diff --git a/api.go b/api.go
index 8cd4909..6b6fc52 100644
--- a/api.go
+++ b/api.go
@@ -18,7 +18,7 @@ func main() {
 	mux.Get("/", http.HandlerFunc(handlers.NewSession))
 	mux.Get("/sessions/:sessionId", http.HandlerFunc(handlers.GetSession))
 	mux.Post("/sessions/:sessionId/instances", http.HandlerFunc(handlers.NewInstance))
-	mux.Delete("/sessions/:sessionId/instances/:instanceId", http.HandlerFunc(handlers.DeleteInstance))
+	mux.Delete("/sessions/:sessionId/instances/:instanceName", http.HandlerFunc(handlers.DeleteInstance))
 
 	h := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		http.ServeFile(w, r, "./www/index.html")
@@ -26,7 +26,7 @@ func main() {
 	mux.Get("/p/:sessionId", h)
 	mux.Get("/assets/*", http.FileServer(http.Dir("./www")))
 
-	mux.Get("/sessions/:sessionId/instances/:instanceId/attach", websocket.Handler(handlers.Exec))
+	mux.Get("/sessions/:sessionId/instances/:instanceName/attach", websocket.Handler(handlers.Exec))
 
 	n := negroni.Classic()
 	n.UseHandler(mux)
diff --git a/handlers/delete_instance.go b/handlers/delete_instance.go
index 42ed695..393fcce 100644
--- a/handlers/delete_instance.go
+++ b/handlers/delete_instance.go
@@ -9,10 +9,10 @@ import (
 
 func DeleteInstance(rw http.ResponseWriter, req *http.Request) {
 	sessionId := bone.GetValue(req, "sessionId")
-	instanceId := bone.GetValue(req, "instanceId")
+	instanceName := bone.GetValue(req, "instanceName")
 
 	s := services.GetSession(sessionId)
-	i := services.GetInstance(s, instanceId)
+	i := services.GetInstance(s, instanceName)
 	err := services.DeleteInstance(s, i)
 	if err != nil {
 		rw.WriteHeader(http.StatusInternalServerError)
diff --git a/handlers/exec.go b/handlers/exec.go
index 40f4ad7..3265feb 100644
--- a/handlers/exec.go
+++ b/handlers/exec.go
@@ -15,12 +15,12 @@ import (
 // Echo the data received on the WebSocket.
 func Exec(ws *websocket.Conn) {
 	sessionId := bone.GetValue(ws.Request(), "sessionId")
-	instanceId := bone.GetValue(ws.Request(), "instanceId")
+	instanceName := bone.GetValue(ws.Request(), "instanceName")
 
 	ctx := context.Background()
 
 	session := services.GetSession(sessionId)
-	instance := services.GetInstance(session, instanceId)
+	instance := services.GetInstance(session, instanceName)
 
 	if instance.Stdout == nil {
 		id, err := services.CreateExecConnection(instance.Name, ctx)
diff --git a/handlers/new_instance.go b/handlers/new_instance.go
index 5cfa7ee..e346a27 100644
--- a/handlers/new_instance.go
+++ b/handlers/new_instance.go
@@ -14,12 +14,14 @@ func NewInstance(rw http.ResponseWriter, req *http.Request) {
 
 	s := services.GetSession(sessionId)
 
+	s.Lock()
 	if len(s.Instances) >= 5 {
 		rw.WriteHeader(http.StatusConflict)
 		return
 	}
 
 	i, err := services.NewInstance(s)
+	s.Unlock()
 	if err != nil {
 		log.Println(err)
 		//TODO: Set a status error
diff --git a/services/instance.go b/services/instance.go
index e95b8e2..8635c87 100644
--- a/services/instance.go
+++ b/services/instance.go
@@ -7,20 +7,17 @@ import (
 	"github.com/franela/play-with-docker/types"
 )
 
-var instances map[string]map[string]*types.Instance
-
 var dindImage string
 var defaultDindImageName string
 
 func init() {
-	instances = make(map[string]map[string]*types.Instance)
-        dindImage = getDindImageName()
+	dindImage = getDindImageName()
 }
 
 func getDindImageName() string {
 	dindImage := os.Getenv("DIND_IMAGE")
-        defaultDindImageName = "docker:1.12.2-rc2-dind"
-        if len(dindImage) == 0 {
+	defaultDindImageName = "docker:1.12.2-rc2-dind"
+	if len(dindImage) == 0 {
 		dindImage = defaultDindImageName
 	}
 	return dindImage
@@ -37,21 +34,20 @@ func NewInstance(session *types.Session) (*types.Instance, error) {
 		return nil, err
 	}
 
-	if instances[session.Id] == nil {
-		instances[session.Id] = make(map[string]*types.Instance)
+	if session.Instances == nil {
+		session.Instances = make(map[string]*types.Instance)
 	}
-	instances[session.Id][instance.Name] = instance
+	session.Instances[instance.Name] = instance
 
 	return instance, nil
 }
 
-func GetInstance(session *types.Session, instanceId string) *types.Instance {
+func GetInstance(session *types.Session, name string) *types.Instance {
 	//TODO: Use redis
-	i := instances[session.Id][instanceId]
-	return i
+	return session.Instances[name]
 }
 func DeleteInstance(session *types.Session, instance *types.Instance) error {
 	//TODO: Use redis
-	delete(instances[session.Id], instance.Name)
+	delete(session.Instances, instance.Name)
 	return DeleteContainer(instance.Name)
 }
diff --git a/services/session.go b/services/session.go
index 6f82613..7eca586 100644
--- a/services/session.go
+++ b/services/session.go
@@ -49,11 +49,5 @@ func NewSession() (*types.Session, error) {
 
 func GetSession(sessionId string) *types.Session {
 	//TODO: Use redis
-	s, found := sessions[sessionId]
-	if found {
-		s.Instances = instances[sessionId]
-		return s
-	} else {
-		return nil
-	}
+	return sessions[sessionId]
 }
diff --git a/types/session.go b/types/session.go
index 61cb120..38af7fc 100644
--- a/types/session.go
+++ b/types/session.go
@@ -1,11 +1,14 @@
 package types
 
 import (
+	"sync"
+
 	"github.com/docker/docker/api/types"
 	"github.com/franela/play-with-docker/cookoo"
 )
 
 type Session struct {
+	sync.Mutex
 	Id        string               `json:"id"`
 	Instances map[string]*Instance `json:"instances"`
 }