feat(agent): add /etc/telegraf/telegraf.d to default config locations

This will add /etc/telegraf/telegraf.d to the list of default
configuration locations to load from. Currently, users need to specify
an empty /etc/telegraf/telegraf.conf file and specify they want to
include the configuraiton directory outside of the RPM and DEB.

A common use case is for Docker where users want to upload an entire
directory of configurations and run telegraf. Right now they have to add
a custom launch command, when in reality we should include this
directory by default.

This also means that the --config option can be omitted from the CLI
if a user is only using --config-directory.

fixes: #5656
fixes: #5571

cmd/telegraf/telegraf.go

@@ -208,13 +208,8 @@ func (t *Telegraf) loadConfiguration() (*config.Config, error) {
 	c.SecretStoreFilters = t.secretstoreFilters
 
 	var configFiles []string
-	// providing no "config" flag should load default config
-	if len(t.config) == 0 {
-		configFiles = append(configFiles, "")
-	} else {
-		configFiles = append(configFiles, t.config...)
-	}
 
+	configFiles = append(configFiles, t.config...)
 	for _, fConfigDirectory := range t.configDir {
 		files, err := config.WalkDirectory(fConfigDirectory)
 		if err != nil {
@@ -223,6 +218,12 @@ func (t *Telegraf) loadConfiguration() (*config.Config, error) {
 		configFiles = append(configFiles, files...)
 	}
 
+	// providing no "config" or "config-directory" flag(s) should load default
+	// configuration files
+	if len(configFiles) == 0 {
+		configFiles = append(configFiles, "")
+	}
+
 	t.configFiles = configFiles
 	if err := c.LoadAll(configFiles...); err != nil {
 		return c, err

config/config.go

@@ -362,32 +362,57 @@ func WalkDirectory(path string) ([]string, error) {
 // Try to find a default config file at these locations (in order):
 //  1. $TELEGRAF_CONFIG_PATH
 //  2. $HOME/.telegraf/telegraf.conf
-//  3. /etc/telegraf/telegraf.conf
-func getDefaultConfigPath() (string, error) {
+//  3. /etc/telegraf/telegraf.conf and /etc/telegraf/telegraf.d/*.conf
+func getDefaultConfigPath() ([]string, error) {
 	envfile := os.Getenv("TELEGRAF_CONFIG_PATH")
 	homefile := os.ExpandEnv("${HOME}/.telegraf/telegraf.conf")
 	etcfile := "/etc/telegraf/telegraf.conf"
+	etcfolder := "/etc/telegraf/telegraf.conf.d"
+
 	if runtime.GOOS == "windows" {
 		programFiles := os.Getenv("ProgramFiles")
 		if programFiles == "" { // Should never happen
 			programFiles = `C:\Program Files`
 		}
 		etcfile = programFiles + `\Telegraf\telegraf.conf`
+		etcfolder = programFiles + `\Telegraf\telegraf.conf.d\`
 	}
-	for _, path := range []string{envfile, homefile, etcfile} {
+
+	for _, path := range []string{envfile, homefile} {
 		if isURL(path) {
 			log.Printf("I! Using config url: %s", path)
-			return path, nil
+			return []string{path}, nil
 		}
 		if _, err := os.Stat(path); err == nil {
 			log.Printf("I! Using config file: %s", path)
-			return path, nil
+			return []string{path}, nil
 		}
 	}
 
+	// At this point we need to check if the files under /etc/telegraf are
+	// populated and return them all.
+	confFiles := []string{}
+	if _, err := os.Stat(etcfile); err == nil {
+		log.Printf("I! Using config file: %s", etcfile)
+		confFiles = append(confFiles, etcfile)
+	}
+	if _, err := os.Stat(etcfolder); err == nil {
+		files, err := WalkDirectory(etcfolder)
+		if err != nil {
+			log.Printf("W! unable walk '%s': %s", etcfolder, err)
+		}
+		for _, file := range files {
+			log.Printf("I! Using config file: %s", file)
+		}
+		confFiles = append(confFiles, files...)
+	}
+	if len(confFiles) > 0 {
+		return confFiles, nil
+	}
+
 	// if we got here, we didn't find a file in a default location
-	return "", fmt.Errorf("no config file specified, and could not find one"+
-		" in $TELEGRAF_CONFIG_PATH, %s, or %s", homefile, etcfile)
+	return nil, fmt.Errorf("no config file specified, and could not find one"+
+		" in $TELEGRAF_CONFIG_PATH, %s, %s, or %s/*.conf", homefile, etcfile, etcfolder)
 }
 
 // isURL checks if string is valid url
@@ -396,22 +421,30 @@ func isURL(str string) bool {
 	return err == nil && u.Scheme != "" && u.Host != ""
 }
 
-// LoadConfig loads the given config file and applies it to c
+// LoadConfig loads the given config files and applies it to c
 func (c *Config) LoadConfig(path string) error {
 	var err error
+	paths := []string{}
+
 	if path == "" {
-		if path, err = getDefaultConfigPath(); err != nil {
+		if paths, err = getDefaultConfigPath(); err != nil {
 			return err
 		}
-	}
-	data, err := LoadConfigFile(path)
-	if err != nil {
-		return fmt.Errorf("error loading config file %s: %w", path, err)
+	} else {
+		paths = append(paths, path)
 	}
 
-	if err = c.LoadConfigData(data); err != nil {
-		return fmt.Errorf("error loading config file %s: %w", path, err)
+	for _, path := range paths {
+		data, err := LoadConfigFile(path)
+		if err != nil {
+			return fmt.Errorf("error loading config file %s: %w", path, err)
+		}
+
+		if err = c.LoadConfigData(data); err != nil {
+			return fmt.Errorf("error loading config file %s: %w", path, err)
+		}
 	}
+
 	return nil
 }
 

config/config_test.go

@@ -484,7 +484,7 @@ func TestConfig_getDefaultConfigPathFromEnvURL(t *testing.T) {
 	require.NoError(t, err)
 	configPath, err := getDefaultConfigPath()
 	require.NoError(t, err)
-	require.Equal(t, ts.URL, configPath)
+	require.Equal(t, []string{ts.URL}, configPath)
 	err = c.LoadConfig("")
 	require.NoError(t, err)
 }