only register metric for new frontendProcessor (#3526)

* only register metric for new frontendProcessor

* fix test

* fix panic in tests

modules/querier/worker/frontend_processor.go

@@ -29,18 +29,18 @@ var processorBackoffConfig = backoff.Config{
 	MaxBackoff: 1 * time.Second,
 }
 
-var metricWorkerRequests = promauto.NewCounter(prometheus.CounterOpts{
-	Namespace: "tempo",
-	Name:      "querier_worker_request_executed_total",
-	Help:      "The total number of requests executed by the querier worker.",
-})
-
 func newFrontendProcessor(cfg Config, handler RequestHandler, log log.Logger) processor {
+	metricWorkerRequests := promauto.NewCounter(prometheus.CounterOpts{
+		Namespace: "tempo",
+		Name:      "querier_worker_request_executed_total",
+		Help:      "The total number of requests executed by the querier worker.",
+	})
 	return &frontendProcessor{
-		log:            log,
-		handler:        handler,
-		maxMessageSize: cfg.GRPCClientConfig.MaxSendMsgSize,
-		querierID:      cfg.QuerierID,
+		log:                 log,
+		handler:             handler,
+		maxMessageSize:      cfg.GRPCClientConfig.MaxSendMsgSize,
+		querierID:           cfg.QuerierID,
+		metricRequestsTotal: metricWorkerRequests,
 	}
 }
 
@@ -50,7 +50,8 @@ type frontendProcessor struct {
 	maxMessageSize int
 	querierID      string
 
-	log log.Logger
+	metricRequestsTotal prometheus.Counter
+	log                 log.Logger
 }
 
 // notifyShutdown implements processor.
@@ -193,7 +194,7 @@ func (fp *frontendProcessor) runRequest(ctx context.Context, request *httpgrpc.H
 		level.Error(fp.log).Log("msg", "error processing query", "err", errMsg)
 	}
 
-	metricWorkerRequests.Inc()
+	fp.metricRequestsTotal.Inc()
 
 	return response
 }

modules/querier/worker/frontend_processor_test.go

@@ -11,6 +11,7 @@ import (
 	"github.com/go-kit/log"
 	"github.com/grafana/dskit/grpcclient"
 	"github.com/grafana/dskit/httpgrpc"
+	"github.com/prometheus/client_golang/prometheus"
 	dto "github.com/prometheus/client_model/go"
 	"github.com/stretchr/testify/require"
 )
@@ -32,6 +33,8 @@ func TestRunRequests(t *testing.T) {
 
 	inf := newFrontendProcessor(Config{GRPCClientConfig: grpcclient.Config{MaxSendMsgSize: 10}}, RequestHandlerFunc(handler), log.NewNopLogger())
 	fp := inf.(*frontendProcessor)
+	// unregister metric in test avoid panic due to registering it twice in tests
+	defer prometheus.Unregister(fp.metricRequestsTotal)
 
 	totalRequests := byte(10)
 	reqs := []*httpgrpc.HTTPRequest{}
@@ -50,14 +53,16 @@ func TestRunRequests(t *testing.T) {
 
 	// check that counter metric is working
 	m := &dto.Metric{}
-	err := metricWorkerRequests.Write(m)
+	err := fp.metricRequestsTotal.Write(m)
 	require.NoError(t, err)
 	require.Equal(t, float64(totalRequests), m.Counter.GetValue())
 }
 
 func TestHandleSendError(t *testing.T) {
 	inf := newFrontendProcessor(Config{}, nil, log.NewNopLogger())
 	fp := inf.(*frontendProcessor)
+	// unregister metric in test avoid panic due to registering it twice in tests
+	defer prometheus.Unregister(fp.metricRequestsTotal)
 
 	err := fp.handleSendError(nil)
 	require.NoError(t, err)