Support InfluxDB clusters

Closes #143

outputs/influxdb/influxdb.go

@@ -1,8 +1,10 @@
 package influxdb
 
 import (
+	"errors"
 	"fmt"
 	"log"
+	"math/rand"
 	"net/url"
 	"strings"
 
@@ -12,19 +14,23 @@ import (
 )
 
 type InfluxDB struct {
+	// URL is only for backwards compatability
 	URL       string
+	URLs      []string `toml:"urls"`
 	Username  string
 	Password  string
 	Database  string
 	UserAgent string
 	Timeout   t.Duration
 
-	conn *client.Client
+	conns []*client.Client
 }
 
 var sampleConfig = `
 	# The full HTTP endpoint URL for your InfluxDB instance
-	url = "http://localhost:8086" # required.
+	# Multiple urls can be specified for InfluxDB cluster support. Server to
+	# write to will be randomly chosen each interval.
+	urls = ["http://localhost:8086"] # required.
 
 	# The target database for metrics. This database must already exist
 	database = "telegraf" # required.
@@ -42,33 +48,58 @@ var sampleConfig = `
 `
 
 func (i *InfluxDB) Connect() error {
-	u, err := url.Parse(i.URL)
-	if err != nil {
-		return err
+	var urls []*url.URL
+	for _, URL := range i.URLs {
+		u, err := url.Parse(URL)
+		if err != nil {
+			return err
+		}
+		urls = append(urls, u)
 	}
 
-	c, err := client.NewClient(client.Config{
-		URL:       *u,
-		Username:  i.Username,
-		Password:  i.Password,
-		UserAgent: i.UserAgent,
-		Timeout:   i.Timeout.Duration,
-	})
-
-	if err != nil {
-		return err
+	// Backward-compatability with single Influx URL config files
+	// This could eventually be removed in favor of specifying the urls as a list
+	if i.URL != "" {
+		u, err := url.Parse(i.URL)
+		if err != nil {
+			return err
+		}
+		urls = append(urls, u)
 	}
 
-	_, err = c.Query(client.Query{
-		Command: fmt.Sprintf("CREATE DATABASE %s", i.Database),
-	})
-
-	if err != nil && !strings.Contains(err.Error(), "database already exists") {
-		log.Fatal(err)
+	var conns []*client.Client
+	for _, parsed_url := range urls {
+		c, err := client.NewClient(client.Config{
+			URL:       *parsed_url,
+			Username:  i.Username,
+			Password:  i.Password,
+			UserAgent: i.UserAgent,
+			Timeout:   i.Timeout.Duration,
+		})
+		if err != nil {
+			return err
+		}
+		conns = append(conns, c)
 	}
 
-	i.conn = c
-	return nil
+	// This will get set to nil if a successful connection is made
+	err := errors.New("Could not create database on any server")
+
+	for _, conn := range conns {
+		_, e := conn.Query(client.Query{
+			Command: fmt.Sprintf("CREATE DATABASE %s", i.Database),
+		})
+
+		if e != nil && !strings.Contains(e.Error(), "database already exists") {
+			log.Println("ERROR: " + e.Error())
+		} else {
+			err = nil
+			break
+		}
+	}
+
+	i.conns = conns
+	return err
 }
 
 func (i *InfluxDB) Close() error {
@@ -84,12 +115,24 @@ func (i *InfluxDB) Description() string {
 	return "Configuration for influxdb server to send metrics to"
 }
 
+// Choose a random server in the cluster to write to until a successful write
+// occurs, logging each unsuccessful. If all servers fail, return error.
 func (i *InfluxDB) Write(bp client.BatchPoints) error {
 	bp.Database = i.Database
-	if _, err := i.conn.Write(bp); err != nil {
-		return err
+
+	// This will get set to nil if a successful write occurs
+	err := errors.New("Could not write to any InfluxDB server in cluster")
+
+	p := rand.Perm(len(i.conns))
+	for _, n := range p {
+		if _, e := i.conns[n].Write(bp); e != nil {
+			log.Println("ERROR: " + e.Error())
+		} else {
+			err = nil
+			break
+		}
 	}
-	return nil
+	return err
 }
 
 func init() {