prometheusreceiver: change start time fallback from a config knob to a featuregate

This change creates an Alpha feature gate for this functionality since
this can be replaced when
open-telemetry#37186
is implemented.

Author: ridwanmsharif

.chloggen/starttime-fallback.yaml

@@ -7,7 +7,7 @@ change_type: enhancement
 component: prometheusreceiver
 
 # A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
-note: Add `UseCollectorStartTimeFallback` option for the start time metric adjuster to use the collector start time as an approximation of process start time as a fallback.
+note: Add `UseCollectorStartTimeFallback` featuregate for the start time metric adjuster to use the collector start time as an approximation of process start time as a fallback.
 
 # Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
 issues: [36364]

receiver/prometheusreceiver/README.md

@@ -67,7 +67,17 @@ prometheus --config.file=prom.yaml
 ```shell
 "--feature-gates=receiver.prometheusreceiver.UseCreatedMetric"
 ```
+- `receiver.prometheusreceiver.UseCollectorStartTimeFallback`:  enables using
+  the collector start time as the metric start time if the
+  process_start_time_seconds metric yields no result (for example if targets
+  expose no process_start_time_seconds metric). This is useful when the collector
+  start time is a good approximation of the process start time - for example in
+  serverless workloads when the collector is deployed as a sidecar. To enable it,
+  use the following feature gate option:
 
+```shell
+"--feature-gates=receiver.prometheusreceiver.UseCollectorStartTimeFallback"
+```
 - `receiver.prometheusreceiver.EnableNativeHistograms`: process and turn native histogram metrics into OpenTelemetry exponential histograms. For more details consult the [Prometheus native histograms](#prometheus-native-histograms) section.
 
 ```shell
@@ -119,7 +129,7 @@ The prometheus receiver also supports additional top-level options:
 - **trim_metric_suffixes**: [**Experimental**] When set to true, this enables trimming unit and some counter type suffixes from metric names. For example, it would cause `singing_duration_seconds_total` to be trimmed to `singing_duration`. This can be useful when trying to restore the original metric names used in OpenTelemetry instrumentation. Defaults to false.
 - **use_start_time_metric**: When set to true, this enables retrieving the start time of all counter metrics from the process_start_time_seconds metric. This is only correct if all counters on that endpoint started after the process start time, and the process is the only actor exporting the metric after the process started. It should not be used in "exporters" which export counters that may have started before the process itself. Use only if you know what you are doing, as this may result in incorrect rate calculations. Defaults to false.
 - **start_time_metric_regex**: The regular expression for the start time metric, and is only applied when use_start_time_metric is enabled.  Defaults to process_start_time_seconds.
-- **use_collector_start_time_fallback**: When set to true, this option enables using the collector start time as the metric start time if the process_start_time_seconds metric yields no result (for example if targets expose no process_start_time_seconds metric). This is useful when the collector start time is a good approximation of the process start time - for example in serverless workloads when the collector is deployed as a sidecar. This is only applied when use_start_time_metric is enabled. Defaults to false.
+
 For example,
 
 ```yaml
@@ -128,7 +138,6 @@ receivers:
       trim_metric_suffixes: true
       use_start_time_metric: true
       start_time_metric_regex: foo_bar_.*
-      use_collector_start_time_fallback: true
       config:
         scrape_configs:
           - job_name: 'otel-collector'

receiver/prometheusreceiver/config.go

@@ -24,17 +24,6 @@ type Config struct {
 	PrometheusConfig   *PromConfig `mapstructure:"config"`
 	TrimMetricSuffixes bool        `mapstructure:"trim_metric_suffixes"`
 
-	// Settings for adjusting metrics. Will default to using an InitialPointAdjuster
-	// which will use the first scraped point to define the start time for the timeseries.
-	AdjustOpts MetricAdjusterOpts `mapstructure:",squash"` // squash ensures fields are correctly decoded in embedded struct.
-
-	// ReportExtraScrapeMetrics - enables reporting of additional metrics for Prometheus client like scrape_body_size_bytes
-	ReportExtraScrapeMetrics bool `mapstructure:"report_extra_scrape_metrics"`
-
-	TargetAllocator *targetallocator.Config `mapstructure:"target_allocator"`
-}
-
-type MetricAdjusterOpts struct {
 	// UseStartTimeMetric enables retrieving the start time of all counter
 	// metrics from the process_start_time_seconds metric. This is only correct
 	// if all counters on that endpoint started after the process start time,
@@ -45,19 +34,10 @@ type MetricAdjusterOpts struct {
 	UseStartTimeMetric   bool   `mapstructure:"use_start_time_metric"`
 	StartTimeMetricRegex string `mapstructure:"start_time_metric_regex"`
 
-	// UseCollectorStartTimeFallback enables using a fallback start time if a
-	// start time is otherwise unavailable when adjusting metrics. This would
-	// happen if the UseStartTimeMetric is used but the application doesn't emit
-	// a process_start_time_seconds metric or a metric that matches the
-	// StartTimeMetricRegex provided.
-	//
-	// If enabled, the fallback start time used for adjusted metrics is an
-	// approximation of the collector start time.
-	//
-	// This option should be used when the collector start time is a good
-	// approximation of the process start time - for example in serverless
-	// workloads when the collector is deployed as a sidecar.
-	UseCollectorStartTimeFallback bool `mapstructure:"use_collector_start_time_fallback"`
+	// ReportExtraScrapeMetrics - enables reporting of additional metrics for Prometheus client like scrape_body_size_bytes
+	ReportExtraScrapeMetrics bool `mapstructure:"report_extra_scrape_metrics"`
+
+	TargetAllocator *targetallocator.Config `mapstructure:"target_allocator"`
 }
 
 // Validate checks the receiver configuration is valid.

receiver/prometheusreceiver/config_test.go

@@ -43,9 +43,9 @@ func TestLoadConfig(t *testing.T) {
 	r1 := cfg.(*Config)
 	assert.Equal(t, "demo", r1.PrometheusConfig.ScrapeConfigs[0].JobName)
 	assert.Equal(t, 5*time.Second, time.Duration(r1.PrometheusConfig.ScrapeConfigs[0].ScrapeInterval))
-	assert.True(t, r1.AdjustOpts.UseStartTimeMetric)
+	assert.True(t, r1.UseStartTimeMetric)
 	assert.True(t, r1.TrimMetricSuffixes)
-	assert.Equal(t, "^(.+_)*process_start_time_seconds$", r1.AdjustOpts.StartTimeMetricRegex)
+	assert.Equal(t, "^(.+_)*process_start_time_seconds$", r1.StartTimeMetricRegex)
 	assert.True(t, r1.ReportExtraScrapeMetrics)
 
 	assert.Equal(t, "http://my-targetallocator-service", r1.TargetAllocator.Endpoint)

receiver/prometheusreceiver/factory.go

@@ -33,6 +33,14 @@ var enableNativeHistogramsGate = featuregate.GlobalRegistry().MustRegister(
 		" those Prometheus classic histograms that have a native histogram alternative"),
 )
 
+var useCollectorStartTimeFallbackGate = featuregate.GlobalRegistry().MustRegister(
+	"receiver.prometheusreceiver.UseCollectorStartTimeFallback",
+	featuregate.StageAlpha,
+	featuregate.WithRegisterDescription("When enabled, the Prometheus receiver's"+
+		" start time metric adjuster will fallback to using the collector start time"+
+		" when a start time is not available"),
+)
+
 // NewFactory creates a new Prometheus receiver factory.
 func NewFactory() receiver.Factory {
 	return receiver.NewFactory(

receiver/prometheusreceiver/internal/starttimemetricadjuster.go

@@ -65,7 +65,7 @@ func (stma *startTimeMetricAdjuster) AdjustMetrics(metrics pmetric.Metrics) erro
 		if stma.fallbackStartTime == nil {
 			return err
 		}
-		stma.logger.Info("Couldn't get start time for metrics. Using fallback start time.", zap.Error(err))
+		stma.logger.Info("Couldn't get start time for metrics. Using fallback start time.", zap.Error(err), zap.Time("fallback_start_time", *stma.fallbackStartTime))
 		startTime = float64(stma.fallbackStartTime.Unix())
 	}
 

receiver/prometheusreceiver/metrics_receiver.go

@@ -123,8 +123,8 @@ func (r *pReceiver) initPrometheusComponents(ctx context.Context, logger log.Log
 	}()
 
 	var startTimeMetricRegex *regexp.Regexp
-	if r.cfg.AdjustOpts.StartTimeMetricRegex != "" {
-		startTimeMetricRegex, err = regexp.Compile(r.cfg.AdjustOpts.StartTimeMetricRegex)
+	if r.cfg.StartTimeMetricRegex != "" {
+		startTimeMetricRegex, err = regexp.Compile(r.cfg.StartTimeMetricRegex)
 		if err != nil {
 			return err
 		}
@@ -134,10 +134,10 @@ func (r *pReceiver) initPrometheusComponents(ctx context.Context, logger log.Log
 		r.consumer,
 		r.settings,
 		gcInterval(r.cfg.PrometheusConfig),
-		r.cfg.AdjustOpts.UseStartTimeMetric,
+		r.cfg.UseStartTimeMetric,
 		startTimeMetricRegex,
 		useCreatedMetricGate.IsEnabled(),
-		r.cfg.AdjustOpts.UseCollectorStartTimeFallback,
+		useCollectorStartTimeFallbackGate.IsEnabled(),
 		enableNativeHistogramsGate.IsEnabled(),
 		r.cfg.PrometheusConfig.GlobalConfig.ExternalLabels,
 		r.cfg.TrimMetricSuffixes,

receiver/prometheusreceiver/metrics_receiver_helper_test.go

@@ -687,8 +687,8 @@ func testComponent(t *testing.T, targets []*testData, alterConfig func(*Config),
 	defer mp.Close()
 
 	config := &Config{
-		PrometheusConfig: cfg,
-		AdjustOpts:       MetricAdjusterOpts{StartTimeMetricRegex: ""},
+		PrometheusConfig:     cfg,
+		StartTimeMetricRegex: "",
 	}
 	if alterConfig != nil {
 		alterConfig(config)

receiver/prometheusreceiver/metrics_receiver_report_extra_scrape_metrics_test.go

@@ -52,11 +52,9 @@ func testScraperMetrics(t *testing.T, targets []*testData, reportExtraScrapeMetr
 
 	cms := new(consumertest.MetricsSink)
 	receiver := newPrometheusReceiver(receivertest.NewNopSettings(), &Config{
-		PrometheusConfig: cfg,
-		AdjustOpts: MetricAdjusterOpts{
-			UseStartTimeMetric:   false,
-			StartTimeMetricRegex: "",
-		},
+		PrometheusConfig:         cfg,
+		UseStartTimeMetric:       false,
+		StartTimeMetricRegex:     "",
 		ReportExtraScrapeMetrics: reportExtraScrapeMetrics,
 	}, cms)
 

receiver/prometheusreceiver/metrics_receiver_test.go

@@ -1424,7 +1424,7 @@ func TestStartTimeMetric(t *testing.T) {
 		},
 	}
 	testComponent(t, targets, func(c *Config) {
-		c.AdjustOpts.UseStartTimeMetric = true
+		c.UseStartTimeMetric = true
 	})
 }
 
@@ -1475,8 +1475,8 @@ func TestStartTimeMetricRegex(t *testing.T) {
 		},
 	}
 	testComponent(t, targets, func(c *Config) {
-		c.AdjustOpts.StartTimeMetricRegex = "^(.+_)*process_start_time_seconds$"
-		c.AdjustOpts.UseStartTimeMetric = true
+		c.StartTimeMetricRegex = "^(.+_)*process_start_time_seconds$"
+		c.UseStartTimeMetric = true
 	})
 }
 

receiver/purefbreceiver/go.mod

@@ -48,6 +48,7 @@ require (
 	github.com/docker/docker v27.3.1+incompatible // indirect
 	github.com/docker/go-connections v0.4.0 // indirect
 	github.com/docker/go-units v0.5.0 // indirect
+	github.com/ebitengine/purego v0.8.1 // indirect
 	github.com/emicklei/go-restful/v3 v3.11.0 // indirect
 	github.com/envoyproxy/go-control-plane v0.13.1 // indirect
 	github.com/envoyproxy/protoc-gen-validate v1.1.0 // indirect
@@ -58,6 +59,7 @@ require (
 	github.com/go-logfmt/logfmt v0.6.0 // indirect
 	github.com/go-logr/logr v1.4.2 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/go-ole/go-ole v1.2.6 // indirect
 	github.com/go-openapi/jsonpointer v0.20.2 // indirect
 	github.com/go-openapi/jsonreference v0.20.4 // indirect
 	github.com/go-openapi/swag v0.22.9 // indirect
@@ -107,6 +109,7 @@ require (
 	github.com/kolo/xmlrpc v0.0.0-20220921171641-a4b6fa1dd06b // indirect
 	github.com/kylelemons/godebug v1.1.0 // indirect
 	github.com/linode/linodego v1.37.0 // indirect
+	github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0 // indirect
 	github.com/mailru/easyjson v0.7.7 // indirect
 	github.com/mattn/go-colorable v0.1.13 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
@@ -130,14 +133,19 @@ require (
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/planetscale/vtprotobuf v0.6.1-0.20240319094008-0393e58bdf10 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
+	github.com/power-devops/perfstat v0.0.0-20210106213030-5aafc221ea8c // indirect
 	github.com/prometheus/client_golang v1.20.5 // indirect
 	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/common/sigv4 v0.1.0 // indirect
 	github.com/prometheus/procfs v0.15.1 // indirect
 	github.com/rs/cors v1.11.1 // indirect
 	github.com/scaleway/scaleway-sdk-go v1.0.0-beta.29 // indirect
+	github.com/shirou/gopsutil/v4 v4.24.12 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
+	github.com/tklauser/go-sysconf v0.3.12 // indirect
+	github.com/tklauser/numcpus v0.6.1 // indirect
 	github.com/vultr/govultr/v2 v2.17.2 // indirect
+	github.com/yusufpapurcu/wmi v1.2.4 // indirect
 	go.opencensus.io v0.24.0 // indirect
 	go.opentelemetry.io/collector/client v1.23.1-0.20250119231113-f07ebc3afb51 // indirect
 	go.opentelemetry.io/collector/component/componentstatus v0.117.1-0.20250119231113-f07ebc3afb51 // indirect