Cherry-pick #8449 to 6.x: Allow to pass config overrides via the Settings Struct

CHANGELOG-developer.asciidoc

@@ -49,3 +49,4 @@ The list below covers the major changes between 6.3.0 and master only.
 - Libbeat provides a new function `cmd.GenRootCmdWithSettings` that should be preferred over deprecated functions
   `cmd.GenRootCmd`, `cmd.GenRootCmdWithRunFlags`, and `cmd.GenRootCmdWithIndexPrefixWithRunFlags`. {pull}7850[7850]
 - Set current year in generator templates. {pull}8396[8396]
+- You can now override default settings of libbeat by using instance.Settings. {pull}8449[8449]

libbeat/cfgfile/cfgfile.go

@@ -37,7 +37,7 @@ var (
 	testConfig  = flag.Bool("configtest", false, "Test configuration and exit.")
 
 	// Additional default settings, that must be available for variable expansion
-	defaults = mustNewConfigFrom(map[string]interface{}{
+	defaults = common.MustNewConfigFrom(map[string]interface{}{
 		"path": map[string]interface{}{
 			"home":   ".", // to be initialized by beat
 			"config": "${path.home}",
@@ -63,14 +63,6 @@ func init() {
 	makePathFlag("path.logs", "Logs path")
 }
 
-func mustNewConfigFrom(from interface{}) *common.Config {
-	cfg, err := common.NewConfigFrom(from)
-	if err != nil {
-		panic(err)
-	}
-	return cfg
-}
-
 // ChangeDefaultCfgfileFlag replaces the value and default value for the `-c`
 // flag so that it reflects the beat name.
 func ChangeDefaultCfgfileFlag(beatName string) error {
@@ -105,7 +97,7 @@ func HandleFlags() error {
 // structure. If path is empty this method reads from the configuration
 // file specified by the '-c' command line flag.
 func Read(out interface{}, path string) error {
-	config, err := Load(path)
+	config, err := Load(path, nil)
 	if err != nil {
 		return err
 	}
@@ -116,7 +108,7 @@ func Read(out interface{}, path string) error {
 // Load reads the configuration from a YAML file structure. If path is empty
 // this method reads from the configuration file specified by the '-c' command
 // line flag.
-func Load(path string) (*common.Config, error) {
+func Load(path string, beatOverrides *common.Config) (*common.Config, error) {
 	var config *common.Config
 	var err error
 
@@ -142,13 +134,22 @@ func Load(path string) (*common.Config, error) {
 		return nil, err
 	}
 
-	config, err = common.MergeConfigs(
-		defaults,
-		config,
-		overwrites,
-	)
-	if err != nil {
-		return nil, err
+	if beatOverrides != nil {
+		config, err = common.MergeConfigs(
+			defaults,
+			beatOverrides,
+			config,
+			overwrites,
+		)
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		config, err = common.MergeConfigs(
+			defaults,
+			config,
+			overwrites,
+		)
 	}
 
 	config.PrintDebugf("Complete configuration loaded:")

libbeat/cmd/instance/beat.go

@@ -228,8 +228,8 @@ func NewBeat(name, indexPrefix, v string) (*Beat, error) {
 	return &Beat{Beat: b}, nil
 }
 
-// init does initialization of things common to all actions (read confs, flags)
-func (b *Beat) Init() error {
+// InitWithSettings does initialization of things common to all actions (read confs, flags)
+func (b *Beat) InitWithSettings(settings Settings) error {
 	err := b.handleFlags()
 	if err != nil {
 		return err
@@ -239,13 +239,20 @@ func (b *Beat) Init() error {
 		return err
 	}
 
-	if err := b.configure(); err != nil {
+	if err := b.configure(settings); err != nil {
 		return err
 	}
 
 	return nil
 }
 
+// Init does initialization of things common to all actions (read confs, flags)
+//
+// Deprecated: use InitWithSettings
+func (b *Beat) Init() error {
+	return b.InitWithSettings(Settings{})
+}
+
 // BeatConfig returns config section for this beat
 func (b *Beat) BeatConfig() (*common.Config, error) {
 	configName := strings.ToLower(b.Info.Beat)
@@ -315,7 +322,7 @@ func (b *Beat) launch(settings Settings, bt beat.Creator) error {
 	defer logp.Sync()
 	defer logp.Info("%s stopped.", b.Info.Beat)
 
-	err := b.Init()
+	err := b.InitWithSettings(settings)
 	if err != nil {
 		return err
 	}
@@ -496,10 +503,10 @@ func (b *Beat) handleFlags() error {
 // config reads the configuration file from disk, parses the common options
 // defined in BeatConfig, initializes logging, and set GOMAXPROCS if defined
 // in the config. Lastly it invokes the Config method implemented by the beat.
-func (b *Beat) configure() error {
+func (b *Beat) configure(settings Settings) error {
 	var err error
 
-	cfg, err := cfgfile.Load("")
+	cfg, err := cfgfile.Load("", settings.ConfigOverrides)
 	if err != nil {
 		return fmt.Errorf("error loading config file: %v", err)
 	}

libbeat/cmd/instance/settings.go

@@ -20,14 +20,16 @@ package instance
 import (
 	"github.com/spf13/pflag"
 
+	"github.com/elastic/beats/libbeat/common"
 	"github.com/elastic/beats/libbeat/monitoring/report"
 )
 
 // Settings contains basic settings for any beat to pass into GenRootCmd
 type Settings struct {
-	Name        string
-	IndexPrefix string
-	Version     string
-	Monitoring  report.Settings
-	RunFlags    *pflag.FlagSet
+	Name            string
+	IndexPrefix     string
+	Version         string
+	Monitoring      report.Settings
+	RunFlags        *pflag.FlagSet
+	ConfigOverrides *common.Config
 }