Allow for TLS connections to ElasticSearch (#1398)

* Allow for TLS connections to ElasticSearch

Extremely similar implementation to the HTTP JSON module's
implementation of the same code.

* Changelog update

plugins/inputs/elasticsearch/README.md

@@ -11,6 +11,13 @@ and optionally [cluster](https://www.elastic.co/guide/en/elasticsearch/reference
   servers = ["http://localhost:9200"]
   local = true
   cluster_health = true
+
+  ## Optional SSL Config
+  # ssl_ca = "/etc/telegraf/ca.pem"
+  # ssl_cert = "/etc/telegraf/cert.pem"
+  # ssl_key = "/etc/telegraf/key.pem"
+  ## Use SSL but skip chain & host verification
+  # insecure_skip_verify = false
 ```
 
 ### Measurements & Fields:

plugins/inputs/elasticsearch/elasticsearch.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal"
 	"github.com/influxdata/telegraf/internal/errchan"
 	"github.com/influxdata/telegraf/plugins/inputs"
 	jsonparser "github.com/influxdata/telegraf/plugins/parsers/json"
@@ -67,25 +68,31 @@ const sampleConfig = `
 
   ## set cluster_health to true when you want to also obtain cluster level stats
   cluster_health = false
+
+  ## Optional SSL Config
+  # ssl_ca = "/etc/telegraf/ca.pem"
+  # ssl_cert = "/etc/telegraf/cert.pem"
+  # ssl_key = "/etc/telegraf/key.pem"
+  ## Use SSL but skip chain & host verification
+  # insecure_skip_verify = false
 `
 
 // Elasticsearch is a plugin to read stats from one or many Elasticsearch
 // servers.
 type Elasticsearch struct {
-	Local         bool
-	Servers       []string
-	ClusterHealth bool
-	client        *http.Client
+	Local              bool
+	Servers            []string
+	ClusterHealth      bool
+	SSLCA              string `toml:"ssl_ca"`   // Path to CA file
+	SSLCert            string `toml:"ssl_cert"` // Path to host cert file
+	SSLKey             string `toml:"ssl_key"`  // Path to cert key file
+	InsecureSkipVerify bool   // Use SSL but skip chain & host verification
+	client             *http.Client
 }
 
 // NewElasticsearch return a new instance of Elasticsearch
 func NewElasticsearch() *Elasticsearch {
-	tr := &http.Transport{ResponseHeaderTimeout: time.Duration(3 * time.Second)}
-	client := &http.Client{
-		Transport: tr,
-		Timeout:   time.Duration(4 * time.Second),
-	}
-	return &Elasticsearch{client: client}
+	return &Elasticsearch{}
 }
 
 // SampleConfig returns sample configuration for this plugin.
@@ -101,6 +108,15 @@ func (e *Elasticsearch) Description() string {
 // Gather reads the stats from Elasticsearch and writes it to the
 // Accumulator.
 func (e *Elasticsearch) Gather(acc telegraf.Accumulator) error {
+	if e.client == nil {
+		client, err := e.createHttpClient()
+
+		if err != nil {
+			return err
+		}
+		e.client = client
+	}
+
 	errChan := errchan.New(len(e.Servers))
 	var wg sync.WaitGroup
 	wg.Add(len(e.Servers))
@@ -128,6 +144,23 @@ func (e *Elasticsearch) Gather(acc telegraf.Accumulator) error {
 	return errChan.Error()
 }
 
+func (e *Elasticsearch) createHttpClient() (*http.Client, error) {
+	tlsCfg, err := internal.GetTLSConfig(e.SSLCert, e.SSLKey, e.SSLCA, e.InsecureSkipVerify)
+	if err != nil {
+		return nil, err
+	}
+	tr := &http.Transport{
+		ResponseHeaderTimeout: time.Duration(3 * time.Second),
+		TLSClientConfig:       tlsCfg,
+	}
+	client := &http.Client{
+		Transport: tr,
+		Timeout:   time.Duration(4 * time.Second),
+	}
+
+	return client, nil
+}
+
 func (e *Elasticsearch) gatherNodeStats(url string, acc telegraf.Accumulator) error {
 	nodeStats := &struct {
 		ClusterName string           `json:"cluster_name"`

plugins/inputs/elasticsearch/elasticsearch_test.go

@@ -38,7 +38,7 @@ func (t *transportMock) CancelRequest(_ *http.Request) {
 }
 
 func TestElasticsearch(t *testing.T) {
-	es := NewElasticsearch()
+	es := newElasticsearchWithClient()
 	es.Servers = []string{"http://example.com:9200"}
 	es.client.Transport = newTransportMock(http.StatusOK, statsResponse)
 
@@ -67,7 +67,7 @@ func TestElasticsearch(t *testing.T) {
 }
 
 func TestGatherClusterStats(t *testing.T) {
-	es := NewElasticsearch()
+	es := newElasticsearchWithClient()
 	es.Servers = []string{"http://example.com:9200"}
 	es.ClusterHealth = true
 	es.client.Transport = newTransportMock(http.StatusOK, clusterResponse)
@@ -87,3 +87,9 @@ func TestGatherClusterStats(t *testing.T) {
 		v2IndexExpected,
 		map[string]string{"index": "v2"})
 }
+
+func newElasticsearchWithClient() *Elasticsearch {
+	es := NewElasticsearch()
+	es.client = &http.Client{}
+	return es
+}