部署MERN应用至Heroku时出现应用错误，请求技术帮助

我正在完成训练营最后一项作业，时间紧迫。将MERN应用部署到Heroku时出现应用错误，尝试过以下操作但未解决：

• 删除并重装node_modules
• 在package.json中添加node和npm版本
• 执行npm update
• 重启Heroku
• 修改PORT配置
• 多次重写连接文件和服务文件

怀疑问题出在MongoDB或Apollo配置遗漏，或者.env密钥配置错误。

当前配置文件 #

package.json #

{"name": "server", "version": "1.0.0", "description": "", "main": "server.js", "scripts": {"start": "node server.js", "watch": "nodemon server.js"}, "keywords": [], "author": "Wren Sanchez", "license": "ISC", "dependencies": {"bcrypt": "^5.0.0", "express": "^4.17.1", "dotenv": "^16.0.1", "graphql": "^15.5.0", "jsonwebtoken": "^8.5.1", "mongoose": "^5.9.10", "apollo-server-express": "^3.6.1", "nodemon": "^2.0.3"}, "devDependencies": {"nodemon": "^2.0.3"}}

server.js #

const { ApolloServer } = require("apollo-server-express");
const express = require('express');
const path = require('path');
const db = require('./config/connection');
const { typeDefs, resolvers } = require("./schemas");
const { authMiddleware } = require('./utils/auth');
require('dotenv').config();

const app = express();
const PORT = process.env.PORT || 3001;

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: authMiddleware,
  cache: "bounded",
});

app.use(express.urlencoded({ extended: false }));
app.use(express.json());

if (process.env.NODE_ENV === 'production') {
  app.use(express.static(path.join(__dirname, '../client/build')));
}

app.get('/', (req, res) => {
  res.sendFile(path.join(__dirname, '../client/build/index.html'));
});

const startApolloServer = async (typeDefs, resolvers) => {
  await server.start();
  server.applyMiddleware({ app });

  db.once("open", () => {
    app.listen(PORT, () => {
      console.log(`API server running on port ${PORT}!`);
      console.log(
        `Use GraphQL at http://localhost:${PORT}${server.graphqlPath}`
      );
    });
  });

startApolloServer(typeDefs, resolvers);
}

connection.js #

const mongoose = require('mongoose');
require('dotenv').config({ path: '../.env' });

mongoose.connect(process.env.MONGODB_URI || 'mongodb://localhost:27017/googlebooks', {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

module.exports = mongoose.connection;

排查建议 #

1. 检查Heroku环境变量配置：

   • 确认Heroku的Config Vars中已正确设置MONGODB_URI，值为远程MongoDB（如MongoDB Atlas）的连接字符串，本地.env文件不会被推送到Heroku，必须在Heroku后台配置。
   • 若使用了其他.env密钥（如JWT_SECRET），也需同步到Heroku Config Vars。

2. 修复server.js语法错误：

   • startApolloServer函数存在括号闭合缺失，导致语法错误，修正后代码如下：

     const startApolloServer = async (typeDefs, resolvers) => {
       await server.start();
       server.applyMiddleware({ app });
     
       db.once("open", () => {
         app.listen(PORT, () => {
           console.log(`API server running on port ${PORT}!`);
           console.log(
             `Use GraphQL at http://localhost:${PORT}${server.graphqlPath}`
           );
         });
       });
     }; // 补充缺失的函数闭合括号
     
     startApolloServer(typeDefs, resolvers);
     

3. 调整connection.js的dotenv加载方式：

   • Heroku部署时，../.env路径可能无效，建议去掉路径参数，直接用require('dotenv').config();，依赖Heroku Config Vars提供环境变量即可。

4. 配置Heroku自动构建客户端：

   • 在package.json的scripts中添加postinstall脚本，确保Heroku部署时自动构建客户端：

     "scripts": {
       "start": "node server.js",
       "watch": "nodemon server.js",
       "heroku-postbuild": "cd client && npm install && npm run build"
     }
     

5. 查看Heroku实时日志：

   • 执行heroku logs --tail查看错误详情，日志会明确显示问题根源（如数据库连接失败、语法错误、依赖缺失等）。

6. 指定Node/npm版本：

   • 在package.json中添加engines字段，确保Heroku使用和本地一致的版本：

     "engines": {
       "node": "16.x",
       "npm": "8.x"
     }
     

内容的提问来源于stack exchange，提问作者Wren Sanchez