Merge pull request #118820 from logicalhan/processstart

Write process start time to prometheus options so that scraping clients can parse it first

staging/src/k8s.io/component-base/metrics/http.go

@@ -19,19 +19,28 @@ package metrics
 import (
 	"io"
 	"net/http"
+	"time"
 
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
+var (
+	processStartedAt time.Time
+)
+
+func init() {
+	processStartedAt = time.Now()
+}
+
 // These constants cause handlers serving metrics to behave as described if
 // errors are encountered.
 const (
-	// Serve an HTTP status code 500 upon the first error
+	// HTTPErrorOnError serve an HTTP status code 500 upon the first error
 	// encountered. Report the error message in the body.
 	HTTPErrorOnError promhttp.HandlerErrorHandling = iota
 
-	// Ignore errors and try to serve as many metrics as possible.  However,
-	// if no metrics can be served, serve an HTTP status code 500 and the
+	// ContinueOnError ignore errors and try to serve as many metrics as possible.
+	// However, if no metrics can be served, serve an HTTP status code 500 and the
 	// last error message in the body. Only use this in deliberate "best
 	// effort" metrics collection scenarios. In this case, it is highly
 	// recommended to provide other means of detecting errors: By setting an
@@ -41,7 +50,7 @@ const (
 	// alerts.
 	ContinueOnError
 
-	// Panic upon the first error encountered (useful for "crash only" apps).
+	// PanicOnError panics upon the first error encountered (useful for "crash only" apps).
 	PanicOnError
 )
 
@@ -50,6 +59,7 @@ const (
 type HandlerOpts promhttp.HandlerOpts
 
 func (ho *HandlerOpts) toPromhttpHandlerOpts() promhttp.HandlerOpts {
+	ho.ProcessStartTime = processStartedAt
 	return promhttp.HandlerOpts(*ho)
 }
 

staging/src/k8s.io/component-base/metrics/legacyregistry/registry.go

@@ -18,6 +18,7 @@ package legacyregistry
 
 import (
 	"net/http"
+	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/collectors"
@@ -45,19 +46,22 @@ var (
 
 	// Registerer exposes the global registerer
 	Registerer = defaultRegistry.Registerer
+
+	processStart time.Time
 )
 
 func init() {
 	RawMustRegister(collectors.NewProcessCollector(collectors.ProcessCollectorOpts{}))
 	RawMustRegister(collectors.NewGoCollector(collectors.WithGoCollectorRuntimeMetrics(collectors.MetricsAll)))
 	defaultRegistry.RegisterMetaMetrics()
+	processStart = time.Now()
 }
 
 // Handler returns an HTTP handler for the DefaultGatherer. It is
 // already instrumented with InstrumentHandler (using "prometheus" as handler
 // name).
 func Handler() http.Handler {
-	return promhttp.InstrumentMetricHandler(prometheus.DefaultRegisterer, promhttp.HandlerFor(defaultRegistry, promhttp.HandlerOpts{}))
+	return promhttp.InstrumentMetricHandler(prometheus.DefaultRegisterer, promhttp.HandlerFor(defaultRegistry, promhttp.HandlerOpts{ProcessStartTime: processStart}))
 }
 
 // HandlerWithReset returns an HTTP handler for the DefaultGatherer but invokes
@@ -65,7 +69,7 @@ func Handler() http.Handler {
 func HandlerWithReset() http.Handler {
 	return promhttp.InstrumentMetricHandler(
 		prometheus.DefaultRegisterer,
-		metrics.HandlerWithReset(defaultRegistry, metrics.HandlerOpts{}))
+		metrics.HandlerWithReset(defaultRegistry, metrics.HandlerOpts{ProcessStartTime: processStart}))
 }
 
 // CustomRegister registers a custom collector but uses the global registry.

staging/src/k8s.io/component-base/metrics/legacyregistry/registry_test.go

@@ -0,0 +1,43 @@
+/*
+Copyright 2023 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package legacyregistry
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strconv"
+	"testing"
+	"time"
+)
+
+const (
+	processStartTimeHeader = "Process-Start-Time-Unix"
+)
+
+func TestProcessStartTimeHeader(t *testing.T) {
+	now := time.Now()
+	handler := Handler()
+
+	request, _ := http.NewRequest("GET", "/", nil)
+	writer := httptest.NewRecorder()
+	handler.ServeHTTP(writer, request)
+	got := writer.Header().Get(processStartTimeHeader)
+	gotInt, _ := strconv.ParseInt(got, 10, 64)
+	if gotInt != now.Unix() {
+		t.Errorf("got %d, wanted %d", gotInt, now.Unix())
+	}
+}