Feature: Add Prometheus exporter (#505)

cmd/root.go

@@ -9,6 +9,7 @@ import (
 	"github.com/axllent/mailpit/config"
 	"github.com/axllent/mailpit/internal/auth"
 	"github.com/axllent/mailpit/internal/logger"
+	"github.com/axllent/mailpit/internal/prometheus"
 	"github.com/axllent/mailpit/internal/smtpd"
 	"github.com/axllent/mailpit/internal/smtpd/chaos"
 	"github.com/axllent/mailpit/internal/storage"
@@ -39,6 +40,14 @@ Documentation:
 			os.Exit(1)
 		}
 
+		// Start Prometheus metrics if enabled
+		switch prometheus.GetMode() {
+		case "integrated":
+			prometheus.StartUpdater()
+		case "separate":
+			go prometheus.StartSeparateServer()
+		}
+
 		go server.Listen()
 
 		if err := smtpd.Listen(); err != nil {
@@ -112,6 +121,9 @@ func init() {
 	rootCmd.Flags().StringVar(&config.SendAPIAuthFile, "send-api-auth-file", config.SendAPIAuthFile, "A password file for Send API authentication")
 	rootCmd.Flags().BoolVar(&config.SendAPIAuthAcceptAny, "send-api-auth-accept-any", config.SendAPIAuthAcceptAny, "Accept any username and password for the Send API endpoint, including none")
 
+	// Prometheus Metrics
+	rootCmd.Flags().StringVar(&config.PrometheusListen, "enable-prometheus", config.PrometheusListen, "Enable Prometheus metrics: false=disabled, 'true'=use web port, address=separate server (':9090')")
+
 	// SMTP server
 	rootCmd.Flags().StringVarP(&config.SMTPListen, "smtp", "s", config.SMTPListen, "SMTP bind interface and port")
 	rootCmd.Flags().StringVar(&config.SMTPAuthFile, "smtp-auth-file", config.SMTPAuthFile, "A password file for SMTP authentication")
@@ -262,6 +274,11 @@ func initConfigFromEnv() {
 		config.SendAPIAuthAcceptAny = true
 	}
 
+	// Prometheus Metrics
+	if len(os.Getenv("MP_ENABLE_PROMETHEUS")) > 0 {
+		config.PrometheusListen = os.Getenv("MP_ENABLE_PROMETHEUS")
+	}
+
 	// SMTP server
 	if len(os.Getenv("MP_SMTP_BIND_ADDR")) > 0 {
 		config.SMTPListen = os.Getenv("MP_SMTP_BIND_ADDR")

config/config.go

@@ -191,6 +191,10 @@ var (
 	// AllowUntrustedTLS allows untrusted HTTPS connections link checking & screenshot generation
 	AllowUntrustedTLS bool
 
+	// PrometheusListen address for Prometheus metrics server
+	// Empty = disabled, "true"= use existing web server, address = separate server
+	PrometheusListen string
+
 	// Version is the default application version, updated on release
 	Version = "dev"
 
@@ -567,5 +571,17 @@ func VerifyConfig() error {
 		logger.Log().Info("demo mode enabled")
 	}
 
+	// Prometheus configuration validation
+	if PrometheusListen != "" {
+		mode := strings.ToLower(strings.TrimSpace(PrometheusListen))
+		if mode != "true" && mode != "false" {
+			// Validate as address for separate server mode
+			_, err := net.ResolveTCPAddr("tcp", PrometheusListen)
+			if err != nil {
+				return fmt.Errorf("[prometheus] %s", err.Error())
+			}
+		}
+	}
+
 	return nil
 }

go.mod

@@ -21,6 +21,7 @@ require (
 	github.com/leporo/sqlf v1.4.0
 	github.com/lithammer/shortuuid/v4 v4.2.0
 	github.com/mneis/go-telnet v0.0.0-20221017141824-6f643e477c62
+	github.com/prometheus/client_golang v1.22.0
 	github.com/rqlite/gorqlite v0.0.0-20250128004930-114c7828b55a
 	github.com/sirupsen/logrus v1.9.3
 	github.com/spf13/cobra v1.9.1
@@ -36,7 +37,9 @@ require (
 require (
 	github.com/GehirnInc/crypt v0.0.0-20230320061759-8cc1b52080c5 // indirect
 	github.com/andybalholm/cascadia v1.3.3 // indirect
+	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cention-sany/utf7 v0.0.0-20170124080048-26cad61bd60a // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/gogs/chardet v0.0.0-20211120154057-b7413eaefb8f // indirect
 	github.com/google/uuid v1.6.0 // indirect
@@ -45,9 +48,13 @@ require (
 	github.com/jaytaylor/html2text v0.0.0-20230321000545-74c2419ad056 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/mattn/go-runewidth v0.0.16 // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/ncruces/go-strftime v0.1.9 // indirect
 	github.com/olekukonko/tablewriter v1.0.6 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
+	github.com/prometheus/client_model v0.6.1 // indirect
+	github.com/prometheus/common v0.62.0 // indirect
+	github.com/prometheus/procfs v0.15.1 // indirect
 	github.com/reiver/go-oi v1.0.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
@@ -58,6 +65,7 @@ require (
 	golang.org/x/exp v0.0.0-20250506013437-ce4c2cf36ca6 // indirect
 	golang.org/x/image v0.27.0 // indirect
 	golang.org/x/sys v0.33.0 // indirect
+	google.golang.org/protobuf v1.36.5 // indirect
 	modernc.org/libc v1.65.8 // indirect
 	modernc.org/mathutil v1.7.1 // indirect
 	modernc.org/memory v1.11.0 // indirect

go.sum

@@ -8,8 +8,12 @@ github.com/araddon/dateparse v0.0.0-20210429162001-6b43995a97de h1:FxWPpzIjnTlhP
 github.com/araddon/dateparse v0.0.0-20210429162001-6b43995a97de/go.mod h1:DCaWoUhZrYW9p1lxo/cm8EmUOOzAPSEZNGF2DK1dJgw=
 github.com/axllent/semver v0.0.1 h1:QqF+KSGxgj8QZzSXAvKFqjGWE5792ksOnQhludToK8E=
 github.com/axllent/semver v0.0.1/go.mod h1:2xSPzvG8n9mRfdtxSvWvfTfQGWfHsMsHO1iZnKATMSc=
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
 github.com/cention-sany/utf7 v0.0.0-20170124080048-26cad61bd60a h1:MISbI8sU/PSK/ztvmWKFcI7UGb5/HQT7B+i3a2myKgI=
 github.com/cention-sany/utf7 v0.0.0-20170124080048-26cad61bd60a/go.mod h1:2GxOXOlEPAMFPfp014mK1SWq8G8BN8o7/dfYqJrVGn8=
+github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
 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=
@@ -25,6 +29,8 @@ github.com/gogs/chardet v0.0.0-20211120154057-b7413eaefb8f/go.mod h1:Pcatq5tYkCW
 github.com/gomarkdown/markdown v0.0.0-20250311123330-531bef5e742b h1:EY/KpStFl60qA17CptGXhwfZ+k1sFNJIUNR8DdbcuUk=
 github.com/gomarkdown/markdown v0.0.0-20250311123330-531bef5e742b/go.mod h1:JDGcbDT52eL4fju3sZ4TeHGsQwhG9nbDV21aMyhwPoA=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
+github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
 github.com/google/pprof v0.0.0-20250317173921-a4b03ec1a45e h1:ijClszYn+mADRFY17kjQEVQ1XRhq2/JR1M3sGqeJoxs=
 github.com/google/pprof v0.0.0-20250317173921-a4b03ec1a45e/go.mod h1:boTsfXsheKC2y+lKOCMpSfarhxDeIzfZG1jqGcPl3cA=
 github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
@@ -45,6 +51,8 @@ github.com/klauspost/compress v1.18.0 h1:c/Cqfb0r+Yi+JtIEq73FWXVkRonBlf0CRNYc8Zt
 github.com/klauspost/compress v1.18.0/go.mod h1:2Pp+KzxcywXVXMr50+X0Q/Lsb43OQHYWRCY2AiWywWQ=
 github.com/kovidgoyal/imaging v1.6.4 h1:K0idhRPXnRrJBKnBYcTfI1HTWSNDeAn7hYDvf9I0dCk=
 github.com/kovidgoyal/imaging v1.6.4/go.mod h1:bEIgsaZmXlvFfkv/CUxr9rJook6AQkJnpB5EPosRfRY=
+github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=
+github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
 github.com/leporo/sqlf v1.4.0 h1:SyWnX/8GSGOzVmanG0Ub1c04mR9nNl6Tq3IeFKX2/4c=
 github.com/leporo/sqlf v1.4.0/go.mod h1:pgN9yKsAnQ+2ewhbZogr98RcasUjPsHF3oXwPPhHvBw=
 github.com/lithammer/shortuuid/v4 v4.2.0 h1:LMFOzVB3996a7b8aBuEXxqOBflbfPQAiVzkIcHO0h8c=
@@ -59,6 +67,8 @@ github.com/mattn/go-sqlite3 v1.14.16 h1:yOQRA0RpS5PFz/oikGwBEqvAWhWg5ufRz4ETLjwp
 github.com/mattn/go-sqlite3 v1.14.16/go.mod h1:2eHXhiwb8IkHr+BDWZGa96P6+rkvnG63S2DGjv9HUNg=
 github.com/mneis/go-telnet v0.0.0-20221017141824-6f643e477c62 h1:XMG5DklHoioVYysfYglOB7vRBg/LOUJZy2mq2QyedLg=
 github.com/mneis/go-telnet v0.0.0-20221017141824-6f643e477c62/go.mod h1:niAM5cni0I/47IFA995xQfeK58Mkbb7FHJjacY4OGQg=
+github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
+github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
 github.com/ncruces/go-strftime v0.1.9 h1:bY0MQC28UADQmHmaF5dgpLmImcShSi2kHU9XLdhx/f4=
 github.com/ncruces/go-strftime v0.1.9/go.mod h1:Fwc5htZGVVkseilnfgOVb9mKy6w1naJmn9CehxcKcls=
 github.com/olekukonko/tablewriter v0.0.5 h1:P2Ga83D34wi1o9J6Wh1mRuqd4mF/x/lgBS7N7AbDhec=
@@ -67,6 +77,14 @@ github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/prometheus/client_golang v1.22.0 h1:rb93p9lokFEsctTys46VnV1kLCDpVZ0a/Y92Vm0Zc6Q=
+github.com/prometheus/client_golang v1.22.0/go.mod h1:R7ljNsLXhuQXYZYtw6GAE9AZg8Y7vEW5scdCXrWRXC0=
+github.com/prometheus/client_model v0.6.1 h1:ZKSh/rekM+n3CeS952MLRAdFwIKqeY8b62p8ais2e9E=
+github.com/prometheus/client_model v0.6.1/go.mod h1:OrxVMOVHjw3lKMa8+x6HeMGkHMQyHDk9E3jmP2AmGiY=
+github.com/prometheus/common v0.62.0 h1:xasJaQlnWAeyHdUBeGjXmutelfJHWMRr+Fg4QszZ2Io=
+github.com/prometheus/common v0.62.0/go.mod h1:vyBcEuLSvWos9B1+CyL7JZ2up+uFzXhkqml0W5zIY1I=
+github.com/prometheus/procfs v0.15.1 h1:YagwOFzUgYfKKHX6Dr+sHT7km/hxC76UB0learggepc=
+github.com/prometheus/procfs v0.15.1/go.mod h1:fB45yRUv8NstnjriLhBQLuOUt+WW4BsoGhij/e3PBqk=
 github.com/reiver/go-oi v1.0.0 h1:nvECWD7LF+vOs8leNGV/ww+F2iZKf3EYjYZ527turzM=
 github.com/reiver/go-oi v1.0.0/go.mod h1:RrDBct90BAhoDTxB1fenZwfykqeGvhI6LsNfStJoEkI=
 github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
@@ -190,6 +208,8 @@ golang.org/x/tools v0.21.1-0.20240508182429-e35e4ccd0d2d/go.mod h1:aiJjzUbINMkxb
 golang.org/x/tools v0.33.0 h1:4qz2S3zmRxbGIhDIAgjxvFutSvH5EfnsYrRBj0UI0bc=
 golang.org/x/tools v0.33.0/go.mod h1:CIJMaWEY88juyUfo7UbgPqbC8rU2OqfAV1h2Qp0oMYI=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/protobuf v1.36.5 h1:tPhr+woSbjfYvY6/GPufUoYizxw1cF/yFoxJ2fmpwlM=
+google.golang.org/protobuf v1.36.5/go.mod h1:9fA7Ob0pmnwhb644+1+CVWFRbNajQ6iRojtC/QF5bRE=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

internal/prometheus/metrics.go

@@ -0,0 +1,188 @@
+// Package prometheus provides Prometheus metrics for Mailpit
+package prometheus
+
+import (
+	"net/http"
+	"strings"
+	"time"
+
+	"github.com/axllent/mailpit/config"
+	"github.com/axllent/mailpit/internal/logger"
+	"github.com/axllent/mailpit/internal/stats"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+var (
+	// Registry is the Prometheus registry for Mailpit metrics
+	Registry = prometheus.NewRegistry()
+
+	// Metrics
+	totalMessages    prometheus.Gauge
+	unreadMessages   prometheus.Gauge
+	databaseSize     prometheus.Gauge
+	messagesDeleted  prometheus.Counter
+	smtpAccepted     prometheus.Counter
+	smtpRejected     prometheus.Counter
+	smtpIgnored      prometheus.Counter
+	smtpAcceptedSize prometheus.Counter
+	uptime           prometheus.Gauge
+	memoryUsage      prometheus.Gauge
+	tagCounters      *prometheus.GaugeVec
+)
+
+// InitMetrics initializes all Prometheus metrics
+func InitMetrics() {
+	// Create metrics
+	totalMessages = prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "mailpit_messages",
+		Help: "Total number of messages in the database",
+	})
+
+	unreadMessages = prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "mailpit_messages_unread",
+		Help: "Number of unread messages in the database",
+	})
+
+	databaseSize = prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "mailpit_database_size_bytes",
+		Help: "Size of the database in bytes",
+	})
+
+	messagesDeleted = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "mailpit_messages_deleted_total",
+		Help: "Total number of messages deleted",
+	})
+
+	smtpAccepted = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "mailpit_smtp_accepted_total",
+		Help: "Total number of SMTP messages accepted",
+	})
+
+	smtpRejected = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "mailpit_smtp_rejected_total",
+		Help: "Total number of SMTP messages rejected",
+	})
+
+	smtpIgnored = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "mailpit_smtp_ignored_total",
+		Help: "Total number of SMTP messages ignored (duplicates)",
+	})
+
+	smtpAcceptedSize = prometheus.NewCounter(prometheus.CounterOpts{
+		Name: "mailpit_smtp_accepted_size_bytes_total",
+		Help: "Total size of accepted SMTP messages in bytes",
+	})
+
+	uptime = prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "mailpit_uptime_seconds",
+		Help: "Uptime of Mailpit in seconds",
+	})
+
+	memoryUsage = prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "mailpit_memory_usage_bytes",
+		Help: "Memory usage in bytes",
+	})
+
+	tagCounters = prometheus.NewGaugeVec(
+		prometheus.GaugeOpts{
+			Name: "mailpit_tag_messages",
+			Help: "Number of messages per tag",
+		},
+		[]string{"tag"},
+	)
+
+	// Register metrics
+	Registry.MustRegister(totalMessages)
+	Registry.MustRegister(unreadMessages)
+	Registry.MustRegister(databaseSize)
+	Registry.MustRegister(messagesDeleted)
+	Registry.MustRegister(smtpAccepted)
+	Registry.MustRegister(smtpRejected)
+	Registry.MustRegister(smtpIgnored)
+	Registry.MustRegister(smtpAcceptedSize)
+	Registry.MustRegister(uptime)
+	Registry.MustRegister(memoryUsage)
+	Registry.MustRegister(tagCounters)
+}
+
+// UpdateMetrics updates all metrics with current values
+func UpdateMetrics() {
+	info := stats.Load()
+
+	totalMessages.Set(float64(info.Messages))
+	unreadMessages.Set(float64(info.Unread))
+	databaseSize.Set(float64(info.DatabaseSize))
+	messagesDeleted.Add(float64(info.RuntimeStats.MessagesDeleted))
+	smtpAccepted.Add(float64(info.RuntimeStats.SMTPAccepted))
+	smtpRejected.Add(float64(info.RuntimeStats.SMTPRejected))
+	smtpIgnored.Add(float64(info.RuntimeStats.SMTPIgnored))
+	smtpAcceptedSize.Add(float64(info.RuntimeStats.SMTPAcceptedSize))
+	uptime.Set(float64(info.RuntimeStats.Uptime))
+	memoryUsage.Set(float64(info.RuntimeStats.Memory))
+
+	// Reset tag counters
+	tagCounters.Reset()
+
+	// Update tag counters
+	for tag, count := range info.Tags {
+		tagCounters.WithLabelValues(tag).Set(float64(count))
+	}
+}
+
+// Returns the Prometheus handler & disables double compression in middleware
+func GetHandler() http.Handler {
+	return promhttp.HandlerFor(Registry, promhttp.HandlerOpts{
+		DisableCompression: true,
+	})
+}
+
+// StartUpdater starts the periodic metrics update routine
+func StartUpdater() {
+	InitMetrics()
+	UpdateMetrics()
+
+	// Start periodic updates
+	go func() {
+		ticker := time.NewTicker(15 * time.Second)
+		defer ticker.Stop()
+
+		for range ticker.C {
+			UpdateMetrics()
+		}
+	}()
+}
+
+// StartSeparateServer starts a separate HTTP server for Prometheus metrics
+func StartSeparateServer() {
+	StartUpdater()
+
+	logger.Log().Infof("[prometheus] metrics server listening on %s", config.PrometheusListen)
+
+	// Create a dedicated mux for the metrics server
+	mux := http.NewServeMux()
+	mux.Handle("/metrics", promhttp.HandlerFor(Registry, promhttp.HandlerOpts{}))
+
+	// Create a dedicated server instance
+	server := &http.Server{
+		Addr:    config.PrometheusListen,
+		Handler: mux,
+	}
+
+	// Start HTTP server
+	if err := server.ListenAndServe(); err != nil {
+		logger.Log().Errorf("[prometheus] metrics server error: %s", err.Error())
+	}
+}
+
+// GetMode returns the Prometheus run mode
+func GetMode() string {
+	mode := strings.ToLower(strings.TrimSpace(config.PrometheusListen))
+	if mode == "false" {
+		return "disabled"
+	}
+	if mode == "true" {
+		return "integrated"
+	}
+	return "separate"
+}

server/server.go

@@ -19,6 +19,7 @@ import (
 	"github.com/axllent/mailpit/internal/auth"
 	"github.com/axllent/mailpit/internal/logger"
 	"github.com/axllent/mailpit/internal/pop3"
+	"github.com/axllent/mailpit/internal/prometheus"
 	"github.com/axllent/mailpit/internal/stats"
 	"github.com/axllent/mailpit/internal/storage"
 	"github.com/axllent/mailpit/internal/tools"
@@ -182,6 +183,13 @@ func apiRoutes() *mux.Router {
 	r.HandleFunc(config.Webroot+"api/v1/chaos", middleWareFunc(apiv1.GetChaos)).Methods("GET")
 	r.HandleFunc(config.Webroot+"api/v1/chaos", middleWareFunc(apiv1.SetChaos)).Methods("PUT")
 
+	// Prometheus metrics (if enabled and using existing server)
+	if prometheus.GetMode() == "integrated" {
+		r.HandleFunc(config.Webroot+"metrics", middleWareFunc(func(w http.ResponseWriter, r *http.Request) {
+			prometheus.GetHandler().ServeHTTP(w, r)
+		})).Methods("GET")
+	}
+
 	// web UI websocket
 	r.HandleFunc(config.Webroot+"api/events", apiWebsocket).Methods("GET")