App Engine: Go - Latency - google-app-engine

Question

Hi I Made a simple photo blog app with go and when I deployed it to App Engine it had issues updating the pictures on the home page. When i upload a picture and go back to the home page, it take a few refreshes to show the image. https://hello-world-170523.appspot.com/.
login info:
email: test#example.com
password: test
This is the source code:
package main
import (
"fmt"
"html/template"
"io"
"net/http"
"os"
"path/filepath"
"strings"
"google.golang.org/appengine"
"github.com/gorilla/sessions"
)
type IndexPage struct {
Photos []string
LogedIn bool
}
type LoginPage struct {
Body string
FirstName string
LastName string
Email string
Error string
}
type UploadPage struct {
Error string
Msg string
}
func getPhotos() []string {
photos := make([]string, 0)
filepath.Walk("assets/img", func(path string, fi os.FileInfo, err error) error {
if fi.IsDir() {
return nil
}
path = strings.Replace(path, "\\", "/", -1)
photos = append(photos, path)
return nil
})
return photos
}
var store = sessions.NewCookieStore([]byte("HelloWorld"))
func loginPage(res http.ResponseWriter, req *http.Request) {
loginError := ""
session, _ := store.Get(req, "session")
str, _ := session.Values["logged-in"].(string)
if str == "YES" {
http.Redirect(res, req, "/admin", 302)
return
}
if req.Method == "POST" {
email := req.FormValue("email")
password := req.FormValue("password")
if email == "test#example.com" && password == "test" {
session.Values["logged-in"] = "YES"
session.Save(req, res)
http.Redirect(res, req, "/admin", 302)
return
} else {
loginError = "Invalid Credential. Please Resubmit"
}
}
tpl, err := template.ParseFiles("assets/tpl/login.gohtml", "assets/tpl/header.gohtml")
if err != nil {
http.Error(res, err.Error(), 500)
return
}
err = tpl.Execute(res, LoginPage{
Error: loginError,
})
}
func admin(res http.ResponseWriter, req *http.Request) {
uploadError := ""
successMsg := ""
session, _ := store.Get(req, "session")
str, _ := session.Values["logged-in"].(string)
if str != "YES" {
http.Redirect(res, req, "/login", 302)
return
}
if req.Method == "POST" {
// <input type="file" name="file">
src, hdr, err := req.FormFile("file")
if err != nil {
http.Error(res, "Invalid File.", 500)
return
}
defer src.Close()
// create a new file
// make sure you have a "tmp" directory in your web root
dst, err := os.Create("assets/img/" + hdr.Filename)
if err != nil {
http.Error(res, err.Error(), 500)
return
}
defer dst.Close()
// copy the uploaded file into the new file
io.Copy(dst, src)
}
tpl, err := template.ParseFiles("assets/tpl/admin.gohtml", "assets/tpl/header.gohtml")
if err != nil {
http.Error(res, err.Error(), 500)
return
}
err = tpl.Execute(res, UploadPage{
Error: uploadError,
Msg: successMsg,
})
if err != nil {
http.Error(res, err.Error(), 500)
}
}
func index(res http.ResponseWriter, req *http.Request) {
session, _ := store.Get(req, "session")
str, _ := session.Values["logged-in"].(string)
logged := false
if str == "YES" {
logged = true
}
tpl, err := template.ParseFiles("assets/tpl/index.gohtml", "assets/tpl/header.gohtml")
if err != nil {
fmt.Println(err)
http.Error(res, err.Error(), 500)
return
}
err = tpl.Execute(res, IndexPage{
Photos: getPhotos(),
LogedIn: logged,
})
if err != nil {
fmt.Println(err)
http.Error(res, err.Error(), 500)
}
}
func logout(res http.ResponseWriter, req *http.Request) {
session, _ := store.Get(req, "session")
str, _ := session.Values["logged-in"].(string)
if str == "YES" {
delete(session.Values, "logged-in")
session.Save(req, res)
http.Redirect(res, req, "/", 302)
} else {
http.Redirect(res, req, "/login", 302)
}
}
func deletePic(res http.ResponseWriter, req *http.Request) {
session, _ := store.Get(req, "session")
str, _ := session.Values["logged-in"].(string)
if str != "YES" {
http.Redirect(res, req, "/", 302)
return
}
if req.Method == "POST" {
imgName := req.FormValue("imgName")
err := os.Remove(imgName)
if err != nil {
http.Error(res, err.Error(), 500)
}
}
tpl, err := template.ParseFiles("assets/tpl/delete.gohtml", "assets/tpl/header.gohtml")
if err != nil {
http.Error(res, err.Error(), 500)
}
err = tpl.Execute(res, IndexPage{
Photos: getPhotos(),
})
if err != nil {
http.Error(res, err.Error(), 500)
}
}
func main() {
http.HandleFunc("/delete", deletePic)
http.Handle("/assets/", http.StripPrefix("/assets", http.FileServer(http.Dir("./assets"))))
http.HandleFunc("/", index)
http.HandleFunc("/admin", admin)
http.HandleFunc("/login", loginPage)
http.HandleFunc("/logout", logout)
appengine.Main()
}
And my app.yaml:
runtime: go
env: flex