[receiver/prometheus] include scrape configs provided via `scrape_con…

…fig_files` (open-telemetry#34897)

**Description:** This PR fixes a bug in the prometheus receiver where
the scrape configs provided via `scrape_config_files` were not applied.
Using `scrape_config_files` instead of providing the scrape configs
directly does come with some limitations regarding the use of env vars,
as also mentioned in
open-telemetry#34786 (comment).

**Link to tracking Issue:** open-telemetry#34786

**Testing:** Added unit tests

---------

Signed-off-by: Florian Bacher <florian.bacher@dynatrace.com>
Co-authored-by: Antoine Toulme <antoine@toulme.name>
Co-authored-by: David Ashpole <dashpole@google.com>

.chloggen/prometheus-receiver-scrape-config.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: prometheusreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix the retrieval of scrape configurations by also considering scrape config files
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [34786]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

receiver/prometheusreceiver/config.go

@@ -40,12 +40,24 @@ type Config struct {
 
 // Validate checks the receiver configuration is valid.
 func (cfg *Config) Validate() error {
-	if (cfg.PrometheusConfig == nil || len(cfg.PrometheusConfig.ScrapeConfigs) == 0) && cfg.TargetAllocator == nil {
+	if !containsScrapeConfig(cfg) && cfg.TargetAllocator == nil {
 		return errors.New("no Prometheus scrape_configs or target_allocator set")
 	}
 	return nil
 }
 
+func containsScrapeConfig(cfg *Config) bool {
+	if cfg.PrometheusConfig == nil {
+		return false
+	}
+	scrapeConfigs, err := (*promconfig.Config)(cfg.PrometheusConfig).GetScrapeConfigs()
+	if err != nil {
+		return false
+	}
+
+	return len(scrapeConfigs) > 0
+}
+
 // PromConfig is a redeclaration of promconfig.Config because we need custom unmarshaling
 // as prometheus "config" uses `yaml` tags.
 type PromConfig promconfig.Config
@@ -87,7 +99,12 @@ func (cfg *PromConfig) Validate() error {
 		return fmt.Errorf("unsupported features:\n\t%s", strings.Join(unsupportedFeatures, "\n\t"))
 	}
 
-	for _, sc := range cfg.ScrapeConfigs {
+	scrapeConfigs, err := (*promconfig.Config)(cfg).GetScrapeConfigs()
+	if err != nil {
+		return err
+	}
+
+	for _, sc := range scrapeConfigs {
 		if err := validateHTTPClientConfig(&sc.HTTPClientConfig); err != nil {
 			return err
 		}

receiver/prometheusreceiver/config_test.go

@@ -106,6 +106,19 @@ func TestLoadTargetAllocatorConfig(t *testing.T) {
 	assert.Equal(t, promModel.Duration(5*time.Second), r2.PrometheusConfig.ScrapeConfigs[0].ScrapeInterval)
 }
 
+func TestValidateConfigWithScrapeConfigFiles(t *testing.T) {
+	cm, err := confmaptest.LoadConf(filepath.Join("testdata", "config_scrape_config_files.yaml"))
+	require.NoError(t, err)
+	factory := NewFactory()
+	cfg := factory.CreateDefaultConfig()
+
+	sub, err := cm.Sub(component.NewIDWithName(metadata.Type, "").String())
+	require.NoError(t, err)
+	require.NoError(t, sub.Unmarshal(cfg))
+
+	require.NoError(t, component.ValidateConfig(cfg))
+}
+
 func TestLoadConfigFailsOnUnknownSection(t *testing.T) {
 	cm, err := confmaptest.LoadConf(filepath.Join("testdata", "invalid-config-section.yaml"))
 	require.NoError(t, err)

receiver/prometheusreceiver/metrics_receiver_scrape_config_files_test.go

@@ -0,0 +1,69 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package prometheusreceiver
+
+import (
+	"fmt"
+	"os"
+	"testing"
+
+	"github.com/prometheus/prometheus/config"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/collector/pdata/pmetric"
+	semconv "go.opentelemetry.io/collector/semconv/v1.27.0"
+	"gopkg.in/yaml.v2"
+)
+
+var scrapeFileTargetPage = `
+# A simple counter
+# TYPE foo counter
+foo1 1
+`
+
+// TestScrapeConfigFiles validates that scrape configs provided via scrape_config_files are
+// also considered and added to the applied configuration
+
+func TestScrapeConfigFiles(t *testing.T) {
+	setMetricsTimestamp()
+	targets := []*testData{
+		{
+			name: "target1",
+			pages: []mockPrometheusResponse{
+				{code: 200, data: scrapeFileTargetPage},
+			},
+			validateFunc: verifyScrapeConfigFiles,
+		},
+	}
+
+	testComponent(t, targets, func(cfg *Config) {
+		// take the generated scrape config and move it into a file instead
+		marshalledScrapeConfigs, err := yaml.Marshal(cfg.PrometheusConfig.ScrapeConfigs)
+		require.NoError(t, err)
+		tmpDir := t.TempDir()
+		cfgFileName := fmt.Sprintf("%s/test-scrape-config.yaml", tmpDir)
+		scrapeConfigFileContent := fmt.Sprintf("scrape_configs:\n%s", string(marshalledScrapeConfigs))
+		err = os.WriteFile(cfgFileName, []byte(scrapeConfigFileContent), 0400)
+		require.NoError(t, err)
+		cfg.PrometheusConfig.ScrapeConfigs = []*config.ScrapeConfig{}
+		cfg.PrometheusConfig.ScrapeConfigFiles = []string{cfgFileName}
+	})
+}
+
+func verifyScrapeConfigFiles(t *testing.T, _ *testData, result []pmetric.ResourceMetrics) {
+	require.Len(t, result, 1)
+	serviceName, ok := result[0].Resource().Attributes().Get(semconv.AttributeServiceName)
+	assert.True(t, ok)
+	assert.Equal(t, "target1", serviceName.Str())
+	assert.Equal(t, 6, result[0].ScopeMetrics().At(0).Metrics().Len())
+	metricFound := false
+
+	for i := 0; i < result[0].ScopeMetrics().At(0).Metrics().Len(); i++ {
+		if result[0].ScopeMetrics().At(0).Metrics().At(i).Name() == "foo1" {
+			metricFound = true
+			break
+		}
+	}
+	assert.True(t, metricFound)
+}

receiver/prometheusreceiver/targetallocator/manager.go

@@ -158,6 +158,10 @@ func (m *Manager) sync(compareHash uint64, httpClient *http.Client) (uint64, err
 }
 
 func (m *Manager) applyCfg() error {
+	scrapeConfigs, err := m.promCfg.GetScrapeConfigs()
+	if err != nil {
+		return fmt.Errorf("could not get scrape configs: %w", err)
+	}
 	if !m.enableNativeHistograms {
 		// Enforce scraping classic histograms to avoid dropping them.
 		for _, scrapeConfig := range m.promCfg.ScrapeConfigs {
@@ -170,7 +174,7 @@ func (m *Manager) applyCfg() error {
 	}
 
 	discoveryCfg := make(map[string]discovery.Configs)
-	for _, scrapeConfig := range m.promCfg.ScrapeConfigs {
+	for _, scrapeConfig := range scrapeConfigs {
 		discoveryCfg[scrapeConfig.JobName] = scrapeConfig.ServiceDiscoveryConfigs
 		m.settings.Logger.Info("Scrape job added", zap.String("jobName", scrapeConfig.JobName))
 	}

receiver/prometheusreceiver/testdata/config_scrape_config_files.yaml

@@ -0,0 +1,8 @@
+prometheus:
+  trim_metric_suffixes: true
+  use_start_time_metric: true
+  start_time_metric_regex: '^(.+_)*process_start_time_seconds$'
+  report_extra_scrape_metrics: true
+  config:
+    scrape_config_files:
+      - ./testdata/scrape-config.yaml

receiver/prometheusreceiver/testdata/scrape-config.yaml

@@ -0,0 +1,3 @@
+scrape_configs:
+  - job_name: 'demo'
+    scrape_interval: 5s