add option to disable dns lookup for chronyc

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Features
 
 - [#1247](https://github.com/influxdata/telegraf/pull/1247): rollbar input plugin. Thanks @francois2metz and @cduez!
+- [#1265](https://github.com/influxdata/telegraf/pull/1265): Make dns lookups for chrony configurable. Thanks @zbindenren!
 
 ### Bugfixes
 

plugins/inputs/chrony/README.md

@@ -40,7 +40,7 @@ is computed for the new frequency, with weights depending on these accuracies. I
 measurements from the reference source follow a consistent trend, the residual will be
 driven to zero over time.
 - Skew - This is the estimated error bound on the frequency.
-- Root delay -This is the total of the network path delays to the stratum-1 computer
+- Root delay - This is the total of the network path delays to the stratum-1 computer
 from which the computer is ultimately synchronised. In certain extreme situations, this
 value can be negative. (This can arise in a symmetric peer arrangement where the computers’
 frequencies are not tracking each other and the network delay is very short relative to the
@@ -56,7 +56,8 @@ Delete second or Not synchronised.
 ```toml
 # Get standard chrony metrics, requires chronyc executable.
 [[inputs.chrony]]
-  # no configuration
+  ## If true, chronyc tries to perform a DNS lookup for the time server.
+  # dns_lookup = false
 ```
 
 ### Measurements & Fields:

plugins/inputs/chrony/chrony.go

@@ -20,6 +20,7 @@ var (
 )
 
 type Chrony struct {
+	DNSLookup bool `toml:"dns_lookup"`
 	path      string
 }
 
@@ -28,14 +29,24 @@ func (*Chrony) Description() string {
 }
 
 func (*Chrony) SampleConfig() string {
-	return ""
+	return `
+  ## If true, chronyc tries to perform a DNS lookup for the time server.
+  # dns_lookup = false
+  `
 }
 
 func (c *Chrony) Gather(acc telegraf.Accumulator) error {
 	if len(c.path) == 0 {
 		return errors.New("chronyc not found: verify that chrony is installed and that chronyc is in your PATH")
 	}
-	cmd := execCommand(c.path, "tracking")
+
+	flags := []string{}
+	if !c.DNSLookup {
+		flags = append(flags, "-n")
+	}
+	flags = append(flags, "tracking")
+
+	cmd := execCommand(c.path, flags...)
 	out, err := internal.CombinedOutputTimeout(cmd, time.Second*5)
 	if err != nil {
 		return fmt.Errorf("failed to run command %s: %s - %s", strings.Join(cmd.Args, " "), err, string(out))