Updated metricsbuilder package to support only Prometheus as the metr…

…ics backend

internal/metrics/metricsbuilder/builder.go

@@ -17,16 +17,13 @@ package metricsbuilder
 
 import (
  "errors"
- "expvar"
  "flag"
- "log"
  "net/http"
 
  "github.com/prometheus/client_golang/prometheus"
  "github.com/prometheus/client_golang/prometheus/promhttp"
  "github.com/spf13/viper"
 
- jexpvar "github.com/jaegertracing/jaeger/internal/metrics/expvar"
  jprom "github.com/jaegertracing/jaeger/internal/metrics/prometheus"
  "github.com/jaegertracing/jaeger/pkg/metrics"
 )
@@ -47,14 +44,14 @@ type Builder struct {
  handler http.Handler
 }
 
-const expvarDepr = "(deprecated, will be removed after 2024-01-01 or in release v1.53.0, whichever is later) "
+// const expvarDepr = "(deprecated, will be removed after 2024-01-01 or in release v1.53.0, whichever is later) "
 
 // AddFlags adds flags for Builder.
 func AddFlags(flags *flag.FlagSet) {
  flags.String(
  metricsBackend,
  defaultMetricsBackend,
- "Defines which metrics backend to use for metrics reporting: prometheus, none, or expvar "+expvarDepr)
+ "Defines which metrics backend to use for metrics reporting: prometheus or none")
  flags.String(
  metricsHTTPRoute,
  defaultMetricsRoute,
@@ -78,10 +75,7 @@ func (b *Builder) CreateMetricsFactory(namespace string) (metrics.Factory, error
  return metricsFactory, nil
  }
  if b.Backend == "expvar" {
- metricsFactory := jexpvar.NewFactory(10).Namespace(metrics.NSOptions{Name: namespace, Tags: nil})
- b.handler = expvar.Handler()
- log.Printf("using expvar as metrics backend " + expvarDepr)
- return metricsFactory, nil
+ return nil, errors.New("expvar metrics backend is deprecated and no longer supported")
  }
  if b.Backend == "none" || b.Backend == "" {
  return metrics.NullFactory, nil

internal/metrics/metricsbuilder/builder_test.go

@@ -16,7 +16,6 @@
 package metricsbuilder
 
 import (
- "expvar"
  "flag"
  "testing"
 
@@ -61,29 +60,13 @@ func TestBuilder(t *testing.T) {
  }
  t.FailNow()
  }
- assertExpVarCounter := func() {
- var found expvar.KeyValue
- expected := "foo.counter"
- expvar.Do(func(kv expvar.KeyValue) {
- if kv.Key == expected {
- found = kv
- }
- })
- assert.Equal(t, expected, found.Key)
- }
  testCases := []struct {
  backend string
  route string
  err error
  handler bool
  assert func()
  }{
- {
- backend: "expvar",
- route: "/",
- handler: true,
- assert: assertExpVarCounter,
- },
  {
  backend: "prometheus",
  route: "/",