Report faulting file when config reload fails (#11304)

* fixed error format to include faulting file,some go lint issues

* changelog updated

* review round 1

* not breaking

CHANGELOG.next.asciidoc

@@ -146,6 +146,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Include ip and boolean type when generating index pattern. {pull}10995[10995]
 - Cancelling enrollment of a beat will not enroll the beat. {issue}10150[10150]
 - Add missing fields and test cases for libbeat add_kubernetes_metadata processor. {issue}11133[11133], {pull}11134[11134]
+- Report faulting file when config reload fails. {pull}[11304]11304
 
 *Auditbeat*
 

libbeat/cfgfile/reload.go

@@ -35,6 +35,7 @@ import (
 )
 
 var (
+	// DefaultDynamicConfig provides default behavior for a Runner.
 	DefaultDynamicConfig = DynamicConfig{
 		Reload: Reload{
 			Period:  10 * time.Second,
@@ -58,16 +59,20 @@ type DynamicConfig struct {
 	Reload Reload `config:"reload"`
 }
 
+// Reload defines reload behavior and frequency
 type Reload struct {
 	Period  time.Duration `config:"period"`
 	Enabled bool          `config:"enabled"`
 }
 
+// RunnerFactory is used for creating of new Runners
 type RunnerFactory interface {
 	Create(p beat.Pipeline, config *common.Config, meta *common.MapStrPointer) (Runner, error)
 	CheckConfig(config *common.Config) error
 }
 
+// Runner is a simple interface providing a simple way to
+// Start and Stop Reloader
 type Runner interface {
 	// We include fmt.Stringer here because we do log debug messages that must print
 	// something for the given Runner. We need Runner implementers to consciously implement a
@@ -220,7 +225,7 @@ func (rl *Reloader) loadConfigs(files []string) ([]*reload.ConfigWithMeta, error
 		configs, err := LoadList(file)
 		if err != nil {
 			errs = append(errs, err)
-			logp.Err("Error loading config: %s", err)
+			logp.Err("Error loading config from file '%s', error %v", file, err)
 			continue
 		}
 

libbeat/template/load.go

@@ -29,13 +29,15 @@ import (
 	"github.com/elastic/beats/libbeat/paths"
 )
 
-// TemplateLoader is a subset of the Elasticsearch client API capable of
+// ESClient is a subset of the Elasticsearch client API capable of
 // loading the template.
 type ESClient interface {
 	Request(method, path string, pipeline string, params map[string]string, body interface{}) (int, []byte, error)
 	GetVersion() common.Version
 }
 
+// Loader is a template loader capable of loading the template using
+// Elasticsearch Client API
 type Loader struct {
 	config    TemplateConfig
 	client    ESClient