Add arbitrary labels on a per-database basis

README.md

@@ -721,6 +721,14 @@ databases:
     ## Oracle Database Connection pool minimum size
     # poolMinConnections: 15
 
+    ## Arbitrary labels to add to each metric scraped from this database
+    # labels:
+    #   - name: label_name
+    #     value: label_value
+    #   - name: label_name2
+    #     value: label_value2
+
+
 metrics:
   ## How often to scrape metrics. If not provided, metrics will be scraped on request.
   # scrapeInterval: 15s
@@ -791,6 +799,18 @@ databases:
     # poolMaxConnections: 15
     ## Oracle Database Connection pool minimum size
     # poolMinConnections: 15
+
+    ### Arbitrary labels to add to each metric scraped from this database
+    ## Any labels configured for one database will be added to metrics from
+    ## every database, because the same metric names must always have the same
+    ## full labelset. If the label isn't set for a particular database, then it
+    ## will just be set to an empty string.
+    # labels:
+    #   - name: label_name
+    #     value: label_value
+    #   - name: label_name2
+    #     value: label_value2
+
   db2:
     ## Database username
     username: ${DB2_USERNAME}
@@ -828,6 +848,17 @@ databases:
     ## Oracle Database Connection pool minimum size
     # poolMinConnections: 15
 
+    ### Arbitrary labels to add to each metric scraped from this database
+    ## Any labels configured for one database will be added to metrics from
+    ## every database, because the same metric names must always have the same
+    ## full labelset. If the label isn't set for a particular database, then it
+    ## will just be set to an empty string.
+    # labels:
+    #   - name: label_name
+    #     value: label_value
+    #   - name: label_name2
+    #     value: label_value2
+
 metrics:
   ## How often to scrape metrics. If not provided, metrics will be scraped on request.
   # scrapeInterval: 15s

collector/collector.go

@@ -14,6 +14,7 @@ import (
 	"io"
 	"log/slog"
 	"os"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -50,9 +51,23 @@ func maskDsn(dsn string) string {
 func NewExporter(logger *slog.Logger, m *MetricsConfiguration) *Exporter {
 	var databases []*Database
 	wg := &sync.WaitGroup{}
+
+	var allConstLabels []string
+	// All the metrics of the same name need to have the same labels
+	// If a label is set for a particular database, it must be included also
+	// in the same metrics collected from other databases. It will just be
+	// set to a blank value.
+	for _, dbconfig := range m.Databases {
+		for _, label := range dbconfig.Labels {
+			if (!slices.Contains(allConstLabels, label.Name)) {
+				allConstLabels = append(allConstLabels, label.Name)
+			}
+		}
+	}
+
 	for dbname, dbconfig := range m.Databases {
 		logger.Info("Initializing database", "database", dbname)
-		database := NewDatabase(logger, dbname, dbconfig)
+		database := NewDatabase(logger, dbname, dbconfig, allConstLabels)
 		databases = append(databases, database)
 		wg.Add(1)
 		go func() {
@@ -400,6 +415,7 @@ func (e *Exporter) scrapeGenericValues(d *Database, ch chan<- prometheus.Metric,
 	fieldToAppend string, ignoreZeroResult bool, request string, queryTimeout time.Duration) error {
 	metricsCount := 0
 	constLabels := d.constLabels()
+	e.logger.Debug("labels", constLabels)
 	genericParser := func(row map[string]string) error {
 		// Construct labels value
 		labelsValues := []string{}

collector/config.go

@@ -27,6 +27,7 @@ type DatabaseConfig struct {
 	URL           string `yaml:"url"`
 	ConnectConfig `yaml:",inline"`
 	Vault         *VaultConfig `yaml:"vault,omitempty"`
+	Labels        []DatabaseLabel `yaml:"labels,omitempty"`
 }
 
 type ConnectConfig struct {
@@ -72,6 +73,11 @@ type LoggingConfig struct {
 	LogDestination string         `yaml:"destination"`
 }
 
+type DatabaseLabel struct {
+	Name string `yaml:"name"`
+	Value string `yaml:"value"`
+}
+
 func (m *MetricsConfiguration) LogDestination() string {
 	return m.Logging.LogDestination
 }

collector/database.go

@@ -66,19 +66,33 @@ func (d *Database) ping(logger *slog.Logger) error {
 }
 
 func (d *Database) constLabels() map[string]string {
-	return map[string]string{
+	// database name always included in constLabels
+	labels := map[string]string{
 		"database": d.Name,
 	}
+	// All the metrics of the same name need to have the same labels
+	// If a label is set for a particular database, it must be included also
+	// in the same metrics collected from other databases. It will just be
+	// set to a blank value.
+	for _, label := range d.allConstLabels {
+		labels[label] = ""
+	}
+	// configured per-database labels added to constLabels
+	for _, label := range d.Config.Labels {
+		labels[label.Name] = label.Value
+	}
+	return labels
 }
 
-func NewDatabase(logger *slog.Logger, dbname string, dbconfig DatabaseConfig) *Database {
+func NewDatabase(logger *slog.Logger, dbname string, dbconfig DatabaseConfig, allConstLabels []string) *Database {
 	db, dbtype := connect(logger, dbname, dbconfig)
 	return &Database{
-		Name:    dbname,
-		Up:      0,
-		Session: db,
-		Type:    dbtype,
-		Config:  dbconfig,
+		Name:            dbname,
+		Up:              0,
+		Session:         db,
+		Type:            dbtype,
+		Config:          dbconfig,
+		allConstLabels:  allConstLabels,
 	}
 }
 

collector/types.go

@@ -27,11 +27,12 @@ type Exporter struct {
 }
 
 type Database struct {
-	Name    string
-	Up      float64
-	Session *sql.DB
-	Type    float64
-	Config  DatabaseConfig
+	Name            string
+	Up              float64
+	Session         *sql.DB
+	Type            float64
+	Config          DatabaseConfig
+	allConstLabels  []string
 }
 
 type Config struct {