The server doesn’t respond anymore after I switch framework Gin to Echo

I used to use Gin(Golang framework) and deploy docker image to GKE.
It was working totally fine.

But the server doesn’t respond anymore when I switched Gin to Echo(it is also Golang framework)

I think it is because there is something wrong with port combination(port forwarding).

My echo server code is like below.

func main() {
    e := presentation.Router()

    e.Logger.Fatal(e.Start(":8080")) // listen and serve on :8080
}

and my dockerfile is like below.

FROM alpine:3.9

WORKDIR /app
ADD main /app

ENV PORT 80

EXPOSE 80

CMD ["./main"]

When request reaches to 80 port, it has to render to 8080 port (container port).
But it doesn’t seem that it is working like above at the moment.

How can I match outer port and inner port??

Source: StackOverflow