[chore] Don't use prom server created by OpenCensus iniialization (#6890

)

Create the Prometheus HTTP handler explicitly to better separate responsibilities between OC and OTel instrumentation initializations and prepare for the eventual removal of the OC instrumentation

service/telemetry.go

@@ -25,6 +25,7 @@ import (
  ocprom "contrib.go.opencensus.io/exporter/prometheus"
  "github.com/google/uuid"
  "github.com/prometheus/client_golang/prometheus"
+ "github.com/prometheus/client_golang/prometheus/promhttp"
  ocmetric "go.opencensus.io/metric"
  "go.opencensus.io/metric/metricproducer"
  "go.opencensus.io/stats/view"
@@ -99,22 +100,18 @@ func (tel *telemetryInitializer) init(buildInfo component.BuildInfo, logger *zap
  return err
  }
 
- var pe http.Handler
- var err error
  // This prometheus registry is shared between OpenCensus and OpenTelemetry exporters,
  // acting as a bridge between OC and Otel.
  // This is used as a path to migrate the existing OpenCensus instrumentation
  // to the OpenTelemetry Go SDK without breaking existing metrics.
  promRegistry := prometheus.NewRegistry()
  if tel.registry.IsEnabled(obsreportconfig.UseOtelForInternalMetricsfeatureGateID) {
- err = tel.initOpenTelemetry(telAttrs, promRegistry)
- if err != nil {
+ if err := tel.initOpenTelemetry(telAttrs, promRegistry); err != nil {
  return err
  }
  }
 
- pe, err = tel.initOpenCensus(cfg, telAttrs, promRegistry)
- if err != nil {
+ if err := tel.initOpenCensus(cfg, telAttrs, promRegistry); err != nil {
  return err
  }
 
@@ -125,7 +122,7 @@ func (tel *telemetryInitializer) init(buildInfo component.BuildInfo, logger *zap
  )
 
  mux := http.NewServeMux()
- mux.Handle("/metrics", pe)
+ mux.Handle("/metrics", promhttp.HandlerFor(promRegistry, promhttp.HandlerOpts{}))
 
  tel.server = &http.Server{
  Addr: cfg.Metrics.Address,
@@ -172,13 +169,13 @@ func buildTelAttrs(buildInfo component.BuildInfo, cfg telemetry.Config) map[stri
  return telAttrs
 }
 
-func (tel *telemetryInitializer) initOpenCensus(cfg telemetry.Config, telAttrs map[string]string, promRegistry *prometheus.Registry) (http.Handler, error) {
+func (tel *telemetryInitializer) initOpenCensus(cfg telemetry.Config, telAttrs map[string]string, promRegistry *prometheus.Registry) error {
  tel.ocRegistry = ocmetric.NewRegistry()
  metricproducer.GlobalManager().AddProducer(tel.ocRegistry)
 
  tel.views = obsreportconfig.AllViews(cfg.Metrics.Level)
  if err := view.Register(tel.views...); err != nil {
- return nil, err
+ return err
  }
 
  // Until we can use a generic metrics exporter, default to Prometheus.
@@ -195,11 +192,11 @@ func (tel *telemetryInitializer) initOpenCensus(cfg telemetry.Config, telAttrs m
 
  pe, err := ocprom.NewExporter(opts)
  if err != nil {
- return nil, err
+ return err
  }
 
  view.RegisterExporter(pe)
- return pe, nil
+ return nil
 }
 
 func (tel *telemetryInitializer) initOpenTelemetry(attrs map[string]string, promRegistry prometheus.Registerer) error {