Create a new cluster info retriever

This is an alternative implementation of the previous retriever in pkg/clusterinfo. The previous implementation required registering collectors and receiving updates over a channel. This InfoProvider instead provides a public method to get the cluster info with a cache to reduce network calls. The Collector.Update signature was also updated to take an UpdateContext. This UpdateContext can provide with an easy way to extend the context available during the Update calls on Collectors.

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

Author: sysadmind

cluster/provider.go

@@ -0,0 +1,117 @@
+// Copyright 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 cluster
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/url"
+	"path"
+	"sync"
+	"time"
+)
+
+type Info struct {
+	ClusterName string `json:"cluster_name"`
+}
+
+type InfoProvider struct {
+	logger          *slog.Logger
+	client          *http.Client
+	url             *url.URL
+	interval        time.Duration
+	lastClusterInfo Info
+	lastError       error
+	cachedAt        time.Time    // Time when the last cluster info was fetched
+	mu              sync.RWMutex // Protects lastClusterInfo, lastError, and cachedAt
+}
+
+// New creates a new Retriever.
+func NewInfoProvider(logger *slog.Logger, client *http.Client, u *url.URL, interval time.Duration) *InfoProvider {
+	return &InfoProvider{
+		logger:   logger,
+		client:   client,
+		url:      u,
+		interval: interval,
+	}
+}
+
+func (i *InfoProvider) GetInfo(ctx context.Context) (Info, error) {
+	i.mu.RLock()
+	info := i.lastClusterInfo
+	err := i.lastError
+	cachedAt := i.cachedAt
+
+	i.mu.RUnlock()
+
+	// If the cached info is recent enough, return it.
+	if !cachedAt.IsZero() && time.Since(cachedAt) < i.interval {
+
+		if err != nil {
+			return Info{}, err
+		}
+
+		if info.ClusterName != "" {
+			return info, nil
+		}
+	}
+
+	i.mu.Lock()
+	defer i.mu.Unlock()
+
+	// If we reach here, we need to fetch the cluster info. The cache is either empty or stale.
+	u := *i.url
+	u.Path = path.Join(u.Path, "/")
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
+	if err != nil {
+		return Info{}, err
+	}
+
+	resp, err := i.client.Do(req)
+	if err != nil {
+		i.logger.Error("failed to fetch cluster info", "err", err)
+		return Info{}, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		err = fmt.Errorf("unexpected status code: %d", resp.StatusCode)
+		i.lastError = err
+		return Info{}, err
+	}
+
+	var infoResponse Info
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		i.lastError = err
+		return Info{}, err
+	}
+
+	if err := json.Unmarshal(body, &infoResponse); err != nil {
+		i.lastError = err
+		return Info{}, fmt.Errorf("failed to unmarshal cluster info: %w", err)
+	}
+
+	info = Info{ClusterName: infoResponse.ClusterName}
+	i.lastClusterInfo = info
+	i.lastError = nil
+	i.cachedAt = time.Now()
+
+	return info, nil
+}

cluster/provider_test.go

@@ -0,0 +1,107 @@
+// Copyright 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 cluster
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"os"
+	"reflect"
+	"testing"
+	"time"
+
+	"github.com/prometheus/common/promslog"
+)
+
+func TestInfoProvider_GetInfo(t *testing.T) {
+	timesURLCalled := 0
+	expectedInfo := Info{
+		ClusterName: "test-cluster-1",
+	}
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/" {
+			http.NotFound(w, r)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		timesURLCalled++
+		_, _ = w.Write([]byte(`{
+			"name": "test-node-abcd",
+			"cluster_name": "test-cluster-1",
+			"cluster_uuid": "r1bT9sBrR7S9-CamE41Qqg",
+			"version": {
+				"number": "5.6.9",
+				"build_hash": "877a590",
+				"build_date": "2018-04-12T16:25:14.838Z",
+				"build_snapshot": false,
+				"lucene_version": "6.6.1"
+			}
+		}`))
+	}))
+	tsURL, err := url.Parse(ts.URL)
+	if err != nil {
+		t.Fatalf("failed to parse test server URL: %v", err)
+	}
+	defer ts.Close()
+
+	i := NewInfoProvider(promslog.New(&promslog.Config{Writer: os.Stdout}), http.DefaultClient, tsURL, time.Second)
+
+	if timesURLCalled != 0 {
+		t.Errorf("expected no initial URL calls, got %d", timesURLCalled)
+	}
+
+	got, err := i.GetInfo(context.Background())
+	if err != nil {
+		t.Errorf("InfoProvider.GetInfo() error = %v, wantErr %v", err, false)
+		return
+	}
+
+	if !reflect.DeepEqual(got, expectedInfo) {
+		t.Errorf("InfoProvider.GetInfo() = %v, want %v", got, expectedInfo)
+	}
+
+	if timesURLCalled != 1 {
+		t.Errorf("expected URL to be called once, got %d", timesURLCalled)
+	}
+
+	// Call again to ensure cached value is returned
+	got, err = i.GetInfo(context.Background())
+	if err != nil {
+		t.Errorf("InfoProvider.GetInfo() error on second call = %v, wantErr %v", err, false)
+		return
+	}
+	if !reflect.DeepEqual(got, expectedInfo) {
+		t.Errorf("InfoProvider.GetInfo() on second call = %v, want %v", got, expectedInfo)
+	}
+	if timesURLCalled != 1 {
+		t.Errorf("expected URL to be called only once, got %d", timesURLCalled)
+	}
+
+	// Call again after delay to ensure we refresh the cache
+	time.Sleep(2 * time.Second)
+	got, err = i.GetInfo(context.Background())
+	if err != nil {
+		t.Errorf("InfoProvider.GetInfo() error on second call = %v, wantErr %v", err, false)
+		return
+	}
+	if !reflect.DeepEqual(got, expectedInfo) {
+		t.Errorf("InfoProvider.GetInfo() on second call = %v, want %v", got, expectedInfo)
+	}
+	if timesURLCalled != 2 {
+		t.Errorf("expected URL to be called only once, got %d", timesURLCalled)
+	}
+
+}

collector/cluster_info.go

@@ -77,7 +77,7 @@ type VersionInfo struct {
 	LuceneVersion semver.Version `json:"lucene_version"`
 }
 
-func (c *ClusterInfoCollector) Update(_ context.Context, ch chan<- prometheus.Metric) error {
+func (c *ClusterInfoCollector) Update(_ context.Context, uc UpdateContext, ch chan<- prometheus.Metric) error {
 	resp, err := c.hc.Get(c.u.String())
 	if err != nil {
 		return err

collector/cluster_settings.go

@@ -145,7 +145,7 @@ type clusterSettingsWatermark struct {
 	Low        string `json:"low"`
 }
 
-func (c *ClusterSettingsCollector) Update(ctx context.Context, ch chan<- prometheus.Metric) error {
+func (c *ClusterSettingsCollector) Update(ctx context.Context, uc UpdateContext, ch chan<- prometheus.Metric) error {
 	u := c.u.ResolveReference(&url.URL{Path: "_cluster/settings"})
 	q := u.Query()
 	q.Set("include_defaults", "true")

collector/collector.go

@@ -25,6 +25,7 @@ import (
 	"time"
 
 	"github.com/alecthomas/kingpin/v2"
+	"github.com/prometheus-community/elasticsearch_exporter/cluster"
 	"github.com/prometheus/client_golang/prometheus"
 )
 
@@ -64,7 +65,7 @@ var (
 // 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
+	Update(context.Context, UpdateContext, chan<- prometheus.Metric) error
 }
 
 func registerCollector(name string, isDefaultEnabled bool, createFunc factoryFunc) {
@@ -92,6 +93,7 @@ type ElasticsearchCollector struct {
 	logger     *slog.Logger
 	esURL      *url.URL
 	httpClient *http.Client
+	cluserInfo *cluster.InfoProvider
 }
 
 type Option func(*ElasticsearchCollector) error
@@ -106,6 +108,10 @@ func NewElasticsearchCollector(logger *slog.Logger, filters []string, options ..
 		}
 	}
 
+	if e.cluserInfo == nil {
+		return nil, fmt.Errorf("cluster info provider is not set")
+	}
+
 	f := make(map[string]bool)
 	for _, filter := range filters {
 		enabled, exist := collectorState[filter]
@@ -155,6 +161,13 @@ func WithHTTPClient(hc *http.Client) Option {
 	}
 }
 
+func WithClusterInfoProvider(cl *cluster.InfoProvider) Option {
+	return func(e *ElasticsearchCollector) error {
+		e.cluserInfo = cl
+		return nil
+	}
+}
+
 // Describe implements the prometheus.Collector interface.
 func (e ElasticsearchCollector) Describe(ch chan<- *prometheus.Desc) {
 	ch <- scrapeDurationDesc
@@ -163,21 +176,22 @@ func (e ElasticsearchCollector) Describe(ch chan<- *prometheus.Desc) {
 
 // Collect implements the prometheus.Collector interface.
 func (e ElasticsearchCollector) Collect(ch chan<- prometheus.Metric) {
+	uc := NewDefaultUpdateContext(e.cluserInfo)
 	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)
+			execute(ctx, name, c, ch, e.logger, uc)
 			wg.Done()
 		}(name, c)
 	}
 	wg.Wait()
 }
 
-func execute(ctx context.Context, name string, c Collector, ch chan<- prometheus.Metric, logger *slog.Logger) {
+func execute(ctx context.Context, name string, c Collector, ch chan<- prometheus.Metric, logger *slog.Logger, uc UpdateContext) {
 	begin := time.Now()
-	err := c.Update(ctx, ch)
+	err := c.Update(ctx, uc, ch)
 	duration := time.Since(begin)
 	var success float64
 

collector/collector_test.go

@@ -16,6 +16,7 @@ package collector
 import (
 	"context"
 
+	"github.com/prometheus-community/elasticsearch_exporter/cluster"
 	"github.com/prometheus/client_golang/prometheus"
 )
 
@@ -32,5 +33,11 @@ func (w wrapCollector) Describe(_ chan<- *prometheus.Desc) {
 }
 
 func (w wrapCollector) Collect(ch chan<- prometheus.Metric) {
-	w.c.Update(context.Background(), ch)
+	w.c.Update(context.Background(), &mockUpdateContext{}, ch)
+}
+
+type mockUpdateContext struct{}
+
+func (m *mockUpdateContext) GetClusterInfo(_ context.Context) (cluster.Info, error) {
+	return cluster.Info{}, nil
 }

collector/data_stream.go

@@ -83,7 +83,7 @@ type DataStreamStatsDataStream struct {
 	MaximumTimestamp int64  `json:"maximum_timestamp"`
 }
 
-func (ds *DataStream) Update(ctx context.Context, ch chan<- prometheus.Metric) error {
+func (ds *DataStream) Update(ctx context.Context, uc UpdateContext, ch chan<- prometheus.Metric) error {
 	var dsr DataStreamStatsResponse
 
 	u := ds.u.ResolveReference(&url.URL{Path: "/_data_stream/*/_stats"})

collector/health_report.go

@@ -300,7 +300,7 @@ func statusValue(value string, color string) float64 {
 	return 0
 }
 
-func (c *HealthReport) Update(ctx context.Context, ch chan<- prometheus.Metric) error {
+func (c *HealthReport) Update(ctx context.Context, uc UpdateContext, ch chan<- prometheus.Metric) error {
 	u := c.url.ResolveReference(&url.URL{Path: "/_health_report"})
 	var healthReportResponse HealthReportResponse
 

collector/ilm.go

@@ -74,7 +74,7 @@ type IlmStatusResponse struct {
 	OperationMode string `json:"operation_mode"`
 }
 
-func (i *ILM) Update(ctx context.Context, ch chan<- prometheus.Metric) error {
+func (i *ILM) Update(ctx context.Context, uc UpdateContext, ch chan<- prometheus.Metric) error {
 	var ir IlmResponse
 
 	indexURL := i.u.ResolveReference(&url.URL{Path: "/_all/_ilm/explain"})

collector/slm.go

@@ -143,7 +143,7 @@ type SLMStatusResponse struct {
 	OperationMode string `json:"operation_mode"`
 }
 
-func (s *SLM) Update(ctx context.Context, ch chan<- prometheus.Metric) error {
+func (s *SLM) Update(ctx context.Context, uc UpdateContext, ch chan<- prometheus.Metric) error {
 	u := s.u.ResolveReference(&url.URL{Path: "/_slm/status"})
 	var slmStatusResp SLMStatusResponse