Add NATS output plugin.

Added NATS server container needed for tests.

Added NATS output plug-in. Fixes #1487

NATS output plug-in use internal.GetTLSConfig to instrument TLS configuration.

Added NATS output plug-in to changelog.

closes #1487
closes #1697

plugins/outputs/nats/README.md

@@ -0,0 +1,37 @@
+# NATS Output Plugin
+
+This plugin writes to a (list of) specified NATS instance(s).
+ 
+```
+[[outputs.nats]]
+  ## URLs of NATS servers
+  servers = ["nats://localhost:4222"]
+  ## Optional credentials
+  # username = ""
+  # password = ""
+  ## NATS subject for producer messages
+  subject = "telegraf"
+  ## Optional TLS Config
+  ## CA certificate used to self-sign NATS server(s) TLS certificate(s)
+  # tls_ca = "/etc/telegraf/ca.pem"
+  ## Use TLS but skip chain & host verification
+  # insecure_skip_verify = false
+
+  ## Data format to output.
+  ## Each data format has it's own unique set of configuration options, read
+  ## more about them here:
+  ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_OUTPUT.md
+  data_format = "influx"
+```
+
+### Required parameters:
+
+* `servers`:  List of strings, this is for NATS clustering support. Each URL should start with `nats://`.
+* `subject`: The NATS subject to publish to.
+
+### Optional parameters:
+
+* `username`: Username for NATS
+* `password`: Password for NATS
+* `tls_ca`: TLS CA
+* `insecure_skip_verify`: Use SSL but skip chain & host verification (default: false)

plugins/outputs/nats/nats.go

@@ -0,0 +1,129 @@
+package nats
+
+import (
+	"fmt"
+
+	nats_client "github.com/nats-io/nats"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal"
+	"github.com/influxdata/telegraf/plugins/outputs"
+	"github.com/influxdata/telegraf/plugins/serializers"
+)
+
+type NATS struct {
+	// Servers is the NATS server pool to connect to
+	Servers []string
+	// Credentials
+	Username string
+	Password string
+	// NATS subject to publish metrics to
+	Subject string
+
+	// Path to CA file
+	CAFile string `toml:"tls_ca"`
+
+	// Skip SSL verification
+	InsecureSkipVerify bool
+
+	conn       *nats_client.Conn
+	serializer serializers.Serializer
+}
+
+var sampleConfig = `
+  ## URLs of NATS servers
+  servers = ["nats://localhost:4222"]
+  ## Optional credentials
+  # username = ""
+  # password = ""
+  ## NATS subject for producer messages
+  subject = "telegraf"
+  ## Optional TLS Config
+  ## CA certificate used to self-sign NATS server(s) TLS certificate(s)
+  # tls_ca = "/etc/telegraf/ca.pem"
+  ## Use TLS but skip chain & host verification
+  # insecure_skip_verify = false
+
+  ## Data format to output.
+  ## Each data format has it's own unique set of configuration options, read
+  ## more about them here:
+  ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_OUTPUT.md
+  data_format = "influx"
+`
+
+func (n *NATS) SetSerializer(serializer serializers.Serializer) {
+	n.serializer = serializer
+}
+
+func (n *NATS) Connect() error {
+	var err error
+	// set NATS connection options
+	opts := nats_client.DefaultOptions
+	opts.Servers = n.Servers
+	if n.Username != "" {
+		opts.User = n.Username
+		opts.Password = n.Password
+	}
+
+	// is TLS enabled?
+	tlsConfig, err := internal.GetTLSConfig(
+		"", "", n.CAFile, n.InsecureSkipVerify)
+	if err != nil {
+		return err
+	}
+	if tlsConfig != nil {
+		// set NATS connection TLS options
+		opts.Secure = true
+		opts.TLSConfig = tlsConfig
+	}
+
+	// try and connect
+	n.conn, err = opts.Connect()
+
+	return err
+}
+
+func (n *NATS) Close() error {
+	n.conn.Close()
+	return nil
+}
+
+func (n *NATS) SampleConfig() string {
+	return sampleConfig
+}
+
+func (n *NATS) Description() string {
+	return "Send telegraf measurements to NATS"
+}
+
+func (n *NATS) Write(metrics []telegraf.Metric) error {
+	if len(metrics) == 0 {
+		return nil
+	}
+
+	for _, metric := range metrics {
+		values, err := n.serializer.Serialize(metric)
+		if err != nil {
+			return err
+		}
+
+		var pubErr error
+		for _, value := range values {
+			err = n.conn.Publish(n.Subject, []byte(value))
+			if err != nil {
+				pubErr = err
+			}
+		}
+
+		if pubErr != nil {
+			return fmt.Errorf("FAILED to send NATS message: %s", err)
+		}
+	}
+	return nil
+}
+
+func init() {
+	outputs.Add("nats", func() telegraf.Output {
+		return &NATS{}
+	})
+}

plugins/outputs/nats/nats_test.go

@@ -0,0 +1,31 @@
+package nats
+
+import (
+	"testing"
+
+	"github.com/influxdata/telegraf/plugins/serializers"
+	"github.com/influxdata/telegraf/testutil"
+	"github.com/stretchr/testify/require"
+)
+
+func TestConnectAndWrite(t *testing.T) {
+	if testing.Short() {
+		t.Skip("Skipping integration test in short mode")
+	}
+
+	server := []string{"nats://" + testutil.GetLocalHost() + ":4222"}
+	s, _ := serializers.NewInfluxSerializer()
+	n := &NATS{
+		Servers:    server,
+		Subject:    "telegraf",
+		serializer: s,
+	}
+
+	// Verify that we can connect to the NATS daemon
+	err := n.Connect()
+	require.NoError(t, err)
+
+	// Verify that we can successfully write data to the NATS daemon
+	err = n.Write(testutil.MockMetrics())
+	require.NoError(t, err)
+}