Provide an InstrumentedHandler
See https://github.com/prometheus/client_golang/issues/316 for details.
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@ -61,9 +61,8 @@ func giveBuf(buf *bytes.Buffer) {
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// name).
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//
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// Deprecated: Please note the issues described in the doc comment of
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// InstrumentHandler. You might want to consider using promhttp.Handler instead
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// (which is not instrumented, but can be instrumented with the tooling provided
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// in package promhttp).
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// InstrumentHandler. You might want to consider using
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// promhttp.InstrumentedHandler instead.
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func Handler() http.Handler {
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return InstrumentHandler("prometheus", UninstrumentedHandler())
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}
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@ -67,19 +67,32 @@ func giveBuf(buf *bytes.Buffer) {
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bufPool.Put(buf)
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}
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// Handler returns an HTTP handler for the prometheus.DefaultGatherer. The
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// Handler uses the default HandlerOpts, i.e. report the first error as an HTTP
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// error, no error logging, and compression if requested by the client.
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// Handler returns an http.Handler for the prometheus.DefaultGatherer, using
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// default HandlerOpts, i.e. it reports the first error as an HTTP error, it has
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// no error logging, and it applies compression if requested by the client.
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//
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// If you want to create a Handler for the DefaultGatherer with different
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// HandlerOpts, create it with HandlerFor with prometheus.DefaultGatherer and
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// your desired HandlerOpts.
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// The returned http.Handler is already instrumented using the
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// InstrumentMetricHandler function and the prometheus.DefaultRegisterer. If you
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// create multiple http.Handlers by separate calls of the Handler function, the
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// metrics used for instrumentation will be shared between them, providing
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// global scrape counts.
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//
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// This function is meant to cover the bulk of basic use cases. If you are doing
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// anything that requires more customization (including using a non-default
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// Gatherer, different instrumentation, and non-default HandlerOpts), use the
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// HandlerFor function. See there for details.
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func Handler() http.Handler {
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return HandlerFor(prometheus.DefaultGatherer, HandlerOpts{})
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return InstrumentMetricHandler(
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prometheus.DefaultRegisterer, HandlerFor(prometheus.DefaultGatherer, HandlerOpts{}),
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)
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}
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// HandlerFor returns an http.Handler for the provided Gatherer. The behavior
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// of the Handler is defined by the provided HandlerOpts.
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// HandlerFor returns an uninstrumented http.Handler for the provided
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// Gatherer. The behavior of the Handler is defined by the provided
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// HandlerOpts. Thus, HandlerFor is useful to create http.Handlers for custom
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// Gatherers, with non-default HandlerOpts, and/or with custom (or no)
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// instrumentation. Use the InstrumentMetricHandler function to apply the same
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// kind of instrumentation as it is used by the Handler function.
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func HandlerFor(reg prometheus.Gatherer, opts HandlerOpts) http.Handler {
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return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
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mfs, err := reg.Gather()
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@ -142,6 +155,56 @@ func HandlerFor(reg prometheus.Gatherer, opts HandlerOpts) http.Handler {
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})
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}
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// InstrumentMetricHandler is usually used with an http.Handler returned by the
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// HandlerFor function. It instruments the provided http.Handler with two
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// metrics: A counter vector "promhttp_metric_handler_requests_total" to count
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// scrapes partitioned by HTTP status code, and a gauge
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// "promhttp_metric_handler_requests_in_flight" to track the number of
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// simultaneous scrapes. This function idempotently registers collectors for
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// both metrics with the provided Registerer. It panics if the registration
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// fails. The provided metrics are useful to see how many scrapes hit the
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// monitored target (which could be from different Prometheus servers or other
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// scrapers), and how often they overlap (which would result in more than one
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// scrape in flight at the same time). Note that the scrapes-in-flight gauge
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// will contain the scrape by which it is exposed, while the scrape counter will
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// only get incremented after the scrape is complete (as only then the status
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// code is known). For tracking scrape durations, use the
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// "scrape_duration_seconds" gauge created by the Prometheus server upon each
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// scrape.
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func InstrumentMetricHandler(reg prometheus.Registerer, handler http.Handler) http.Handler {
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cnt := prometheus.NewCounterVec(
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prometheus.CounterOpts{
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Name: "promhttp_metric_handler_requests_total",
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Help: "Total number of scrapes by HTTP status code.",
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},
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[]string{"code"},
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)
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// Initialize the most likely HTTP status codes.
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cnt.WithLabelValues("200")
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cnt.WithLabelValues("500")
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if err := reg.Register(cnt); err != nil {
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if are, ok := err.(prometheus.AlreadyRegisteredError); ok {
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cnt = are.ExistingCollector.(*prometheus.CounterVec)
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} else {
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panic(err)
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}
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}
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gge := prometheus.NewGauge(prometheus.GaugeOpts{
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Name: "promhttp_metric_handler_requests_in_flight",
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Help: "Current number of scrapes being served.",
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})
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if err := reg.Register(gge); err != nil {
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if are, ok := err.(prometheus.AlreadyRegisteredError); ok {
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gge = are.ExistingCollector.(prometheus.Gauge)
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} else {
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panic(err)
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}
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}
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return InstrumentHandlerCounter(cnt, InstrumentHandlerInFlight(gge, handler))
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}
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// HandlerErrorHandling defines how a Handler serving metrics will handle
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// errors.
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type HandlerErrorHandling int
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@ -19,6 +19,7 @@ import (
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"log"
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"net/http"
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"net/http/httptest"
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"strings"
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"testing"
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"github.com/prometheus/client_golang/prometheus"
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@ -129,3 +130,42 @@ the_count 0
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}()
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panicHandler.ServeHTTP(writer, request)
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}
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func TestInstrumentMetricHandler(t *testing.T) {
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reg := prometheus.NewRegistry()
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handler := InstrumentMetricHandler(reg, HandlerFor(reg, HandlerOpts{}))
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// Do it again to test idempotency.
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InstrumentMetricHandler(reg, HandlerFor(reg, HandlerOpts{}))
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writer := httptest.NewRecorder()
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request, _ := http.NewRequest("GET", "/", nil)
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request.Header.Add("Accept", "test/plain")
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handler.ServeHTTP(writer, request)
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if got, want := writer.Code, http.StatusOK; got != want {
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t.Errorf("got HTTP status code %d, want %d", got, want)
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}
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want := "promhttp_metric_handler_requests_in_flight 1\n"
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if got := writer.Body.String(); !strings.Contains(got, want) {
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t.Errorf("got body %q, does not contain %q", got, want)
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}
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want = "promhttp_metric_handler_requests_total{code=\"200\"} 0\n"
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if got := writer.Body.String(); !strings.Contains(got, want) {
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t.Errorf("got body %q, does not contain %q", got, want)
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}
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writer.Body.Reset()
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handler.ServeHTTP(writer, request)
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if got, want := writer.Code, http.StatusOK; got != want {
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t.Errorf("got HTTP status code %d, want %d", got, want)
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}
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want = "promhttp_metric_handler_requests_in_flight 1\n"
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if got := writer.Body.String(); !strings.Contains(got, want) {
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t.Errorf("got body %q, does not contain %q", got, want)
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}
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want = "promhttp_metric_handler_requests_total{code=\"200\"} 1\n"
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if got := writer.Body.String(); !strings.Contains(got, want) {
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t.Errorf("got body %q, does not contain %q", got, want)
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}
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}
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