From f72c2c2b7d298c1b743320e572321ba5d4789a9e Mon Sep 17 00:00:00 2001
From: Han Kang <hankang@google.com>
Date: Tue, 20 Jun 2023 10:13:31 -0700
Subject: [PATCH] add process start to prometheus handler opts

---
 .../src/k8s.io/component-base/metrics/http.go  | 18 ++++++++++++++----
 .../metrics/legacyregistry/registry.go         |  8 ++++++--
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/staging/src/k8s.io/component-base/metrics/http.go b/staging/src/k8s.io/component-base/metrics/http.go
index 3394a8f7114..2a0d249c205 100644
--- a/staging/src/k8s.io/component-base/metrics/http.go
+++ b/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)
 }
 
diff --git a/staging/src/k8s.io/component-base/metrics/legacyregistry/registry.go b/staging/src/k8s.io/component-base/metrics/legacyregistry/registry.go
index 79c806d8b2a..64a430b7964 100644
--- a/staging/src/k8s.io/component-base/metrics/legacyregistry/registry.go
+++ b/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.