MongoTimeoutError：服务器选择在连接到mongoDB时30000毫秒后超时

Question

当我连接到mongodb：// localhost：27017 / myapp时，代码工作正常

但是当我尝试连接到MongoDB MLab数据库帐户时，代码给出 MongoTimeoutError：服务器选择在30000毫秒后超时

更多链接-https://github.com/Automattic/mongoose/issues/8485

server.js

const http = require('http');
const app = require('./app');
const port = process.env.PORT || 3000;
const mongoose = require(`mongoose`);
const key = require('./config');

const server = http.createServer(app);
server.listen(port, () => {
    console.log(`server running on ${port}`);
});
mongoose.set('useUnifiedTopology', true);
mongoose.set('useFindAndModify', false);
const url = process.env.MONGODB_URI || key.MONGO_URL;

const option = {
    useNewUrlParser: true
};

mongoose.Promise = global.Promise;
mongoose.connect(url, option).then(() => console.log('Database connected'))
    .catch((err) => console.log(err));

控制台错误

    at new MongooseTimeoutError (/home/sachin/Desktop/Freelancing/Sahi Price/Data Upload/node_modules/mongoose/lib/error/timeout.js:22:11)
    at NativeConnection.Connection.openUri (/home/sachin/Desktop/Freelancing/Sahi Price/Data Upload/node_modules/mongoose/lib/connection.js:763:19)
    at Mongoose.connect (/home/sachin/Desktop/Freelancing/Sahi Price/Data Upload/node_modules/mongoose/lib/index.js:332:15)
    at Object.<anonymous> (/home/sachin/Desktop/Freelancing/Sahi Price/Data Upload/server.js:20:10)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:831:12)
    at startup (internal/bootstrap/node.js:283:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:622:3)
  message: 'Server selection timed out after 30000 ms',
  name: 'MongooseTimeoutError',
  [Symbol(mongoErrorContextSymbol)]: {} }