Add a config.data-source-name flag, to optionally override the config…

… file value, as requested in issue #7.

cmd/sql_exporter/main.go

@@ -15,6 +15,13 @@ import (
 	_ "net/http/pprof"
 )
 
+var (
+	showVersion   = flag.Bool("version", false, "Print version information.")
+	listenAddress = flag.String("web.listen-address", ":9399", "Address to listen on for web interface and telemetry.")
+	metricsPath   = flag.String("web.metrics-path", "/metrics", "Path under which to expose metrics.")
+	configFile    = flag.String("config.file", "sql_exporter.yml", "SQL Exporter configuration file name.")
+)
+
 func init() {
 	prometheus.MustRegister(version.NewCollector("sql_exporter"))
 }
@@ -25,13 +32,6 @@ func main() {
 		runtime.SetMutexProfileFraction(1)
 	}
 
-	var (
-		showVersion   = flag.Bool("version", false, "Print version information.")
-		listenAddress = flag.String("web.listen-address", ":9399", "Address to listen on for web interface and telemetry.")
-		metricsPath   = flag.String("web.metrics-path", "/metrics", "Path under which to expose metrics.")
-		configFile    = flag.String("config.file", "sql_exporter.yml", "SQL Exporter configuration file name.")
-	)
-
 	// Override --alsologtostderr default value.
 	if alsoLogToStderr := flag.Lookup("alsologtostderr"); alsoLogToStderr != nil {
 		alsoLogToStderr.DefValue = "true"

exporter.go

@@ -2,6 +2,7 @@ package sql_exporter
 
 import (
 	"context"
+	"flag"
 	"fmt"
 	"sync"
 
@@ -11,6 +12,8 @@ import (
 	dto "github.com/prometheus/client_model/go"
 )
 
+var dsnOverride = flag.String("config.data-source-name", "", "Data source name to override the value in the configuration file with.")
+
 // Exporter is a prometheus.Gatherer that gathers SQL metrics from targets and merges them with the default registry.
 type Exporter interface {
 	prometheus.Gatherer
@@ -35,6 +38,15 @@ func NewExporter(configFile string) (Exporter, error) {
 		return nil, err
 	}
 
+	// Override the DSN if requested (and in single target mode).
+	if *dsnOverride != "" {
+		if len(c.Jobs) > 0 {
+			return nil, fmt.Errorf("The config.data-source-name flag (value %q) only applies in single target mode", *dsnOverride)
+		} else {
+			c.Target.DSN = config.Secret(*dsnOverride)
+		}
+	}
+
 	var targets []Target
 	if c.Target != nil {
 		target, err := NewTarget("", "", string(c.Target.DSN), c.Target.Collectors(), nil, c.Globals)