feat(database_observability.postgres): Embed prometheus exporter within db-o11y component

internal/component/database_observability/postgres/component.go

@@ -5,13 +5,16 @@ import (
 	"crypto/sha256"
 	"database/sql"
 	"fmt"
+	"log/slog"
 	"net/http"
 	"path"
 	"strings"
 	"sync"
 	"time"
 
 	"github.com/lib/pq"
+	pg_collector "github.com/prometheus-community/postgres_exporter/collector"
+	pg_exporter "github.com/prometheus-community/postgres_exporter/exporter"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/prometheus/common/model"
@@ -23,7 +26,9 @@ import (
 	"github.com/grafana/alloy/internal/component/database_observability"
 	"github.com/grafana/alloy/internal/component/database_observability/postgres/collector"
 	"github.com/grafana/alloy/internal/component/discovery"
+	exporter_postgres "github.com/grafana/alloy/internal/component/prometheus/exporter/postgres"
 	"github.com/grafana/alloy/internal/featuregate"
+	"github.com/grafana/alloy/internal/runtime/logging"
 	"github.com/grafana/alloy/internal/runtime/logging/level"
 	http_service "github.com/grafana/alloy/internal/service/http"
 	"github.com/grafana/alloy/syntax"
@@ -68,12 +73,13 @@ type Arguments struct {
 	ExcludeDatabases  []string            `alloy:"exclude_databases,attr,optional"`
 	ExcludeUsers      []string            `alloy:"exclude_users,attr,optional"`
 
-	CloudProvider          *CloudProvider         `alloy:"cloud_provider,block,optional"`
-	QuerySampleArguments   QuerySampleArguments   `alloy:"query_samples,block,optional"`
-	QueryDetailsArguments  QueryDetailsArguments  `alloy:"query_details,block,optional"`
-	SchemaDetailsArguments SchemaDetailsArguments `alloy:"schema_details,block,optional"`
-	ExplainPlansArguments  ExplainPlansArguments  `alloy:"explain_plans,block,optional"`
-	HealthCheckArguments   HealthCheckArguments   `alloy:"health_check,block,optional"`
+	CloudProvider          *CloudProvider               `alloy:"cloud_provider,block,optional"`
+	QuerySampleArguments   QuerySampleArguments         `alloy:"query_samples,block,optional"`
+	QueryDetailsArguments  QueryDetailsArguments        `alloy:"query_details,block,optional"`
+	SchemaDetailsArguments SchemaDetailsArguments       `alloy:"schema_details,block,optional"`
+	ExplainPlansArguments  ExplainPlansArguments        `alloy:"explain_plans,block,optional"`
+	HealthCheckArguments   HealthCheckArguments         `alloy:"health_check,block,optional"`
+	PrometheusExporter     *PrometheusExporterArguments `alloy:"prometheus_exporter,block,optional"`
 }
 
 type CloudProvider struct {
@@ -145,6 +151,24 @@ type HealthCheckArguments struct {
 	CollectInterval time.Duration `alloy:"collect_interval,attr,optional"`
 }
 
+// PrometheusExporterArguments configures the embedded postgres_exporter scrapers.
+// When this block is present, postgres_exporter metrics are served alongside the
+// component's own metrics at the same /metrics endpoint.
+//
+// It is a distinct type (not an embedded struct) because the Alloy syntax
+// system does not support anonymous/embedded fields.
+// Note: data_source_names is ignored; the component's data_source_name is always used.
+type PrometheusExporterArguments exporter_postgres.Arguments
+
+func (a *PrometheusExporterArguments) SetToDefault() {
+	*a = PrometheusExporterArguments(exporter_postgres.DefaultArguments)
+}
+
+func (a *PrometheusExporterArguments) Validate() error {
+	args := exporter_postgres.Arguments(*a)
+	return args.Validate()
+}
+
 func (a *Arguments) SetToDefault() {
 	*a = DefaultArguments
 }
@@ -154,6 +178,9 @@ func (a *Arguments) Validate() error {
 	if err != nil {
 		return err
 	}
+	if a.PrometheusExporter != nil && len(a.Targets) > 0 {
+		return fmt.Errorf("prometheus_exporter and targets are mutually exclusive: use prometheus_exporter to embed the exporter, or targets to scrape an external one")
+	}
 	return nil
 }
 
@@ -176,19 +203,20 @@ type Collector interface {
 }
 
 type Component struct {
-	opts         component.Options
-	args         Arguments
-	handler      loki.LogsReceiver
-	fanout       *loki.Fanout
-	mut          sync.RWMutex
-	registry     *prometheus.Registry
-	baseTarget   discovery.Target
-	collectors   []Collector
-	instanceKey  string
-	dbConnection *sql.DB
-	healthErr    *atomic.String
-	openSQL      func(driverName, dataSourceName string) (*sql.DB, error)
-	logsReceiver loki.LogsReceiver
+	opts               component.Options
+	args               Arguments
+	handler            loki.LogsReceiver
+	fanout             *loki.Fanout
+	mut                sync.RWMutex
+	registry           *prometheus.Registry
+	baseTarget         discovery.Target
+	collectors         []Collector
+	instanceKey        string
+	dbConnection       *sql.DB
+	healthErr          *atomic.String
+	openSQL            func(driverName, dataSourceName string) (*sql.DB, error)
+	logsReceiver       loki.LogsReceiver
+	exporterCollectors []prometheus.Collector
 }
 
 func New(opts component.Options, args Arguments) (*Component, error) {
@@ -367,6 +395,59 @@ func (c *Component) connectAndStartCollectors(ctx context.Context) error {
 		cp = cloudProvider
 	}
 
+	for _, col := range c.exporterCollectors {
+		c.registry.Unregister(col)
+	}
+	c.exporterCollectors = nil
+
+	if c.args.PrometheusExporter != nil {
+		exporterArgs := exporter_postgres.Arguments(*c.args.PrometheusExporter)
+		slogLogger := slog.New(logging.NewSlogGoKitHandler(c.opts.Logger))
+		dsn := string(c.args.DataSourceName)
+
+		e := pg_exporter.NewExporter(
+			[]string{dsn},
+			slogLogger,
+			pg_exporter.DisableDefaultMetrics(exporterArgs.DisableDefaultMetrics),
+			pg_exporter.WithUserQueriesPath(exporterArgs.CustomQueriesConfigPath),
+			pg_exporter.DisableSettingsMetrics(exporterArgs.DisableSettingsMetrics),
+			pg_exporter.AutoDiscoverDatabases(true),
+			pg_exporter.ExcludeDatabases(c.args.ExcludeDatabases),
+			pg_exporter.WithMetricPrefix("pg"),
+		)
+		if err := c.registry.Register(e); err != nil {
+			return fmt.Errorf("failed to register prometheus_exporter: %w", err)
+		}
+		c.exporterCollectors = append(c.exporterCollectors, e)
+
+		if !exporterArgs.DisableDefaultMetrics {
+			collectorOpts := []pg_collector.Option{pg_collector.WithCollectionTimeout("10s")}
+			if exporterArgs.StatStatementFlags != nil {
+				collectorOpts = append(collectorOpts, pg_collector.WithStatStatementsConfig(pg_collector.StatStatementsConfig{
+					IncludeQuery:     exporterArgs.StatStatementFlags.IncludeQuery,
+					QueryLength:      exporterArgs.StatStatementFlags.QueryLength,
+					Limit:            exporterArgs.StatStatementFlags.Limit,
+					ExcludeDatabases: exporterArgs.StatStatementFlags.ExcludeDatabases,
+					ExcludeUsers:     exporterArgs.StatStatementFlags.ExcludeUsers,
+				}))
+			}
+			col, err := pg_collector.NewPostgresCollector(
+				slogLogger,
+				c.args.ExcludeDatabases,
+				dsn,
+				exporterArgs.EnabledCollectors,
+				collectorOpts...,
+			)
+			if err != nil {
+				return fmt.Errorf("failed to create postgres collector: %w", err)
+			}
+			if err := c.registry.Register(col); err != nil {
+				return fmt.Errorf("failed to register postgres collector: %w", err)
+			}
+			c.exporterCollectors = append(c.exporterCollectors, col)
+		}
+	}
+
 	allTargets := append([]discovery.Target{c.baseTarget}, c.args.Targets...)
 	targets := make([]discovery.Target, 0, len(allTargets))
 	for _, t := range allTargets {

internal/component/database_observability/postgres/component_test.go

@@ -19,6 +19,7 @@ import (
 	"github.com/grafana/alloy/internal/component/database_observability"
 	"github.com/grafana/alloy/internal/component/database_observability/postgres/collector"
 	"github.com/grafana/alloy/internal/component/discovery"
+	exporter_postgres "github.com/grafana/alloy/internal/component/prometheus/exporter/postgres"
 	http_service "github.com/grafana/alloy/internal/service/http"
 	"github.com/grafana/alloy/syntax"
 	"github.com/grafana/alloy/syntax/alloytypes"
@@ -734,3 +735,62 @@ func TestPostgres_Reconnection(t *testing.T) {
 		}
 	})
 }
+
+func Test_PrometheusExporterBlock(t *testing.T) {
+	t.Run("absent when not specified", func(t *testing.T) {
+		cfg := `
+			data_source_name = "postgresql://user:pass@localhost:5432/db"
+			forward_to = []
+			targets = []
+		`
+		var args Arguments
+		err := syntax.Unmarshal([]byte(cfg), &args)
+		require.NoError(t, err)
+		assert.Nil(t, args.PrometheusExporter)
+	})
+
+	t.Run("present with defaults when empty block", func(t *testing.T) {
+		cfg := `
+			data_source_name = "postgresql://user:pass@localhost:5432/db"
+			forward_to = []
+			targets = []
+			prometheus_exporter {}
+		`
+		var args Arguments
+		err := syntax.Unmarshal([]byte(cfg), &args)
+		require.NoError(t, err)
+		require.NotNil(t, args.PrometheusExporter)
+		exporterArgs := exporter_postgres.Arguments(*args.PrometheusExporter)
+		assert.False(t, exporterArgs.DisableDefaultMetrics)
+		assert.False(t, exporterArgs.DisableSettingsMetrics)
+	})
+
+	t.Run("present with explicit config", func(t *testing.T) {
+		cfg := `
+			data_source_name = "postgresql://user:pass@localhost:5432/db"
+			forward_to = []
+			targets = []
+			prometheus_exporter {
+				disable_settings_metrics = true
+			}
+		`
+		var args Arguments
+		err := syntax.Unmarshal([]byte(cfg), &args)
+		require.NoError(t, err)
+		require.NotNil(t, args.PrometheusExporter)
+		exporterArgs := exporter_postgres.Arguments(*args.PrometheusExporter)
+		assert.True(t, exporterArgs.DisableSettingsMetrics)
+	})
+
+	t.Run("error when both prometheus_exporter and targets are set", func(t *testing.T) {
+		cfg := `
+			data_source_name = "postgresql://user:pass@localhost:5432/db"
+			forward_to = []
+			targets = [{"__address__" = "localhost:9187"}]
+			prometheus_exporter {}
+		`
+		var args Arguments
+		err := syntax.Unmarshal([]byte(cfg), &args)
+		require.ErrorContains(t, err, "prometheus_exporter and targets are mutually exclusive")
+	})
+}