Disable lockfile under fleet mode (#33988)

* diable lockfile under fleet mode

* update docs

* add changelog

CHANGELOG.next.asciidoc

@@ -45,6 +45,7 @@ https://github.com/elastic/beats/compare/v8.2.0\...main[Check the HEAD diff]
 - Fix Windows service install/uninstall when Win32_Service returns error, add logic to wait until the Windows Service is stopped before proceeding. {pull}33322[33322]
 - Support for multiline zookeeper logs {issue}2496[2496]
 - Allow `clock_nanosleep` in the default seccomp profiles for amd64 and 386. Newer versions of glibc (e.g. 2.31) require it. {issue}33792[33792]
+- Disable lockfile when running under elastic-agent. {pull}33988[33988]
 
 *Auditbeat*
 

libbeat/cmd/instance/beat.go

@@ -46,6 +46,7 @@ import (
 	"github.com/elastic/beats/v7/libbeat/cloudid"
 	"github.com/elastic/beats/v7/libbeat/cmd/instance/locks"
 	"github.com/elastic/beats/v7/libbeat/common"
+	"github.com/elastic/beats/v7/libbeat/common/fleetmode"
 	"github.com/elastic/beats/v7/libbeat/common/reload"
 	"github.com/elastic/beats/v7/libbeat/common/seccomp"
 	"github.com/elastic/beats/v7/libbeat/dashboards"
@@ -386,15 +387,19 @@ func (b *Beat) launch(settings Settings, bt beat.Creator) error {
 	defer svc.NotifyTermination()
 
 	// Try to acquire exclusive lock on data path to prevent another beat instance
-	// sharing same data path.
-	bl := locks.New(b.Info)
-	err := bl.Lock()
-	if err != nil {
-		return err
+	// sharing same data path. This is disabled under elastic-agent.
+	if !fleetmode.Enabled() {
+		bl := locks.New(b.Info)
+		err := bl.Lock()
+		if err != nil {
+			return err
+		}
+		defer func() {
+			_ = bl.Unlock()
+		}()
+	} else {
+		logp.Info("running under elastic-agent, per-beat lockfiles disabled")
 	}
-	defer func() {
-		_ = bl.Unlock()
-	}()
 
 	svc.BeforeRun()
 	defer svc.Cleanup()
@@ -405,6 +410,7 @@ func (b *Beat) launch(settings Settings, bt beat.Creator) error {
 	// set the appropriate permission on the unix domain file without having to whitelist anything
 	// that would be set at runtime.
 	if b.Config.HTTP.Enabled() {
+		var err error
 		b.API, err = api.NewWithDefaultRoutes(logp.NewLogger(""), b.Config.HTTP, monitoring.GetNamespace)
 		if err != nil {
 			return fmt.Errorf("could not start the HTTP server for the API: %w", err)
@@ -422,7 +428,7 @@ func (b *Beat) launch(settings Settings, bt beat.Creator) error {
 		}
 	}
 
-	if err = seccomp.LoadFilter(b.Config.Seccomp); err != nil {
+	if err := seccomp.LoadFilter(b.Config.Seccomp); err != nil {
 		return err
 	}