Adding x-pack code for elasticsearch/index metricset (#8260)

* Updating test fixture

* Extract indicesStruct for reuse within package

* Only request specific stats

* Add X-Pack switch

* Adding explanatory comment

* Fleshing it out some more

* Remove empty TODO

* Adding reference comment for fields + refactoring into helper funcs

* Re-formatting

* Extract stats API metrics into own const

* Using errors.Wrap

* Adding logger to elasticsearch metricset

* Log errors

* Sharing the type not the variable 🤦

metricbeat/module/elasticsearch/cluster_stats/cluster_stats.go

@@ -27,7 +27,7 @@ import (
 )
 
 func init() {
-	mb.Registry.MustAddMetricSet("elasticsearch", "cluster_stats", New,
+	mb.Registry.MustAddMetricSet(elasticsearch.ModuleName, "cluster_stats", New,
 		mb.WithHostParser(elasticsearch.HostParser),
 		mb.WithNamespace("elasticsearch.cluster.stats"),
 	)

metricbeat/module/elasticsearch/cluster_stats/data_xpack.go

@@ -169,7 +169,8 @@ func eventMappingXPack(r mb.ReporterV2, m *MetricSet, content []byte) error {
 		return err
 	}
 
-	clusterState, err := elasticsearch.GetClusterState(m.HTTP, m.HTTP.GetURI())
+	clusterStateMetrics := []string{"version", "master_node", "nodes", "routing_table"}
+	clusterState, err := elasticsearch.GetClusterState(m.HTTP, m.HTTP.GetURI(), clusterStateMetrics)
 	if err != nil {
 		return err
 	}

metricbeat/module/elasticsearch/elasticsearch.go

@@ -21,6 +21,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/url"
+	"strings"
 	"sync"
 	"time"
 
@@ -32,6 +33,9 @@ import (
 // Global clusterIdCache. Assumption is that the same node id never can belong to a different cluster id
 var clusterIDCache = map[string]string{}
 
+// ModuleName is the ame of this module
+const ModuleName = "elasticsearch"
+
 // Info construct contains the data from the Elasticsearch / endpoint
 type Info struct {
 	ClusterName string `json:"cluster_name"`
@@ -202,8 +206,13 @@ func GetLicense(http *helper.HTTP, resetURI string) (common.MapStr, error) {
 }
 
 // GetClusterState returns cluster state information
-func GetClusterState(http *helper.HTTP, resetURI string) (common.MapStr, error) {
-	content, err := fetchPath(http, resetURI, "_cluster/state/version,master_node,nodes,routing_table")
+func GetClusterState(http *helper.HTTP, resetURI string, metrics []string) (common.MapStr, error) {
+	clusterStateURI := "_cluster/state"
+	if metrics != nil && len(metrics) > 0 {
+		clusterStateURI += "/" + strings.Join(metrics, ",")
+	}
+
+	content, err := fetchPath(http, resetURI, clusterStateURI)
 	if err != nil {
 		return nil, err
 	}