Add new Prom metrics fn_timeout and fn_errors (#679)

* Add new Prom metric fn_timedout

* Add new Prometheus metric fn_errors

* Tidy up variable name

* Add new Prometheus metric fn_errors

* gofmt

api/agent/stats.go

@@ -94,7 +94,7 @@ func (s *stats) DequeueAndStart(ctx context.Context, app string, path string) {
 
 	s.running++
 	s.getStatsForFunction(path).running++
-	common.IncrementGauge(ctx, runningSuffix)
+	common.IncrementGauge(ctx, runningMetricName)
 
 	s.mu.Unlock()
 }
@@ -104,7 +104,7 @@ func (s *stats) Complete(ctx context.Context, app string, path string) {
 
 	s.running--
 	s.getStatsForFunction(path).running--
-	common.DecrementGauge(ctx, runningSuffix)
+	common.DecrementGauge(ctx, runningMetricName)
 
 	s.complete++
 	s.getStatsForFunction(path).complete++
@@ -118,7 +118,7 @@ func (s *stats) Failed(ctx context.Context, app string, path string) {
 
 	s.running--
 	s.getStatsForFunction(path).running--
-	common.DecrementGauge(ctx, runningSuffix)
+	common.DecrementGauge(ctx, runningMetricName)
 
 	s.failed++
 	s.getStatsForFunction(path).failed++
@@ -141,6 +141,14 @@ func (s *stats) DequeueAndFail(ctx context.Context, app string, path string) {
 	s.mu.Unlock()
 }
 
+func (s *stats) IncrementTimedout(ctx context.Context) {
+	common.IncrementCounter(ctx, timedoutMetricName)
+}
+
+func (s *stats) IncrementErrors(ctx context.Context) {
+	common.IncrementCounter(ctx, errorsMetricName)
+}
+
 func (s *stats) Stats() Stats {
 	var stats Stats
 	s.mu.Lock()
@@ -160,7 +168,9 @@ func (s *stats) Stats() Stats {
 const (
 	queuedMetricName    = "queued"
 	callsMetricName     = "calls"
-	runningSuffix       = "running"
+	runningMetricName   = "running"
 	completedMetricName = "completed"
 	failedMetricName    = "failed"
+	timedoutMetricName  = "timedout"
+	errorsMetricName    = "errors"
 )