Add Signal Name to Signal Metrics (cadence-workflow#4161)

What changed?
Adding signalName as a tag to the signal metrics. This will help filtering signal metrics by signal name and create alerts.

See https://t3.uberinternal.com/browse/CDNC-1232 for more details.

Why?
With this change customers can create alerts per signal name and monitor abnormalities.

common/metrics/tags.go

@@ -43,6 +43,7 @@ const (
 	invariantType  = "invariantType"
 	kafkaPartition = "kafkaPartition"
 	transport      = "transport"
+	signalName     = "signalName"
 
 	domainAllValue = "all"
 	unknownValue   = "_unknown_"
@@ -153,3 +154,8 @@ func ThriftTransportTag() Tag {
 func GPRCTransportTag() Tag {
 	return simpleMetric{key: transport, value: transportGRPC}
 }
+
+// SignalNameTag returns a new SignalName tag
+func SignalNameTag(value string) Tag {
+	return metricWithUnknown(signalName, value)
+}

service/frontend/workflowHandler.go

@@ -2108,6 +2108,10 @@ func (wh *WorkflowHandler) GetWorkflowExecutionHistory(
 	}, nil
 }
 
+func withSignalName(ctx context.Context, signalName string) context.Context {
+	return metrics.TagContext(ctx, metrics.SignalNameTag(signalName))
+}
+
 // SignalWorkflowExecution is used to send a signal event to running workflow execution.  This results in
 // WorkflowExecutionSignaled event recorded in the history and a decision task being created for the execution.
 func (wh *WorkflowHandler) SignalWorkflowExecution(
@@ -2116,6 +2120,7 @@ func (wh *WorkflowHandler) SignalWorkflowExecution(
 ) (retError error) {
 	defer log.CapturePanic(wh.GetLogger(), &retError)
 
+	ctx = withSignalName(ctx, signalRequest.GetSignalName())
 	scope, sw := wh.startRequestProfileWithDomain(ctx, metrics.FrontendSignalWorkflowExecutionScope, signalRequest)
 	defer sw.Stop()
 

service/frontend/workflowHandler_test.go

@@ -1425,6 +1425,33 @@ func (s *workflowHandlerSuite) TestContextMetricsTags() {
 	s.Fail("counter not found")
 }
 
+func (s *workflowHandlerSuite) TestSignalMetricHasSignalName() {
+	wh := s.getWorkflowHandler(s.newConfig(dc.NewInMemoryClient()))
+
+	signalRequest := &types.SignalWorkflowExecutionRequest{
+		SignalName: "test_signal",
+	}
+	wh.SignalWorkflowExecution(context.Background(), signalRequest)
+
+	expectedMetrics := make(map[string]bool)
+	expectedMetrics["test.cadence_requests"] = false
+	expectedMetrics["test.cadence_errors_bad_request"] = false
+
+	snapshot := s.mockResource.MetricsScope.Snapshot()
+	for _, counter := range snapshot.Counters() {
+		if _, ok := expectedMetrics[counter.Name()]; ok {
+			expectedMetrics[counter.Name()] = true
+		}
+		if val, ok := counter.Tags()["signalName"]; ok {
+			s.Equal(val, "test_signal")
+		} else {
+			s.Fail("Couldn't find signalName tag")
+		}
+	}
+	s.True(expectedMetrics["test.cadence_requests"])
+	s.True(expectedMetrics["test.cadence_errors_bad_request"])
+}
+
 func (s *workflowHandlerSuite) newConfig(dynamicClient dc.Client) *Config {
 	return NewConfig(
 		dc.NewCollection(