Commit registry writes to stable storage to avoid corrupt registry fi…

…les (#6877) (#7019)

* fsync contents of registry file to storage

(cherry picked from commit 4d2150d)

CHANGELOG.asciidoc

@@ -66,6 +66,7 @@ https://github.com/elastic/beats/compare/v6.0.0-beta2...master[Check the HEAD di
 - Fix panic when log prospector configuration fails to load. {issue}6800[6800]
 - Fix memory leak in log prospector when files cannot be read. {issue}6797[6797]
 - Add raw JSON to message field when JSON parsing fails. {issue}6516[6516]
+- Commit registry writes to stable storage to avoid corrupt registry files. {pull}6877[6877]
 
 *Heartbeat*
 - Fix race due to updates of shared a map, that was not supposed to be shared between multiple go-routines. {issue}6616[6616]

filebeat/registrar/registrar.go

@@ -280,6 +280,8 @@ func (r *Registrar) writeRegistry() error {
 		return err
 	}
 
+	// Commit the changes to storage to avoid corrupt registry files
+	f.Sync()
 	// Directly close file because of windows
 	f.Close()