Add a common collector interface (#521)

This provides the groundwork to refactor the collectors into a more consistent interface. It borrows some influence from the node_exporter with the goal to easily filter in/out collector modules. The execute func also provides a context for potential cancellation.

Signed-off-by: Joe Adams <github@joeadams.io>

Author: sysadmind

collector/cluster_health.go

@@ -26,10 +26,6 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 )
 
-const (
-	namespace = "elasticsearch"
-)
-
 var (
 	colors                     = []string{"green", "yellow", "red"}
 	defaultClusterHealthLabels = []string{"cluster"}

collector/collector.go

@@ -0,0 +1,100 @@
+// Copyright 2022 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package collector includes all individual collectors to gather and export elasticsearch metrics.
+package collector
+
+import (
+	"context"
+	"net/http"
+	"net/url"
+	"sync"
+	"time"
+
+	"github.com/go-kit/log"
+	"github.com/go-kit/log/level"
+	"github.com/prometheus/client_golang/prometheus"
+)
+
+// Namespace defines the common namespace to be used by all metrics.
+const namespace = "elasticsearch"
+
+var (
+	scrapeDurationDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, "scrape", "duration_seconds"),
+		"elasticsearch_exporter: Duration of a collector scrape.",
+		[]string{"collector"},
+		nil,
+	)
+	scrapeSuccessDesc = prometheus.NewDesc(
+		prometheus.BuildFQName(namespace, "scrape", "success"),
+		"elasticsearch_exporter: Whether a collector succeeded.",
+		[]string{"collector"},
+		nil,
+	)
+)
+
+// Collector is the interface a collector has to implement.
+type Collector interface {
+	// Get new metrics and expose them via prometheus registry.
+	Update(context.Context, chan<- prometheus.Metric) error
+}
+
+type ElasticsearchCollector struct {
+	Collectors map[string]Collector
+	logger     log.Logger
+}
+
+// NewElasticsearchCollector creates a new ElasticsearchCollector
+func NewElasticsearchCollector(logger log.Logger, httpClient *http.Client, esURL *url.URL) (*ElasticsearchCollector, error) {
+	collectors := make(map[string]Collector)
+
+	return &ElasticsearchCollector{Collectors: collectors, logger: logger}, nil
+}
+
+// Describe implements the prometheus.Collector interface.
+func (e ElasticsearchCollector) Describe(ch chan<- *prometheus.Desc) {
+	ch <- scrapeDurationDesc
+	ch <- scrapeSuccessDesc
+}
+
+// Collect implements the prometheus.Collector interface.
+func (e ElasticsearchCollector) Collect(ch chan<- prometheus.Metric) {
+	wg := sync.WaitGroup{}
+	ctx := context.TODO()
+	wg.Add(len(e.Collectors))
+	for name, c := range e.Collectors {
+		go func(name string, c Collector) {
+			execute(ctx, name, c, ch, e.logger)
+			wg.Done()
+		}(name, c)
+	}
+	wg.Wait()
+}
+
+func execute(ctx context.Context, name string, c Collector, ch chan<- prometheus.Metric, logger log.Logger) {
+	begin := time.Now()
+	err := c.Update(ctx, ch)
+	duration := time.Since(begin)
+	var success float64
+
+	if err != nil {
+		_ = level.Error(logger).Log("msg", "collector failed", "name", name, "duration_seconds", duration.Seconds(), "err", err)
+		success = 0
+	} else {
+		_ = level.Debug(logger).Log("msg", "collector succeeded", "name", name, "duration_seconds", duration.Seconds())
+		success = 1
+	}
+	ch <- prometheus.MustNewConstMetric(scrapeDurationDesc, prometheus.GaugeValue, duration.Seconds(), name)
+	ch <- prometheus.MustNewConstMetric(scrapeSuccessDesc, prometheus.GaugeValue, success, name)
+}