refactor: 'instance' label replaced by 'target', is configurable

cmd/sql_exporter/main.go

@@ -39,6 +39,7 @@ var (
 
 func init() {
 	prometheus.MustRegister(version.NewCollector("sql_exporter"))
+	flag.StringVar(&cfg.TargetLabel, "config.target-label", "target", "Target label name")
 }
 
 func main() {

config/config.go

@@ -23,6 +23,8 @@ import (
 // and serves to help us avoid overflow/wraparound issues.
 const MaxInt32 int = 1<<31 - 1
 
+var TargetLabel string
+
 // Load attempts to parse the given config file and return a Config object.
 func Load(configFile string) (*Config, error) {
 	klog.Infof("Loading configuration from %s", configFile)
@@ -630,7 +632,7 @@ func checkLabel(label string, ctx ...string) error {
 	if label == "" {
 		return fmt.Errorf("empty label defined in %s", strings.Join(ctx, " "))
 	}
-	if label == "job" || label == "instance" {
+	if label == "job" || label == TargetLabel {
 		return fmt.Errorf("reserved label %q redefined in %s", label, strings.Join(ctx, " "))
 	}
 	return nil

job.go

@@ -31,8 +31,8 @@ func NewJob(jc *config.JobConfig, gc *config.GlobalConfig) (Job, errors.WithCont
 	for _, sc := range jc.StaticConfigs {
 		for tname, dsn := range sc.Targets {
 			constLabels := prometheus.Labels{
-				"job":      jc.Name,
-				"instance": tname,
+				"job":              jc.Name,
+				config.TargetLabel: tname,
 			}
 			for name, value := range sc.Labels {
 				// Shouldn't happen as there are sanity checks in config, but check nonetheless.

target.go

@@ -50,15 +50,15 @@ type target struct {
 	conn *sql.DB
 }
 
-// NewTarget returns a new Target with the given instance name, data source name, collectors and constant labels.
+// NewTarget returns a new Target with the given target name, data source name, collectors and constant labels.
 // An empty target name means the exporter is running in single target mode: no synthetic metrics will be exported.
 func NewTarget(
-	logContext, name, dsn string, ccs []*config.CollectorConfig, constLabels prometheus.Labels, gc *config.GlobalConfig) (
+	logContext, tname, dsn string, ccs []*config.CollectorConfig, constLabels prometheus.Labels, gc *config.GlobalConfig) (
 	Target, errors.WithContext,
 ) {
-	if name != "" {
-		logContext = fmt.Sprintf("%s, target=%q", logContext, name)
-		constLabels = prometheus.Labels{"instance": name}
+	if tname != "" {
+		logContext = fmt.Sprintf("%s, target=%q", logContext, tname)
+		constLabels = prometheus.Labels{config.TargetLabel: tname}
 	}
 
 	constLabelPairs := make([]*dto.LabelPair, 0, len(constLabels))
@@ -82,7 +82,7 @@ func NewTarget(
 	upDesc := NewAutomaticMetricDesc(logContext, upMetricName, upMetricHelp, prometheus.GaugeValue, constLabelPairs)
 	scrapeDurationDesc := NewAutomaticMetricDesc(logContext, scrapeDurationName, scrapeDurationHelp, prometheus.GaugeValue, constLabelPairs)
 	t := target{
-		name:               name,
+		name:               tname,
 		dsn:                dsn,
 		collectors:         collectors,
 		constLabels:        constLabels,