Support default config paths

precedence will be:

 1. --config command-line option
 2. $TELEGRAF_CONFIG_PATH
 3. $HOME/.telegraf/telegraf.conf
 4. /etc/telegraf/telegraf.conf

CHANGELOG.md

@@ -47,7 +47,7 @@ based on _prefix_ in addition to globs. This means that a filter like
   - cassandra: `host -> cassandra_host`
   - disque: `host -> disque_host`
   - rethinkdb: `host -> rethinkdb_host`
-  
+
 - **Breaking Change**: The `win_perf_counters` input has been changed to sanitize field names, replacing `/Sec` and `/sec` with `_persec`, as well as spaces with underscores. This is needed because Graphite doesn't like slashes and spaces, and was failing to accept metrics that had them. The `/[sS]ec` -> `_persec` is just to make things clearer and uniform.
 
 ### Features
@@ -67,7 +67,8 @@ based on _prefix_ in addition to globs. This means that a filter like
 - [#967](https://github.com/influxdata/telegraf/issues/967): Buffer logging improvements.
 - [#1107](https://github.com/influxdata/telegraf/issues/1107): Support lustre2 job stats. Thanks @hanleyja!
 - [#1110](https://github.com/influxdata/telegraf/pull/1110): Sanitize * to - in graphite serializer. Thanks @goodeggs!
-- [#1118] (https://github.com/influxdata/telegraf/pull/1118): Sanitize Counter names for `win_perf_counters` input.
+- [#1118](https://github.com/influxdata/telegraf/pull/1118): Sanitize Counter names for `win_perf_counters` input.
+- [#1122](https://github.com/influxdata/telegraf/pull/1122): Support setting config path through env variable and default paths.
 
 ### Bugfixes
 

cmd/telegraf/telegraf.go

@@ -71,6 +71,13 @@ The flags are:
   -quiet             run in quiet mode
   -version           print the version to stdout
 
+In addition to the -config flag, telegraf will also load the config file from
+an environment variable or default location. Precedence is:
+  1. -config flag
+  2. $TELEGRAF_CONFIG_PATH environment variable
+  3. $HOME/.telegraf/telegraf.conf
+  4. /etc/telegraf/telegraf.conf
+
 Examples:
 
   # generate a telegraf config file:
@@ -98,12 +105,10 @@ func main() {
 		flag.Parse()
 		args := flag.Args()
 
-		if flag.NFlag() == 0 && len(args) == 0 {
-			usageExit(0)
-		}
-
 		var inputFilters []string
 		if *fInputFiltersLegacy != "" {
+			fmt.Printf("WARNING '--filter' flag is deprecated, please use" +
+				" '--input-filter'")
 			inputFilter := strings.TrimSpace(*fInputFiltersLegacy)
 			inputFilters = strings.Split(":"+inputFilter+":", ":")
 		}
@@ -114,6 +119,8 @@ func main() {
 
 		var outputFilters []string
 		if *fOutputFiltersLegacy != "" {
+			fmt.Printf("WARNING '--outputfilter' flag is deprecated, please use" +
+				" '--output-filter'")
 			outputFilter := strings.TrimSpace(*fOutputFiltersLegacy)
 			outputFilters = strings.Split(":"+outputFilter+":", ":")
 		}
@@ -170,25 +177,19 @@ func main() {
 			return
 		}
 
-		var (
-			c   *config.Config
-			err error
-		)
-
-		if *fConfig != "" {
-			c = config.NewConfig()
-			c.OutputFilters = outputFilters
-			c.InputFilters = inputFilters
-			err = c.LoadConfig(*fConfig)
-			if err != nil {
-				log.Fatal(err)
-			}
-		} else {
-			fmt.Println("You must specify a config file. See telegraf --help")
+		// If no other options are specified, load the config file and run.
+		c := config.NewConfig()
+		c.OutputFilters = outputFilters
+		c.InputFilters = inputFilters
+		err := c.LoadConfig(*fConfig)
+		if err != nil {
+			fmt.Println(err)
 			os.Exit(1)
 		}
 
 		if *fConfigDirectoryLegacy != "" {
+			fmt.Printf("WARNING '--configdirectory' flag is deprecated, please use" +
+				" '--config-directory'")
 			err = c.LoadDirectory(*fConfigDirectoryLegacy)
 			if err != nil {
 				log.Fatal(err)

docs/CONFIGURATION.md

@@ -15,8 +15,8 @@ To generate a file with specific inputs and outputs, you can use the
 telegraf -sample-config -input-filter cpu:mem:net:swap -output-filter influxdb:kafka
 ```
 
-You can see the latest config file with all available plugins
-[here](https://github.com/influxdata/telegraf/blob/master/etc/telegraf.conf)
+You can see the latest config file with all available plugins here:
+[telegraf.conf](https://github.com/influxdata/telegraf/blob/master/etc/telegraf.conf)
 
 ## Environment Variables
 
@@ -79,7 +79,7 @@ match against the tag name, and if it matches the measurement is emitted.
 * **tagdrop**: The inverse of tagpass. If a tag matches, the measurement is not
 emitted. This is tested on measurements that have passed the tagpass test.
 * **tagexclude**: tagexclude can be used to exclude a tag from measurement(s).
-As opposed to tagdrop, which will drop an entire measurement based on it's 
+As opposed to tagdrop, which will drop an entire measurement based on it's
 tags, tagexclude simply strips the given tag keys from the measurement. This
 can be used on inputs & outputs, but it is _recommended_ to be used on inputs,
 as it is more efficient to filter out tags at the ingestion point.

internal/config/config.go

@@ -412,8 +412,35 @@ func (c *Config) LoadDirectory(path string) error {
 	return nil
 }
 
+// Try to find a default config file at these locations (in order):
+//   1. $TELEGRAF_CONFIG_PATH
+//   2. $HOME/.telegraf/telegraf.conf
+//   3. /etc/telegraf/telegraf.conf
+//
+func getDefaultConfigPath() (string, error) {
+	envfile := os.Getenv("TELEGRAF_CONFIG_PATH")
+	homefile := os.ExpandEnv("${HOME}/.telegraf/telegraf.conf")
+	etcfile := "/etc/telegraf/telegraf.conf"
+	for _, path := range []string{envfile, homefile, etcfile} {
+		if _, err := os.Stat(path); err == nil {
+			log.Printf("Using config file: %s", path)
+			return path, 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)
+}
+
 // LoadConfig loads the given config file and applies it to c
 func (c *Config) LoadConfig(path string) error {
+	var err error
+	if path == "" {
+		if path, err = getDefaultConfigPath(); err != nil {
+			return err
+		}
+	}
 	tbl, err := parseFile(path)
 	if err != nil {
 		return fmt.Errorf("Error parsing %s, %s", path, err)