如何通过FireBase云功能部署服务器

basic example 设置一个Express服务器来访问托管在Google云平台上的Mongo实例。但当我执行命令时

firebase deploy --only functions

mongoServer

functions/index.ts

import * as admin from 'firebase-admin';
import * as functions from 'firebase-functions';
import { mongoApp } from './mongo/mongo-server';
import { onSendNotification } from './notifications/send-notification';
import { onImageSave } from './resize-image/onImageSave';
admin.initializeApp();

export const onFileChange = functions.storage.object().onFinalize(onImageSave);
export const sendNotification = functions.https.onRequest(onSendNotification);
export const mongoServer = functions.https.onRequest(mongoApp); // this one fails

mongo-server.ts

import * as bodyParser from 'body-parser';
import * as express from 'express';
import * as mongoose from 'mongoose';
import { apiFoods } from './foods.api';
import { Mongo_URI, SECRET_KEY } from './mongo-config';

const path = require('path');

export const mongoApp = express();

mongoApp.set('port', (process.env.PORT || 8090));
mongoApp.use(bodyParser.json());
mongoApp.use(bodyParser.urlencoded({ extended: false }));

connect()
  .then((connection: mongoose.Connection) => {
    connection.db
      .on('disconnected', connect)
      .once('open', () => {

        console.log('Connected to MongoDB');
        apiFoods(mongoApp);

        mongoApp.listen(mongoApp.get('port'), () => {
          console.log('Listening on port ' + mongoApp.get('port'));
        });

      });
  }).catch(console.log)

function connect(): Promise<mongoose.Connection> {
  return mongoose
    .connect(Mongo_URI)
    .then((goose) => { return goose.connection })
    .catch(err => {
      console.log(err)
      return null;
    });
}