google app engine – deploying simple golang app to appengine has stopped working-ThrowExceptions

Exception or error:

I have created a small test app in golang and am trying to deploy it to Google AppEngine and although the “gcloud app deploy” command seems to work and reports no errors, when I visit the endpoint -> it just sits there and eventually gives me a 500 response, and displays the error (in the browser)

Error: Server Error
The server encountered an error and could not complete your request.
Please try again in 30 seconds.

I am fairly new go golang and AppEngine but I have made several working apps recently and I am completely stumped as to why it’s not working.

When I type “gcloud app logs tail -s default” I see some log entries like:

2019-09-06 02:17:31 default[20190905t204717]  "GET / HTTP/1.1" 500
2019-09-06 02:17:32 default[20190905t204717]  Starting the application...
2019-09-06 02:22:08 default[20190905t212008]  "GET / HTTP/1.1" 500
2019-09-06 02:22:08 default[20190905t212008]  Starting the application...
2019-09-06 02:22:14 default[20190905t212008]  "GET /cards HTTP/1.1" 500
2019-09-06 02:22:17 default[20190905t212008]  "GET /cards HTTP/1.1" 500
2019-09-06 02:22:17 default[20190905t212008]  Starting the application...

Here is the simple single file go app “main.go “

package main
import (
func main() {
    fmt.Println("Starting the application...")
    router := mux.NewRouter()
    router.HandleFunc("/cards", GetCardsEndpoint).Methods("GET")
    err := http.ListenAndServe(":80", router)
    fmt.Println("ERR:", err)
func GetCardsEndpoint(response http.ResponseWriter, request *http.Request) {
    fmt.Println("API: GetCardsEndpoint() ")
    err := json.NewEncoder(response).Encode("cards api here")
    fmt.Println("API: GetCardsEndpoint() err:", err )

The app.yaml

runtime: go111

It should return text: “cards api here”

How to solve:

I figured it out, basically, there were 2 things wrong here:

1) I needed to type “dep init” and “dep ensure -update” in the root of my project.
(that downloads all the dependencies into your project folder so that they can be uploaded with your app.)

2) I don’t think we are supposed to specify a port in our code we are supposed to make the listen port taken from os.GetEnv(“PORT) on an AppEngine server

instead of:

err := http.ListenAndServe(":80", router)

It sould be

err := http.ListenAndServe(":"+os.getEnv("PORT"), router)

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