Add systemd socket listener activation (#95)

* add systemd socket listener activation

Signed-off-by: Perry Naseck <git@perrynaseck.com>

go.mod

@@ -3,9 +3,11 @@ module github.com/prometheus/exporter-toolkit
 go 1.17
 
 require (
+	github.com/coreos/go-systemd/v22 v22.3.2
 	github.com/go-kit/log v0.2.1
 	github.com/prometheus/common v0.37.0
 	golang.org/x/crypto v0.0.0-20220829220503-c86fa9a7ed90
+	golang.org/x/sync v0.0.0-20220601150217-0de741cfad7f
 	gopkg.in/alecthomas/kingpin.v2 v2.2.6
 	gopkg.in/yaml.v2 v2.4.0
 )

go.sum

@@ -89,6 +89,8 @@ github.com/cncf/xds/go v0.0.0-20210805033703-aa0b78936158/go.mod h1:eXthEFrGJvWH
 github.com/cncf/xds/go v0.0.0-20210922020428-25de7278fc84/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
 github.com/cncf/xds/go v0.0.0-20211001041855-01bcc9b48dfe/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
 github.com/cncf/xds/go v0.0.0-20211011173535-cb28da3451f1/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
+github.com/coreos/go-systemd/v22 v22.3.2 h1:D9/bQk5vlXQFZ6Kwuu6zaiXJ9oTPe68++AzAJc1DzSI=
+github.com/coreos/go-systemd/v22 v22.3.2/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -118,6 +120,7 @@ github.com/go-logfmt/logfmt v0.5.0/go.mod h1:wCYkCAKZfumFQihp8CzCvQ3paCTfi41vtzG
 github.com/go-logfmt/logfmt v0.5.1 h1:otpy5pqBCBZ1ng9RQ0dPu4PN7ba75Y/aA+UpowDyNVA=
 github.com/go-logfmt/logfmt v0.5.1/go.mod h1:WYhtIu8zTZfxdn5+rREduYbwxfcBr/Vr6KEVveWlfTs=
 github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
+github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
 github.com/gogo/protobuf v1.1.1/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7atdtwQ=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
 github.com/golang/groupcache v0.0.0-20190702054246-869f871628b6/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
@@ -417,6 +420,7 @@ golang.org/x/sync v0.0.0-20200625203802-6e8e738ad208/go.mod h1:RxMgew5VJxzue5/jJ
 golang.org/x/sync v0.0.0-20201020160332-67f06af15bc9/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20201207232520-09787c993a3a/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20220601150217-0de741cfad7f h1:Ax0t5p6N38Ga0dThY21weqDEyz2oklo4IvDkpigvkD8=
 golang.org/x/sync v0.0.0-20220601150217-0de741cfad7f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=

web/handler_test.go

@@ -24,7 +24,6 @@ import (
 // protected endpoint multiple times.
 func TestBasicAuthCache(t *testing.T) {
 	server := &http.Server{
-		Addr: port,
 		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			w.Write([]byte("Hello World!"))
 		}),
@@ -39,7 +38,12 @@ func TestBasicAuthCache(t *testing.T) {
 	})
 
 	go func() {
-		ListenAndServe(server, "testdata/web_config_users_noTLS.good.yml", testlogger)
+		flags := FlagConfig{
+			WebListenAddresses: &([]string{port}),
+			WebSystemdSocket:   OfBool(false),
+			WebConfigFile:      OfString("testdata/web_config_users_noTLS.good.yml"),
+		}
+		ListenAndServe(server, &flags, testlogger)
 		close(done)
 	}()
 
@@ -88,7 +92,6 @@ func TestBasicAuthCache(t *testing.T) {
 // to prevent user enumeration.
 func TestBasicAuthWithFakepassword(t *testing.T) {
 	server := &http.Server{
-		Addr: port,
 		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			w.Write([]byte("Hello World!"))
 		}),
@@ -103,7 +106,12 @@ func TestBasicAuthWithFakepassword(t *testing.T) {
 	})
 
 	go func() {
-		ListenAndServe(server, "testdata/web_config_users_noTLS.good.yml", testlogger)
+		flags := FlagConfig{
+			WebListenAddresses: &([]string{port}),
+			WebSystemdSocket:   OfBool(false),
+			WebConfigFile:      OfString("testdata/web_config_users_noTLS.good.yml"),
+		}
+		ListenAndServe(server, &flags, testlogger)
 		close(done)
 	}()
 
@@ -132,7 +140,6 @@ func TestBasicAuthWithFakepassword(t *testing.T) {
 // TestHTTPHeaders validates that HTTP headers are added correctly.
 func TestHTTPHeaders(t *testing.T) {
 	server := &http.Server{
-		Addr: port,
 		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			w.Write([]byte("Hello World!"))
 		}),
@@ -147,7 +154,12 @@ func TestHTTPHeaders(t *testing.T) {
 	})
 
 	go func() {
-		ListenAndServe(server, "testdata/web_config_headers.good.yml", testlogger)
+		flags := FlagConfig{
+			WebListenAddresses: &([]string{port}),
+			WebSystemdSocket:   OfBool(false),
+			WebConfigFile:      OfString("testdata/web_config_headers.good.yml"),
+		}
+		ListenAndServe(server, &flags, testlogger)
 		close(done)
 	}()
 

web/kingpinflag/flag.go

@@ -13,14 +13,34 @@
 package kingpinflag
 
 import (
+	"runtime"
+
 	"gopkg.in/alecthomas/kingpin.v2"
+
+	"github.com/prometheus/exporter-toolkit/web"
 )
 
 // AddFlags adds the flags used by this package to the Kingpin application.
-// To use the default Kingpin application, call AddFlags(kingpin.CommandLine)
-func AddFlags(a *kingpin.Application) *string {
-	return a.Flag(
-		"web.config.file",
-		"[EXPERIMENTAL] Path to configuration file that can enable TLS or authentication.",
-	).Default("").String()
+// To use the default Kingpin application, call
+// AddFlags(kingpin.CommandLine, ":portNum") where portNum is the default port.
+func AddFlags(a *kingpin.Application, defaultAddress string) *web.FlagConfig {
+	systemdSocket := func() *bool { b := false; return &b }() // Socket activation only available on Linux
+	if runtime.GOOS == "linux" {
+		systemdSocket = kingpin.Flag(
+			"web.systemd-socket",
+			"Use systemd socket activation listeners instead of port listeners (Linux only).",
+		).Bool()
+	}
+	flags := web.FlagConfig{
+		WebListenAddresses: a.Flag(
+			"web.listen-address",
+			"Addresses on which to expose metrics and web interface. Repeatable for multiple addresses.",
+		).Default(defaultAddress).Strings(),
+		WebSystemdSocket: systemdSocket,
+		WebConfigFile: a.Flag(
+			"web.config.file",
+			"[EXPERIMENTAL] Path to configuration file that can enable TLS or authentication.",
+		).Default("").String(),
+	}
+	return &flags
 }

web/tls_config.go

@@ -23,9 +23,11 @@ import (
 	"os"
 	"path/filepath"
 
+	"github.com/coreos/go-systemd/v22/activation"
 	"github.com/go-kit/log"
 	"github.com/go-kit/log/level"
 	config_util "github.com/prometheus/common/config"
+	"golang.org/x/sync/errgroup"
 	"gopkg.in/yaml.v2"
 )
 
@@ -51,6 +53,12 @@ type TLSConfig struct {
 	PreferServerCipherSuites bool       `yaml:"prefer_server_cipher_suites"`
 }
 
+type FlagConfig struct {
+	WebListenAddresses *[]string
+	WebSystemdSocket   *bool
+	WebConfigFile      *string
+}
+
 // SetDirectory joins any relative file paths with dir.
 func (t *TLSConfig) SetDirectory(dir string) {
 	t.TLSCertPath = config_util.JoinDir(dir, t.TLSCertPath)
@@ -177,22 +185,54 @@ func ConfigToTLSConfig(c *TLSConfig) (*tls.Config, error) {
 	return cfg, nil
 }
 
-// ListenAndServe starts the server on the given address. Based on the file
-// tlsConfigPath, TLS or basic auth could be enabled.
-func ListenAndServe(server *http.Server, tlsConfigPath string, logger log.Logger) error {
-	listener, err := net.Listen("tcp", server.Addr)
-	if err != nil {
-		return err
+// ServeMultiple starts the server on the given listeners. The FlagConfig is
+// also passed on to Serve.
+func ServeMultiple(listeners []net.Listener, server *http.Server, flags *FlagConfig, logger log.Logger) error {
+	errs := new(errgroup.Group)
+	for _, l := range listeners {
+		l := l
+		errs.Go(func() error {
+			return Serve(l, server, flags, logger)
+		})
+	}
+	return errs.Wait()
+}
+
+// ListenAndServe starts the server on addresses given in WebListenAddresses in
+// the FlagConfig or instead uses systemd socket activated listeners if
+// WebSystemdSocket in the FlagConfig is true. The FlagConfig is also passed on
+// to ServeMultiple.
+func ListenAndServe(server *http.Server, flags *FlagConfig, logger log.Logger) error {
+	if *flags.WebSystemdSocket {
+		level.Info(logger).Log("msg", "Listening on systemd activated listeners instead of port listeners.")
+		listeners, err := activation.Listeners()
+		if err != nil {
+			return err
+		}
+		if len(listeners) < 1 {
+			return errors.New("no socket activation file descriptors found")
+		}
+		return ServeMultiple(listeners, server, flags, logger)
 	}
-	defer listener.Close()
-	return Serve(listener, server, tlsConfigPath, logger)
+	listeners := make([]net.Listener, 0, len(*flags.WebListenAddresses))
+	for _, address := range *flags.WebListenAddresses {
+		listener, err := net.Listen("tcp", address)
+		if err != nil {
+			return err
+		}
+		defer listener.Close()
+		listeners = append(listeners, listener)
+	}
+	return ServeMultiple(listeners, server, flags, logger)
 }
 
-// Server starts the server on the given listener. Based on the file
-// tlsConfigPath, TLS or basic auth could be enabled.
-func Serve(l net.Listener, server *http.Server, tlsConfigPath string, logger log.Logger) error {
+// Server starts the server on the given listener. Based on the file path
+// WebConfigFile in the FlagConfig, TLS or basic auth could be enabled.
+func Serve(l net.Listener, server *http.Server, flags *FlagConfig, logger log.Logger) error {
+	level.Info(logger).Log("msg", "Listening on", "address", l.Addr().String())
+	tlsConfigPath := *flags.WebConfigFile
 	if tlsConfigPath == "" {
-		level.Info(logger).Log("msg", "TLS is disabled.", "http2", false)
+		level.Info(logger).Log("msg", "TLS is disabled.", "http2", false, "address", l.Addr().String())
 		return server.Serve(l)
 	}
 
@@ -225,10 +265,10 @@ func Serve(l net.Listener, server *http.Server, tlsConfigPath string, logger log
 			server.TLSNextProto = make(map[string]func(*http.Server, *tls.Conn, http.Handler))
 		}
 		// Valid TLS config.
-		level.Info(logger).Log("msg", "TLS is enabled.", "http2", c.HTTPConfig.HTTP2)
+		level.Info(logger).Log("msg", "TLS is enabled.", "http2", c.HTTPConfig.HTTP2, "address", l.Addr().String())
 	case errNoTLSConfig:
 		// No TLS config, back to plain HTTP.
-		level.Info(logger).Log("msg", "TLS is disabled.", "http2", false)
+		level.Info(logger).Log("msg", "TLS is disabled.", "http2", false, "address", l.Addr().String())
 		return server.Serve(l)
 	default:
 		// Invalid TLS config.
@@ -356,6 +396,6 @@ func (tv *TLSVersion) MarshalYAML() (interface{}, error) {
 // tlsConfigPath, TLS or basic auth could be enabled.
 //
 // Deprecated: Use ListenAndServe instead.
-func Listen(server *http.Server, tlsConfigPath string, logger log.Logger) error {
-	return ListenAndServe(server, tlsConfigPath, logger)
+func Listen(server *http.Server, flags *FlagConfig, logger log.Logger) error {
+	return ListenAndServe(server, flags, logger)
 }

web/tls_config_test.go

@@ -31,6 +31,14 @@ import (
 	"time"
 )
 
+// Helpers for literal FlagConfig
+func OfBool(i bool) *bool {
+	return &i
+}
+func OfString(i string) *string {
+	return &i
+}
+
 var (
 	port       = getPort()
 	testlogger = &testLogger{}
@@ -378,7 +386,12 @@ func TestConfigReloading(t *testing.T) {
 				recordConnectionError(errors.New("Panic starting server"))
 			}
 		}()
-		err := Listen(server, badYAMLPath, testlogger)
+		flagsBadYAMLPath := FlagConfig{
+			WebListenAddresses: &([]string{port}),
+			WebSystemdSocket:   OfBool(false),
+			WebConfigFile:      OfString(badYAMLPath),
+		}
+		err := Listen(server, &flagsBadYAMLPath, testlogger)
 		recordConnectionError(err)
 	}()
 
@@ -436,7 +449,6 @@ func (test *TestInputs) Test(t *testing.T) {
 	}()
 
 	server := &http.Server{
-		Addr: port,
 		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			w.Write([]byte("Hello World!"))
 		}),
@@ -448,7 +460,12 @@ func (test *TestInputs) Test(t *testing.T) {
 				recordConnectionError(errors.New("Panic starting server"))
 			}
 		}()
-		err := ListenAndServe(server, test.YAMLConfigPath, testlogger)
+		flags := FlagConfig{
+			WebListenAddresses: &([]string{port}),
+			WebSystemdSocket:   OfBool(false),
+			WebConfigFile:      &test.YAMLConfigPath,
+		}
+		err := ListenAndServe(server, &flags, testlogger)
 		recordConnectionError(err)
 	}()