Fix unused libbeat.config.module metrics (elastic#19168)

These metrics existed in the code but were unused and hence always 0.

"libbeat":{"config":{"module":{"running":0,"starts":0,"stops":0}

I updated the module reload code to increment and set the metrics when changes are applied.

CHANGELOG.next.asciidoc

@@ -134,6 +134,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - The `monitoring.elasticsearch.api_key` value is correctly base64-encoded before being sent to the monitoring Elasticsearch cluster. {issue}18939[18939] {pull}18945[18945]
 - Fix kafka topic setting not allowing upper case characters. {pull}18854[18854] {issue}18640[18640]
 - Fix redis key setting not allowing upper case characters. {pull}18854[18854] {issue}18640[18640]
+- Fix config reload metrics (`libbeat.config.module.start/stops/running`). {pull}19168[19168]
 - Fix metrics hints builder to avoid wrong container metadata usage when port is not exposed {pull}18979[18979]
 
 *Auditbeat*

libbeat/cfgfile/list.go

@@ -85,6 +85,7 @@ func (r *RunnerList) Reload(configs []*reload.ConfigWithMeta) error {
 		r.logger.Debugf("Stopping runner: %s", runner)
 		delete(r.runners, hash)
 		go runner.Stop()
+		moduleStops.Add(1)
 	}
 
 	// Start new runners
@@ -99,8 +100,15 @@ func (r *RunnerList) Reload(configs []*reload.ConfigWithMeta) error {
 		r.logger.Debugf("Starting runner: %s", runner)
 		r.runners[hash] = runner
 		runner.Start()
+		moduleStarts.Add(1)
 	}
 
+	// NOTE: This metric tracks the number of modules in the list. The true
+	// number of modules in the running state may differ because modules can
+	// stop on their own (i.e. on errors) and also when this stops a module
+	// above it is done asynchronously.
+	moduleRunning.Set(int64(len(r.runners)))
+
 	return errs.Err()
 }
 

libbeat/cfgfile/reload.go

@@ -52,7 +52,7 @@ var (
 	configReloads = monitoring.NewInt(nil, "libbeat.config.reloads")
 	moduleStarts  = monitoring.NewInt(nil, "libbeat.config.module.starts")
 	moduleStops   = monitoring.NewInt(nil, "libbeat.config.module.stops")
-	moduleRunning = monitoring.NewInt(nil, "libbeat.config.module.running")
+	moduleRunning = monitoring.NewInt(nil, "libbeat.config.module.running") // Number of modules in the runner list (not necessarily in the running state).
 )
 
 // DynamicConfig loads config files from a given path, allowing to reload new changes