Implements metrics using armon/go-metrics library

.golangci.yml

@@ -63,6 +63,7 @@ linters-settings:
         # List of allowed packages.
         allow:
           - $gostd
+          - github.com/armon/go-metrics
           - github.com/BurntSushi/toml
           - github.com/Masterminds/sprig/v3
           - github.com/davecgh/go-spew/spew
@@ -84,10 +85,11 @@ linters-settings:
           - github.com/mitchellh/hashstructure
           - github.com/mitchellh/mapstructure
           - github.com/pkg/errors
+          - github.com/prometheus/client_golang/prometheus
           - github.com/stretchr/testify/assert
           - github.com/stretchr/testify/require
           - github.com/coreos/go-systemd
 
 run:
   timeout: 10m
-  concurrency: 4
+  concurrency: 4

README.md

@@ -55,6 +55,7 @@ this functionality might prove useful.
   - [Multiple Commands](#multiple-commands)
 - [Multi-phase Execution](#multi-phase-execution)
 - [Debugging](#debugging)
+- [Telemetry](#telemetry)
 - [FAQ](#faq)
 - [Contributing](#contributing)
 
@@ -407,6 +408,71 @@ $ consul-template -log-level debug ...
 # ...
 ```
 
+## Telemetry
+
+Consul Template uses the [armon/go-metrics](https://github.com/armon/go-metrics) library to implement the Consul Template metrics system. It currently supports metrics exported to circonus API, statsd server, statsite server, dogstatsd server, and prometheus endpoint.
+
+### Key Metrics
+
+These metrics offer insight into Consul Template and capture subprocess activities. The number of dependencies are aggregated from the configured templates, and metrics are collected around a dependency when it is updated from source. This is useful to correlate any upstream changes to downstream actions originating from Consul Template.
+
+Metrics are monitored around template rendering and execution of template commands. These
+metrics indicate the rendering status of a template and how long commands for a template takes
+to provide insight on performance of the templates.
+
+| Metric Name | Labels | Description |
+|-|:-:|-|
+| `consul-template.dependencies_received` | type=(consul\|vault\|local), id=dependencyString | A counter of dependencies received from monitoring value changes |
+| `consul-template.templates_rendered` | id=templateID, status=(rendered\|would\|quiescence) | A counter of templates rendered |
+| `consul-template.runner_actions` | action=(start\|stop\|run) | A count of runner actions |
+| `consul-template.commands_exec` | status=(success\|error) | The number of commands executed after rendering templates |
+
+#### Metrics yet to be implemented
+
+The current metrics were implemented by takin as reference the [previous metric-related PR](https://github.com/hashicorp/consul-template/pull/1378/files#diff-d980d9aed26114a3414812b58d45770a201c1f29b7f67ddc0ef0891a8f1b7736), but as the `armon/go-metrics` library doesn't implement all types of metrics yet, histogram metrics could not be implemented.
+
+Said metrics are described as below:
+
+| Metric Name | Labels | Description |
+|-|:-:|-|
+| `consul-template.dependencies` | type=(consul\|vault\|local) | The number of dependencies grouped by types |
+| `consul-template.templates` | | The number of templates configured |
+| `consul-template.commands_exec_time` | id=tmplDestination | The execution time (seconds) of a template command |
+
+
+### Metric Samples
+
+#### DogStatsD
+
+```
+2020-05-05 11:57:46.143979 consul-template.runner_actions:1|c|#action:start
+consul-template.runner_actions:2|c|#action:run
+consul-template.dependencies_received:1|c|#id:kv.block(hello),type:consul
+consul-template.templates_rendered:1|c|#id:aadcafd7f28f1d9fc5e76ab2e029f844,status:rendered
+consul-template.commands_exec:1|c|#status:success
+consul-template.commands_exec:0|c|#status:error
+```
+
+#### Prometheus
+
+```
+$ curl localhost:8888/metrics
+# HELP consul_template_commands_exec The number of commands executed with labels status=(success|error)
+# TYPE consul_template_commands_exec counter
+consul_template_commands_exec{status="error"} 0
+consul_template_commands_exec{status="success"} 1
+# HELP consul_template_dependencies_received A counter of dependencies received with labels type=(consul|vault|local) and id=dependencyString
+# TYPE consul_template_dependencies_received counter
+consul_template_dependencies_received{id="kv.block(hello)",type="consul"} 1
+# HELP consul_template_runner_actions A count of runner actions with labels action=(start|stop|run)
+# TYPE consul_template_runner_actions counter
+consul_template_runner_actions{action="run"} 2
+consul_template_runner_actions{action="start"} 1
+# HELP consul_template_templates_rendered A counter of templates rendered with labels id=templateID and status=(rendered|would|quiescence)
+# TYPE consul_template_templates_rendered counter
+consul_template_templates_rendered{id="aadcafd7f28f1d9fc5e76ab2e029f844",status="rendered"} 1
+```
+
 ## FAQ
 
 **Q: How is this different than confd?**<br>

cli.go

@@ -20,6 +20,7 @@ import (
 	"github.com/hashicorp/consul-template/manager"
 	"github.com/hashicorp/consul-template/service_os"
 	"github.com/hashicorp/consul-template/signals"
+	"github.com/hashicorp/consul-template/telemetry"
 	"github.com/hashicorp/consul-template/version"
 )
 
@@ -132,6 +133,13 @@ func (cli *CLI) Run(args []string) int {
 		}
 	}()
 
+	// 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

@@ -82,6 +82,9 @@ 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"`
 
@@ -174,6 +177,10 @@ 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()
 	}
@@ -265,6 +272,10 @@ 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)
 	}
@@ -336,6 +347,7 @@ func Parse(s string) (*Config, error) {
 		"nomad.transport",
 		"ssl",
 		"syslog",
+		"telemetry",
 		"vault",
 		"vault.retry",
 		"vault.ssl",
@@ -494,6 +506,7 @@ func (c *Config) GoString() string {
 		"ReloadSignal:%s, "+
 		"FileLog:%#v, "+
 		"Syslog:%#v, "+
+		"Telemetry:%#v, "+
 		"Templates:%#v, "+
 		"TemplateErrFatal:%#v"+
 		"Vault:%#v, "+
@@ -513,6 +526,7 @@ func (c *Config) GoString() string {
 		SignalGoString(c.ReloadSignal),
 		c.FileLog,
 		c.Syslog,
+		c.Telemetry.GoString(),
 		c.Templates,
 		c.TemplateErrFatal,
 		c.Vault,
@@ -561,6 +575,7 @@ func DefaultConfig() *Config {
 		FileLog:       DefaultLogFileConfig(),
 		Nomad:         DefaultNomadConfig(),
 		Syslog:        DefaultSyslogConfig(),
+		Telemetry:     DefaultTelemetryConfig(),
 		Templates:     DefaultTemplateConfigs(),
 		Vault:         DefaultVaultConfig(),
 		Wait:          DefaultWaitConfig(),
@@ -634,6 +649,11 @@ 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/syslog.go

@@ -99,7 +99,7 @@ func (c *SyslogConfig) GoString() string {
 
 	return fmt.Sprintf("&SyslogConfig{"+
 		"Enabled:%s, "+
-		"Facility:%s"+
+		"Facility:%s, "+
 		"Name:%s"+
 		"}",
 		BoolGoString(c.Enabled),