add option to disable dns lookup for chronyc

closes #1265

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

@@ -20,7 +20,8 @@ var (
 )
 
 type Chrony struct {
-	path string
+	DNSLookup bool `toml:"dns_lookup"`
+	path      string
 }
 
 func (*Chrony) Description() 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))

plugins/inputs/chrony/chrony_test.go

@@ -42,6 +42,15 @@ func TestGather(t *testing.T) {
 	}
 
 	acc.AssertContainsTaggedFields(t, "chrony", fields, tags)
+
+	// test with dns lookup
+	c.DNSLookup = true
+	err = c.Gather(&acc)
+	if err != nil {
+		t.Fatal(err)
+	}
+	acc.AssertContainsTaggedFields(t, "chrony", fields, tags)
+
 }
 
 // fackeExecCommand is a helper function that mock
@@ -63,8 +72,9 @@ func TestHelperProcess(t *testing.T) {
 		return
 	}
 
-	mockData := `Reference ID    : 192.168.1.22 (ntp.example.com)
-Stratum         : 3
+	lookup := "Reference ID    : 192.168.1.22 (ntp.example.com)\n"
+	noLookup := "Reference ID    : 192.168.1.22 (192.168.1.22)\n"
+	mockData := `Stratum         : 3
 Ref time (UTC)  : Thu May 12 14:27:07 2016
 System time     : 0.000020390 seconds fast of NTP time
 Last offset     : +0.000012651 seconds
@@ -84,8 +94,12 @@ Leap status     : Normal
 	// /tmp/go-build970079519/…/_test/integration.test -test.run=TestHelperProcess --
 	cmd, args := args[3], args[4:]
 
-	if cmd == "chronyc" && args[0] == "tracking" {
-		fmt.Fprint(os.Stdout, mockData)
+	if cmd == "chronyc" {
+		if args[0] == "tracking" {
+			fmt.Fprint(os.Stdout, lookup+mockData)
+		} else {
+			fmt.Fprint(os.Stdout, noLookup+mockData)
+		}
 	} else {
 		fmt.Fprint(os.Stdout, "command not found")
 		os.Exit(1)