Add support for setting alias when creatign instance. (#140)

* Add support for setting alias when creatign instance.

The POST to create a instance now provides an `alias` field which
then can be used to access the instance services through the following
URL:

`http://<alias>-<short_session>-<port>.<tld>`

When creating a session you can now send an `alias`

* Remove unnecessary function

* Add alias support for DNS resolution

handlers/reverseproxy.go

@@ -11,11 +11,14 @@ import (
 
 	"github.com/gorilla/mux"
 	"github.com/play-with-docker/play-with-docker/config"
+	"github.com/play-with-docker/play-with-docker/services"
 )
 
 func getTargetInfo(vars map[string]string, req *http.Request) (string, string) {
 	node := vars["node"]
 	port := vars["port"]
+	alias := vars["alias"]
+	sessionPrefix := vars["session"]
 	hostPort := strings.Split(req.Host, ":")
 
 	// give priority to the URL host port
@@ -25,6 +28,14 @@ func getTargetInfo(vars map[string]string, req *http.Request) (string, string) {
 		port = "80"
 	}
 
+	if alias != "" {
+		instance := services.FindInstanceByAlias(sessionPrefix, alias)
+		if instance != nil {
+			node = instance.IP
+			return node, port
+		}
+	}
+
 	if strings.HasPrefix(node, "pwd") {
 		// Node is actually an ip, need to convert underscores by dots.
 		ip := strings.Replace(strings.TrimPrefix(node, "pwd"), "_", ".", -1)