

internal/integration/fetcher.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net/http"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -155,7 +156,7 @@ type prometheusFetcher struct {
 	httpClient    prometheus.HTTPDoer
 	bearerClient  prometheus.HTTPDoer
 	// Provides IoC for better testability. Its usual value is 'prometheus.Get'.
-	getMetrics func(httpClient prometheus.HTTPDoer, url string, acceptHeader string) (prometheus.MetricFamiliesByName, error)
+	getMetrics func(httpClient prometheus.HTTPDoer, url string, acceptHeader string, fetchTimeout string) (prometheus.MetricFamiliesByName, error)
 	log        *logrus.Entry
 }
 
@@ -253,7 +254,8 @@ func (pf *prometheusFetcher) fetch(t endpoints.Target) (prometheus.MetricFamilie
 		httpClient = pf.bearerClient
 	}
 
-	mfs, err := pf.getMetrics(httpClient, t.URL.String(), pf.acceptHeader)
+	ft := strconv.FormatFloat(pf.fetchTimeout.Seconds(), 'f', -1, 64)
+	mfs, err := pf.getMetrics(httpClient, t.URL.String(), pf.acceptHeader, ft)
 	timer.ObserveDuration()
 	if err != nil {
 		pf.log.WithError(err).Warnf("fetching Prometheus metrics: %s (%s)", t.URL.String(), t.Object.Name)

internal/integration/fetcher_test.go

@@ -4,7 +4,10 @@
 package integration
 
 import (
+	"bytes"
 	"fmt"
+	"io"
+	"net/http"
 	"net/url"
 	"strings"
 	"sync/atomic"
@@ -24,17 +27,58 @@ import (
 const (
 	fetchDuration = 1 * time.Millisecond
 	fetchTimeout  = time.Second * 5
+	testAccept    = "this-is-a-test"
 	workerThreads = 4
 	queueLength   = 100
 )
 
+type mockClient struct {
+	recordedHeader http.Header
+}
+
+func (m *mockClient) Do(req *http.Request) (*http.Response, error) {
+	m.recordedHeader = req.Header
+	return &http.Response{
+		StatusCode: 200,
+		Body:       io.NopCloser(bytes.NewReader([]byte(""))),
+	}, nil
+}
+
+func TestXHeader(t *testing.T) {
+	mClient := mockClient{}
+	fetcher := NewFetcher(fetchDuration, fetchTimeout, "this-is-a-test", workerThreads, "", "", true, queueLength)
+	fetcher.(*prometheusFetcher).httpClient = &mClient
+
+	pairsCh := fetcher.Fetch([]endpoints.Target{
+		{
+			URL: url.URL{Scheme: "http", Path: "hello/metrics"},
+		},
+	})
+
+	select {
+	case <-pairsCh:
+	case <-time.After(fetchTimeout):
+		t.Fatal("can't fetch data")
+	}
+
+	accept := mClient.recordedHeader.Get(prometheus.AcceptHeader)
+	if accept != testAccept {
+		t.Errorf("Expected Accept header %q, got %q", testAccept, accept)
+	}
+
+	xPrometheus := mClient.recordedHeader.Get(prometheus.XPrometheusScrapeTimeoutHeader)
+	if xPrometheus != "5" {
+		t.Errorf("Expected xPrometheus header %q, got %q", "5", xPrometheus)
+	}
+}
+
 func TestFetcher(t *testing.T) {
 	t.Parallel()
 
 	// Given a fetcher
 	fetcher := NewFetcher(fetchDuration, fetchTimeout, "", workerThreads, "", "", true, queueLength)
 	var invokedURL string
-	fetcher.(*prometheusFetcher).getMetrics = func(client prometheus.HTTPDoer, url string, _ string) (names prometheus.MetricFamiliesByName, e error) {
+	fetcher.(*prometheusFetcher).getMetrics = func(client prometheus.HTTPDoer, url string, _ string, _ string) (names prometheus.MetricFamiliesByName, e error) {
 		invokedURL = url
 		return prometheus.MetricFamiliesByName{
 			"some-name": dto.MetricFamily{},
@@ -73,7 +117,7 @@ func TestFetcher_Error(t *testing.T) {
 
 	// That fails retrieving data from one of the metrics endpoint
 	invokedURLs := make([]string, 0)
-	fetcher.(*prometheusFetcher).getMetrics = func(client prometheus.HTTPDoer, url string, _ string) (names prometheus.MetricFamiliesByName, e error) {
+	fetcher.(*prometheusFetcher).getMetrics = func(client prometheus.HTTPDoer, url string, _ string, _ string) (names prometheus.MetricFamiliesByName, e error) {
 		if strings.Contains(url, "fail") {
 			return nil, errors.New("catapun")
 		}
@@ -125,7 +169,7 @@ func TestFetcher_ConcurrencyLimit(t *testing.T) {
 	// Given a Fetcher
 	fetcher := NewFetcher(time.Millisecond, fetchTimeout, "", workerThreads, "", "", true, queueLength)
 
-	fetcher.(*prometheusFetcher).getMetrics = func(client prometheus.HTTPDoer, url string, _ string) (names prometheus.MetricFamiliesByName, e error) {
+	fetcher.(*prometheusFetcher).getMetrics = func(client prometheus.HTTPDoer, url string, _ string, _ string) (names prometheus.MetricFamiliesByName, e error) {
 		defer atomic.AddInt32(&parallelTasks, -1)
 		atomic.AddInt32(&parallelTasks, 1)
 		reportedParallel <- atomic.LoadInt32(&parallelTasks)

internal/pkg/prometheus/prometheus.go

@@ -36,15 +36,23 @@ func ResetTargetSize() {
 	targetSize.Reset()
 }
 
+const (
+	// XPrometheusScrapeTimeoutHeader included in all requests. It informs exporters about its timeout.
+	XPrometheusScrapeTimeoutHeader = "X-Prometheus-Scrape-Timeout-Seconds"
+	// AcceptHeader included in all requests
+	AcceptHeader = "Accept"
+)
+
 // Get scrapes the given URL and decodes the retrieved payload.
-func Get(client HTTPDoer, url string, acceptHeader string) (MetricFamiliesByName, error) {
+func Get(client HTTPDoer, url string, acceptHeader string, fetchTimeout string) (MetricFamiliesByName, error) {
 	mfs := MetricFamiliesByName{}
 	req, err := http.NewRequest("GET", url, nil)
 	if err != nil {
 		return mfs, err
 	}
 
-	req.Header.Add("Accept", acceptHeader)
+	req.Header.Add(AcceptHeader, acceptHeader)
+	req.Header.Add(XPrometheusScrapeTimeoutHeader, fetchTimeout)
 
 	resp, err := client.Do(req)
 	if err != nil {

internal/pkg/prometheus/prometheus_test.go

@@ -15,18 +15,25 @@ import (
 const testHeader = "application/openmetrics-text"
 
 func TestGetHeader(t *testing.T) {
+	fetchTimeout := "15"
+
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		accept := r.Header.Get("Accept")
+		accept := r.Header.Get(prometheus.AcceptHeader)
 		if accept != testHeader {
 			t.Errorf("Expected Accept header %s, got %q", testHeader, accept)
 		}
 
+		xPrometheus := r.Header.Get(prometheus.XPrometheusScrapeTimeoutHeader)
+		if xPrometheus != fetchTimeout {
+			t.Errorf("Expected xPrometheus header %s, got %q", xPrometheus, fetchTimeout)
+		}
+
 		_, _ = w.Write([]byte("metric_a 1\nmetric_b 2\n"))
 	}))
 	defer ts.Close()
 
 	expected := []string{"metric_a", "metric_b"}
-	mfs, err := prometheus.Get(http.DefaultClient, ts.URL, testHeader)
+	mfs, err := prometheus.Get(http.DefaultClient, ts.URL, testHeader, fetchTimeout)
 	actual := []string{}
 	for k := range mfs {
 		actual = append(actual, k)