为什么应用程序在 localhost 上运行但在部署时导致 CANNOT GET /？

Question

So I built myself a personal portfolio website using the MERN stack, and everything was working well on localhost, so I decided to deploy it using Google App Engine. I delpoyed the frontend and backend as two seperate services as recommended by this tutorial. The frontend works great (see https://personal-website-279319.wl.r.appspot.com/ ), but the backend doesn't. If you look under the "project" tab, nothing shows up as the backend is unable to connect to Mongo Atlas and actually retrieve the data.

The code for server.js, the start page for the backend is as follows:

require('@google-cloud/debug-agent').start();
const express = require('express');
const cors = require('cors');
const mongoose = require('mongoose');
require('dotenv').config();

// Initialize Dependnecies and Set Port?
const app = express();
const port = process.env.PORT || 5000;

app.use(cors());
app.use(express.json());

// Connect To Mongoose
const uri = process.env.ATLAS_URI;
mongoose.connect(uri, { useNewUrlParser: true, useCreateIndex: true, useUnifiedTopology: true });

const connection = mongoose.connection;
connection.once('open', () => {
  console.log("MongoDB database connection established successfully");
})

// Connect URL Ending to Router
const contactRouter = require('./routes/contact');
const projectRouter = require('./routes/project');

app.use('/contact', contactRouter);
app.use('/projects', projectRouter);

// Listen for Connection on Port 
app.listen(port, () => {
    console.log(`Server is running on port: ${port}`);
});

The rest of the code can be found on the Github repository here if you'd like to see. I did make sure this script would run on start by putting this snippet of code in package.json.

  "scripts": {
    "start": "node server.js",
    "test": "echo \"Error: no test specified\" && exit 1"

When I go to the service api ( https://api-dot-personal-website-279319.wl.r.appspot.com/ ) directly, I get a page saying Cannot Get /. I checked the console and the message that's supposed to say the "connection to MongoDB established successfully" isn't there. I did get a message saying "Content Security Policy" was blocking the loading of some favicon (I'm not sure why.) I tried to fix this by changing the /routes/projects code to try to prevent this

/* Route Get (Everything) Request */
router.route('/').get((req, res) => {
    res.setHeader("Content-Security-Policy", "");
    Project.find()
    .then(projects => res.json(projects))
    .catch(err => res.status(400).json('Error: ' + err));
});

but that resulted in a 500 Service Error once I deployed it. Honestly, I'm really confused; I think I'm missing something, but I'm not sure what. If someone could explain what I'm doing wrong or lead me in the right direction, that would be much appreciated, thanks.

Answer 1

You're Atlas URI is determined from process.env.ATLAS_URI . If you're using App Engine (standard) you'll want to ensure that the app.yaml file includes a value for this ATLAS_URI environment variable. I suspect you'll need more than just the database URI and may need username|password environment variables too.