Add metrics parsing from config file and report metrics on runner

Metrics will be configured in files and not through the CLI to
avoid unnecessarily expanding the CLI options.

Flush metrics on shutdown and configure dogstatsd reporting interval
Add no-op provider
Add documentation
Add telemetry config tests
Change instruments helper to accept nil meter

README.md

@@ -622,8 +622,32 @@ template {
     min = "2s"
     max = "10s"
   }
-}
 
+  # These are example configurations for monitoring Consul Template metrics.
+  # This block is an HCL mapping to [OpenCensus](https://opencensus.io/) configurations for
+  # various exporters. Telemetry configuration is only supported in
+  # configuration files and not as CLI flags. Only one metric provider can
+  # be used at a given time.
+  telemetry {
+    stdout {
+      reporting_interval = "60s"
+      pretty_print = false
+      do_not_print_time = false
+    }
+
+    dogstatsd {
+      // address describes the destination for exporting dogstatsd data.
+      // e.g., udp://host:port tcp://host:port unix:///socket/path
+      address = "udp://127.0.0.1:8125"
+      reporting_interval = "60s"
+    }
+
+    prometheus {
+      reporting_interval = "60s"
+      port = 8888
+    }
+  }
+}
 ```
 
 Note that not all fields are required. If you are not retrieving secrets from

cli.go

@@ -15,6 +15,7 @@ import (
 	"github.com/hashicorp/consul-template/logging"
 	"github.com/hashicorp/consul-template/manager"
 	"github.com/hashicorp/consul-template/signals"
+	"github.com/hashicorp/consul-template/telemetry"
 	"github.com/hashicorp/consul-template/version"
 )
 
@@ -102,6 +103,13 @@ func (cli *CLI) Run(args []string) int {
 		return ExitCodeOK
 	}
 
+	// Initialize telemetry
+	tel, err := telemetry.Init(config.Telemetry)
+	if err != nil {
+		return logError(err, ExitCodeConfigError)
+	}
+	defer tel.Stop()
+
 	// Initial runner
 	runner, err := manager.NewRunner(config, dry)
 	if err != nil {

config/config.go

@@ -78,6 +78,9 @@ type Config struct {
 	// Syslog is the configuration for syslog.
 	Syslog *SyslogConfig `mapstructure:"syslog"`
 
+	// Telemetry is the configuration for collecting and emitting telemetry.
+	Telemetry *TelemetryConfig `mapstructure:"telemetry"`
+
 	// Templates is the list of templates.
 	Templates *TemplateConfigs `mapstructure:"template"`
 
@@ -135,6 +138,10 @@ func (c *Config) Copy() *Config {
 		o.Syslog = c.Syslog.Copy()
 	}
 
+	if c.Telemetry != nil {
+		o.Telemetry = c.Telemetry.Copy()
+	}
+
 	if c.Templates != nil {
 		o.Templates = c.Templates.Copy()
 	}
@@ -210,6 +217,10 @@ func (c *Config) Merge(o *Config) *Config {
 		r.Syslog = r.Syslog.Merge(o.Syslog)
 	}
 
+	if o.Telemetry != nil {
+		r.Telemetry = r.Telemetry.Merge(o.Telemetry)
+	}
+
 	if o.Templates != nil {
 		r.Templates = r.Templates.Merge(o.Templates)
 	}
@@ -256,6 +267,10 @@ func Parse(s string) (*Config, error) {
 		"exec.env",
 		"ssl",
 		"syslog",
+		"telemetry",
+		"telemetry.stdout",
+		"telemetry.dogstatsd",
+		"telemetry.prometheus",
 		"vault",
 		"vault.retry",
 		"vault.ssl",
@@ -413,6 +428,7 @@ func (c *Config) GoString() string {
 		"PidFile:%s, "+
 		"ReloadSignal:%s, "+
 		"Syslog:%#v, "+
+		"Telemetry:%#v, "+
 		"Templates:%#v, "+
 		"Vault:%#v, "+
 		"Wait:%#v,"+
@@ -429,6 +445,7 @@ func (c *Config) GoString() string {
 		StringGoString(c.PidFile),
 		SignalGoString(c.ReloadSignal),
 		c.Syslog,
+		c.Telemetry.GoString(),
 		c.Templates,
 		c.Vault,
 		c.Wait,
@@ -467,6 +484,7 @@ func DefaultConfig() *Config {
 		DefaultDelims: DefaultDefaultDelims(),
 		Exec:          DefaultExecConfig(),
 		Syslog:        DefaultSyslogConfig(),
+		Telemetry:     DefaultTelemetryConfig(),
 		Templates:     DefaultTemplateConfigs(),
 		Vault:         DefaultVaultConfig(),
 		Wait:          DefaultWaitConfig(),
@@ -529,6 +547,11 @@ func (c *Config) Finalize() {
 	}
 	c.Syslog.Finalize()
 
+	if c.Telemetry == nil {
+		c.Telemetry = DefaultTelemetryConfig()
+	}
+	c.Telemetry.Finalize()
+
 	if c.Templates == nil {
 		c.Templates = DefaultTemplateConfigs()
 	}

config/convert.go

@@ -22,6 +22,15 @@ func BoolVal(b *bool) bool {
 	return *b
 }
 
+// BoolCopy returns a copy of the boolean pointer
+func BoolCopy(b *bool) *bool {
+	if b == nil {
+		return nil
+	}
+
+	return Bool(*b)
+}
+
 // BoolGoString returns the value of the boolean for printing in a string.
 func BoolGoString(b *bool) string {
 	if b == nil {
@@ -53,6 +62,15 @@ func FileModeVal(o *os.FileMode) os.FileMode {
 	return *o
 }
 
+// FileModeCopy returns a copy of the os.FireMode
+func FileModeCopy(o *os.FileMode) *os.FileMode {
+	if o == nil {
+		return nil
+	}
+
+	return FileMode(*o)
+}
+
 // FileModeGoString returns the value of the os.FileMode for printing in a
 // string.
 func FileModeGoString(o *os.FileMode) string {
@@ -85,6 +103,15 @@ func IntVal(i *int) int {
 	return *i
 }
 
+// IntCopy returns a copy of the int pointer
+func IntCopy(i *int) *int {
+	if i == nil {
+		return nil
+	}
+
+	return Int(*i)
+}
+
 // IntGoString returns the value of the int for printing in a string.
 func IntGoString(i *int) string {
 	if i == nil {
@@ -102,6 +129,46 @@ func IntPresent(i *int) bool {
 	return *i != 0
 }
 
+// Uint returns a pointer to the given uint.
+func Uint(i uint) *uint {
+	return &i
+}
+
+// UintVal returns the value of the uint at the pointer, or 0 if the pointer is
+// nil.
+func UintVal(i *uint) uint {
+	if i == nil {
+		return 0
+	}
+	return *i
+}
+
+// UintCopy returns a copy of the uint pointer
+func UintCopy(i *uint) *uint {
+	if i == nil {
+		return nil
+	}
+
+	return Uint(*i)
+}
+
+// UintGoString returns the value of the uint for printing in a string.
+func UintGoString(i *uint) string {
+	if i == nil {
+		return "(*uint)(nil)"
+	}
+	return fmt.Sprintf("%d", *i)
+}
+
+// UintPresent returns a boolean indicating if the pointer is nil, or if the
+// pointer is pointing to the zero value.
+func UintPresent(i *uint) bool {
+	if i == nil {
+		return false
+	}
+	return *i != 0
+}
+
 // Signal returns a pointer to the given os.Signal.
 func Signal(s os.Signal) *os.Signal {
 	return &s
@@ -116,6 +183,15 @@ func SignalVal(s *os.Signal) os.Signal {
 	return *s
 }
 
+// SignalCopy returns a copy of the os.Signal
+func SignalCopy(s *os.Signal) *os.Signal {
+	if s == nil {
+		return nil
+	}
+
+	return Signal(*s)
+}
+
 // SignalGoString returns the value of the os.Signal for printing in a string.
 func SignalGoString(s *os.Signal) string {
 	if s == nil {
@@ -149,6 +225,15 @@ func StringVal(s *string) string {
 	return *s
 }
 
+// StringCopy returns a copy of the string pointer
+func StringCopy(s *string) *string {
+	if s == nil {
+		return nil
+	}
+
+	return String(*s)
+}
+
 // StringGoString returns the value of the string for printing in a string.
 func StringGoString(s *string) string {
 	if s == nil {
@@ -179,6 +264,15 @@ func TimeDurationVal(t *time.Duration) time.Duration {
 	return *t
 }
 
+// TimeDurationCopy returns a copy of the time.Duration pointer
+func TimeDurationCopy(t *time.Duration) *time.Duration {
+	if t == nil {
+		return nil
+	}
+
+	return TimeDuration(*t)
+}
+
 // TimeDurationGoString returns the value of the time.Duration for printing in a
 // string.
 func TimeDurationGoString(t *time.Duration) string {