Add metrics (#70)

* Add prometheus support to count sessions, instances and clientes over
time

* Track counters on server reload

* Change to gauges

api.go

@@ -12,6 +12,7 @@ import (
 	"github.com/franela/play-with-docker/services"
 	"github.com/franela/play-with-docker/templates"
 	"github.com/gorilla/mux"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"github.com/urfave/negroni"
 )
 
@@ -71,6 +72,7 @@ func main() {
 	}))
 
 	r.Handle("/sessions/{sessionId}/ws/", server)
+	r.Handle("/metrics", promhttp.Handler())
 
 	n := negroni.Classic()
 	n.UseHandler(r)

services/client.go

@@ -4,8 +4,20 @@ import (
 	"log"
 
 	"github.com/googollee/go-socket.io"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
+var (
+	clientsGauge = prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "clients",
+		Help: "Clients",
+	})
+)
+
+func init() {
+	prometheus.MustRegister(clientsGauge)
+}
+
 type ViewPort struct {
 	Rows uint
 	Cols uint
@@ -23,6 +35,7 @@ func (c *Client) ResizeViewPort(cols, rows uint) {
 }
 
 func NewClient(so socketio.Socket, session *Session) *Client {
+	clientsGauge.Inc()
 	so.Join(session.Id)
 
 	c := &Client{so: so, Id: so.Id()}
@@ -52,7 +65,9 @@ func NewClient(so socketio.Socket, session *Session) *Client {
 			}
 		}
 	})
+
 	so.On("disconnection", func() {
+		clientsGauge.Dec()
 		// Client has disconnected. Remove from session and recheck terminal sizes.
 		for i, cl := range session.clients {
 			if cl.Id == c.Id {
@@ -69,6 +84,5 @@ func NewClient(so socketio.Socket, session *Session) *Client {
 			}
 		}
 	})
-
 	return c
 }

services/instance.go

@@ -11,10 +11,22 @@ import (
 
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/client"
+	"github.com/prometheus/client_golang/prometheus"
 )
 
 var rw sync.Mutex
 
+var (
+	instancesGauge = prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "instances",
+		Help: "Instances",
+	})
+)
+
+func init() {
+	prometheus.MustRegister(instancesGauge)
+}
+
 type Instance struct {
 	session      *Session                `json:"-"`
 	Name         string                  `json:"name"`
@@ -90,6 +102,8 @@ func NewInstance(session *Session) (*Instance, error) {
 
 	wsServer.BroadcastTo(session.Id, "new instance", instance.Name, instance.IP, instance.Hostname)
 
+	instancesGauge.Inc()
+
 	return instance, nil
 }
 
@@ -142,5 +156,7 @@ func DeleteInstance(session *Session, instance *Instance) error {
 
 	wsServer.BroadcastTo(session.Id, "delete instance", instance.Name)
 
+	instancesGauge.Dec()
+
 	return err
 }

services/session.go

@@ -14,9 +14,21 @@ import (
 
 	"github.com/docker/docker/client"
 	"github.com/googollee/go-socket.io"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/twinj/uuid"
 )
 
+var (
+	sessionsGauge = prometheus.NewGauge(prometheus.GaugeOpts{
+		Name: "sessions",
+		Help: "Sessions",
+	})
+)
+
+func init() {
+	prometheus.MustRegister(sessionsGauge)
+}
+
 var wsServer *socketio.Server
 
 type Session struct {
@@ -129,10 +141,15 @@ func CloseSession(s *Session) error {
 	s.rw.Lock()
 	defer s.rw.Unlock()
 
+	sessionsGauge.Dec()
 	if s.ticker != nil {
 		s.ticker.Stop()
 	}
 	wsServer.BroadcastTo(s.Id, "session end")
+	for _, c := range s.clients {
+		c.so.Emit("disconnect")
+		clientsGauge.Dec()
+	}
 	log.Printf("Starting clean up of session [%s]\n", s.Id)
 	for _, i := range s.Instances {
 		if i.conn != nil {
@@ -207,6 +224,8 @@ func NewSession() (*Session, error) {
 	if err := saveSessionsToDisk(); err != nil {
 		return nil, err
 	}
+
+	sessionsGauge.Inc()
 	return s, nil
 }
 
@@ -236,6 +255,7 @@ func LoadSessionsFromDisk() error {
 
 		// schedule session expiration
 		for _, s := range sessions {
+			sessionsGauge.Inc()
 			timeLeft := s.ExpiresAt.Sub(time.Now())
 			CloseSessionAfter(s, timeLeft)
 
@@ -243,7 +263,7 @@ func LoadSessionsFromDisk() error {
 			for _, i := range s.Instances {
 				// wire the session back to the instance
 				i.session = s
-
+				instancesGauge.Inc()
 			}
 
 			// Connect PWD daemon to the new network