From d8a467128919cb86cf049bb996797cc55ea22f66 Mon Sep 17 00:00:00 2001
From: up2neck <163534172+up2neck@users.noreply.github.com>
Date: Tue, 3 Sep 2024 17:50:33 +0300
Subject: [PATCH] Fix agentcfg cache renewal scroll (#13958)

APM Agents configuration cache appears to be broken, resulting frequent invalid requests made by APM Server to Elasticsearch cluster. Fix ScrollID used for retrieval of APM Agents configuration.

(cherry picked from commit ecffa8e88d1d76831489e49e6bcd542749851eae)
---
 internal/agentcfg/elasticsearch.go | 46 ++++++++++++++----------------
 1 file changed, 22 insertions(+), 24 deletions(-)

diff --git a/internal/agentcfg/elasticsearch.go b/internal/agentcfg/elasticsearch.go
index b217882bfe7..066b9374817 100644
--- a/internal/agentcfg/elasticsearch.go
+++ b/internal/agentcfg/elasticsearch.go
@@ -251,40 +251,38 @@ func (f *ElasticsearchFetcher) refreshCache(ctx context.Context) (err error) {
 
 func (f *ElasticsearchFetcher) singlePageRefresh(ctx context.Context, scrollID string) (cacheResult, error) {
 	var result cacheResult
+	var err error
+	var resp *esapi.Response
 
-	if scrollID == "" {
-		resp, err := esapi.SearchRequest{
+	switch scrollID {
+	case "":
+		resp, err = esapi.SearchRequest{
 			Index:  []string{ElasticsearchIndexName},
 			Size:   &f.searchSize,
 			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.Debugf("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)
+	default:
+		resp, err = esapi.ScrollRequest{
+			ScrollID: scrollID,
+			Scroll:   f.cacheDuration,
+		}.Do(ctx, f.client)
 	}
-
-	resp, err := esapi.ScrollRequest{
-		ScrollID: result.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.Debugf("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)
 }