feat: set a bind address and port with --listen-address

Allow providing a listening address to bind to as well as the port number with
a single new argument.

This is breaking the command line API if `--port` was used as this argument was
removed. For consistency with other exporters and general practices this approach
appeared more robust.

cmd/x509-certificate-exporter/main.go

@@ -16,7 +16,7 @@ import (
 func main() {
 	help := getopt.BoolLong("help", 'h', "show this help message and exit")
 	version := getopt.BoolLong("version", 'v', "show version info and exit")
-	port := getopt.IntLong("port", 'p', 9793, "prometheus exporter listening port")
+	listenAddress := getopt.StringLong("listen-address", 'b', ":9793", "address on which to bind and expose metrics")
 	debug := getopt.BoolLong("debug", 0, "enable debug mode")
 	trimPathComponents := getopt.IntLong("trim-path-components", 0, 0, "remove <n> leading component(s) from path(s) in label(s)")
 	exposeRelativeMetrics := getopt.BoolLong("expose-relative-metrics", 0, "expose additionnal metrics with relative durations instead of absolute timestamps")
@@ -69,7 +69,7 @@ func main() {
 	}
 
 	exporter := internal.Exporter{
-		Port:                  *port,
+		ListenAddress:         *listenAddress,
 		Files:                 files,
 		Directories:           directories,
 		YAMLs:                 yamls,

internal/exporter.go

@@ -18,7 +18,7 @@ import (
 
 // Exporter : Configuration (from command-line)
 type Exporter struct {
-	Port                  int
+	ListenAddress         string
 	Files                 []string
 	Directories           []string
 	YAMLs                 []string
@@ -65,10 +65,9 @@ func (exporter *Exporter) Listen() error {
 		}
 	}
 
-	listen := fmt.Sprintf(":%d", exporter.Port)
-	log.Infof("listening on %s", listen)
+	log.Infof("listening on %s", exporter.ListenAddress)
 
-	listener, err := net.Listen("tcp", listen)
+	listener, err := net.Listen("tcp", exporter.ListenAddress)
 	if err != nil {
 		return err
 	}

internal/exporter_test.go

@@ -28,14 +28,15 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+const listenAddress = "0.0.0.0:9793"
 const port = 9793
 
 func TestRegularStartup(t *testing.T) {
 	_, filename, _, _ := runtime.Caller(0)
 
 	e := &Exporter{
-		Port:  port,
-		Files: []string{path.Join(filepath.Dir(filename), "../test/basic.pem")},
+		ListenAddress: listenAddress,
+		Files:         []string{path.Join(filepath.Dir(filename), "../test/basic.pem")},
 	}
 
 	go e.ListenAndServe()
@@ -357,8 +358,8 @@ func TestErrorMetrics(t *testing.T) {
 }
 
 func TestBindAddrAlreadyInUse(t *testing.T) {
-	listener, _ := net.Listen("tcp", ":9793")
-	e := &Exporter{Port: 9793}
+	listener, _ := net.Listen("tcp", listenAddress)
+	e := &Exporter{ListenAddress: listenAddress}
 	err := e.ListenAndServe()
 	listener.Close()
 	assert.NotNil(t, err, "no error was returned for bind failure")
@@ -707,7 +708,7 @@ func checkLabels(t *testing.T, labels []*model.LabelPair, path string, isKube bo
 }
 
 func testRequest(t *testing.T, exporter *Exporter, cb func(metrics []model.MetricFamily)) {
-	exporter.Port = port
+	exporter.ListenAddress = listenAddress
 	if exporter.KubeSecretTypes == nil {
 		exporter.KubeSecretTypes = []string{"kubernetes.io/tls:tls.crt"}
 	}