feat: add apm agent configuration package (#143)

* feat: add apm agent configuration package

* fix: improve fields alignment

Author: rogercoll

agentcfg/elasticsearch.go

@@ -0,0 +1,250 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you 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 agentcfg // import "github.com/elastic/opentelemetry-collector-components/internal/agentcfg"
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"go.uber.org/zap"
+
+	"github.com/elastic/go-elasticsearch/v8"
+	"github.com/elastic/go-elasticsearch/v8/esapi"
+)
+
+const ElasticsearchIndexName = ".apm-agent-configuration"
+
+const (
+	// ErrInfrastructureNotReady is returned when a fetch request comes in while
+	// the infrastructure is not ready to serve the request.
+	// This may happen when the local cache is not initialized and no fallback fetcher is configured.
+	ErrInfrastructureNotReady = "agentcfg infrastructure is not ready"
+
+	// ErrNoValidElasticsearchConfig is an error where the server is
+	// not properly configured to fetch agent configuration.
+	ErrNoValidElasticsearchConfig = "no valid elasticsearch config to fetch agent config"
+)
+
+const (
+	refreshCacheTimeout = 5 * time.Second
+	loggerRateLimit     = time.Minute
+)
+
+// TODO:
+// - Add Otel tracer
+// - Collection metrics
+type ElasticsearchFetcher struct {
+	last             time.Time
+	client           *elasticsearch.Client
+	logger           *zap.Logger
+	cache            []AgentConfig
+	cacheDuration    time.Duration
+	searchSize       int
+	mu               sync.RWMutex
+	invalidESCfg     atomic.Bool
+	cacheInitialized atomic.Bool
+}
+
+func NewElasticsearchFetcher(
+	client *elasticsearch.Client,
+	cacheDuration time.Duration,
+	logger *zap.Logger,
+) *ElasticsearchFetcher {
+	return &ElasticsearchFetcher{
+		client:        client,
+		cacheDuration: cacheDuration,
+		searchSize:    100,
+		logger:        logger,
+	}
+}
+
+// Fetch finds a matching agent config based on the received query.
+func (f *ElasticsearchFetcher) Fetch(ctx context.Context, query Query) (Result, error) {
+	if f.cacheInitialized.Load() {
+		// Happy path: serve fetch requests using an initialized cache.
+		f.mu.RLock()
+		defer f.mu.RUnlock()
+		return matchAgentConfig(query, f.cache), nil
+	}
+
+	if f.invalidESCfg.Load() {
+		return Result{}, errors.New(ErrNoValidElasticsearchConfig)
+	}
+
+	return Result{}, errors.New(ErrInfrastructureNotReady)
+}
+
+// Run refreshes the fetcher cache by querying Elasticsearch periodically.
+func (f *ElasticsearchFetcher) Run(ctx context.Context) error {
+	refresh := func() bool {
+		// refresh returns a bool that indicates whether Run should return
+		// immediately without error, e.g. due to invalid Elasticsearch config.
+		if err := f.refreshCache(ctx); err != nil {
+
+			f.logger.Error(fmt.Sprintf("refresh cache error: %s", err))
+			if f.invalidESCfg.Load() {
+				f.logger.Warn("stopping refresh cache background job: elasticsearch config is invalid")
+				return true
+			}
+		} else {
+			f.logger.Debug("refresh cache success")
+		}
+		return false
+	}
+
+	// Trigger initial run.
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	default:
+		if stop := refresh(); stop {
+			return nil
+		}
+	}
+
+	// Then schedule subsequent runs.
+	t := time.NewTicker(f.cacheDuration)
+	defer t.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+		case <-t.C:
+			if stop := refresh(); stop {
+				return nil
+			}
+		}
+	}
+}
+
+type cacheResult struct {
+	ScrollID string `json:"_scroll_id"`
+	Hits     struct {
+		Hits []struct {
+			Source struct {
+				Settings map[string]string `json:"settings"`
+				Service  struct {
+					Name        string `json:"name"`
+					Environment string `json:"environment"`
+				} `json:"service"`
+				AgentName string `json:"agent_name"`
+				ETag      string `json:"etag"`
+			} `json:"_source"`
+		} `json:"hits"`
+	} `json:"hits"`
+}
+
+func (f *ElasticsearchFetcher) refreshCache(ctx context.Context) (err error) {
+	scrollID := ""
+	buffer := make([]AgentConfig, 0, len(f.cache))
+
+	// The refresh cache operation should complete within refreshCacheTimeout.
+	ctx, cancel := context.WithTimeout(ctx, refreshCacheTimeout)
+	defer cancel()
+
+	for {
+		result, err := f.singlePageRefresh(ctx, scrollID)
+		if err != nil {
+			f.clearScroll(ctx, scrollID)
+			return err
+		}
+
+		for _, hit := range result.Hits.Hits {
+			buffer = append(buffer, AgentConfig{
+				ServiceName:        hit.Source.Service.Name,
+				ServiceEnvironment: hit.Source.Service.Environment,
+				AgentName:          hit.Source.AgentName,
+				Etag:               hit.Source.ETag,
+				Config:             hit.Source.Settings,
+			})
+		}
+		scrollID = result.ScrollID
+		if len(result.Hits.Hits) == 0 {
+			break
+		}
+	}
+
+	f.clearScroll(ctx, scrollID)
+
+	f.mu.Lock()
+	f.cache = buffer
+	f.mu.Unlock()
+	f.cacheInitialized.Store(true)
+	f.last = time.Now()
+	return nil
+}
+
+func (f *ElasticsearchFetcher) clearScroll(ctx context.Context, scrollID string) {
+	resp, err := esapi.ClearScrollRequest{
+		ScrollID: []string{scrollID},
+	}.Do(ctx, f.client)
+	if err != nil {
+		f.logger.Warn(fmt.Sprintf("failed to clear scroll: %v", err))
+		return
+	}
+
+	if resp.IsError() {
+		f.logger.Warn(fmt.Sprintf("clearscroll request returned error: %s", resp.Status()))
+	}
+
+	resp.Body.Close()
+}
+
+func (f *ElasticsearchFetcher) singlePageRefresh(ctx context.Context, scrollID string) (cacheResult, error) {
+	var result cacheResult
+	var err error
+	var resp *esapi.Response
+
+	switch scrollID {
+	case "":
+		resp, err = esapi.SearchRequest{
+			Index:  []string{ElasticsearchIndexName},
+			Size:   &f.searchSize,
+			Scroll: f.cacheDuration,
+		}.Do(ctx, f.client)
+	default:
+		resp, err = esapi.ScrollRequest{
+			ScrollID: scrollID,
+			Scroll:   f.cacheDuration,
+		}.Do(ctx, f.client)
+	}
+	if err != nil {
+		return result, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode >= http.StatusBadRequest {
+		// Elasticsearch returns 401 on unauthorized requests and 403 on insufficient permission
+		if resp.StatusCode == http.StatusUnauthorized || resp.StatusCode == http.StatusForbidden {
+			f.invalidESCfg.Store(true)
+		}
+		bodyBytes, err := io.ReadAll(resp.Body)
+		if err == nil {
+			f.logger.Debug(fmt.Sprintf("refresh cache elasticsearch returned status %d: %s", resp.StatusCode, string(bodyBytes)))
+		}
+		return result, fmt.Errorf("refresh cache elasticsearch returned status %d", resp.StatusCode)
+	}
+	return result, json.NewDecoder(resp.Body).Decode(&result)
+}