Why does a Go app crash on VPS but work locally?

Question

go

Tell me, I made a simple go application, several html templates and data output from mongodb.
Brief content of Main:

func main() {
  session, err := mgo.Dial("mongodb://127.0.0.1")
  if err != nil {
    fmt.Println(err)
  }
  defer session.Close()
  http.Handle("/layout/", http.StripPrefix("/layout/", http.FileServer(http.Dir("templates/layout"))))
  http.HandleFunc("/login", loginHandler)
  ....еще handlerы...
  err1 := http.ListenAndServe(port, nil)
  if err1 != nil {	log.Fatal("ListenAndServe: ", err1)	}
}

func loginHandler(w http.ResponseWriter, r *http.Request) {
  if r.Method == "GET" {
    t, _ := template.ParseFiles("templates/login.html", "templates/header.html", "templates/footer.html")
    t.ExecuteTemplate(w, "login", nil)
  }
}

When run locally, everything works fine. When downloading to vps and running on it, it starts, but when the page is opened, it panics, the page does not open:

2018/09/10 17:39:47 http: panic serving 85.172.11.140:51035: runtime error: invalid memory address or nil pointer dereference                 
goroutine 93 [running]:                                                                                                                       
net/http.(*conn).serve.func1(0xc4202723c0)                                                                                                    
        /usr/local/go/src/net/http/server.go:1726 +0xd0                                                                                       
panic(0x78ea60, 0xa08ad0)                                                                                                                     
        /usr/local/go/src/runtime/panic.go:502 +0x229                                                                                         
html/template.(*Template).lookupAndEscapeTemplate(0x0, 0x7fc464, 0x5, 0x0, 0x0, 0x0)                                                          
        /usr/local/go/src/html/template/template.go:144 +0x43                                                                                 
html/template.(*Template).ExecuteTemplate(0x0, 0x849120, 0xc420288380, 0x7fc464, 0x5, 0x0, 0x0, 0x0, 0x0)                                     
        /usr/local/go/src/html/template/template.go:133 +0x43                                                                                 
main.loginHandler(0x84c160, 0xc420288380, 0xc4202ae300)                                                                                       
        /Users/evgeniy/go/src/zdrav_1/logic.go:128 +0x5b5                                                                                     
net/http.HandlerFunc.ServeHTTP(0x8197b0, 0x84c160, 0xc420288380, 0xc4202ae300)                                                                
        /usr/local/go/src/net/http/server.go:1947 +0x44                                                                                       
net/http.(*ServeMux).ServeHTTP(0xa180a0, 0x84c160, 0xc420288380, 0xc4202ae300)                                                                
        /usr/local/go/src/net/http/server.go:2337 +0x130                                                                                      
net/http.serverHandler.ServeHTTP(0xc42005b040, 0x84c160, 0xc420288380, 0xc4202ae300)                                                          
        /usr/local/go/src/net/http/server.go:2694 +0xbc                                                                                       
net/http.(*conn).serve(0xc4202723c0, 0x84c660, 0xc420286440)                                                                                  
        /usr/local/go/src/net/http/server.go:1830 +0x651                                                                                      
created by net/http.(*Server).Serve                                                                                                           
        /usr/local/go/src/net/http/server.go:2795 +0x27b

Maybe met someone?

Answer 1

session, _ := mgo.Dial("mongodb://127.0.0.1")
How so, do not check the error!
Most likely, your session after this line is nil, which is what causes the panic.