mongoose不会连接到ec2 mongodb实例

我正在尝试创建一个节点。连接到托管在ec2实例上的mongodb的js服务器。我是这样做的:

mongoose.connect("mongodb://username:password@ec2-xx-xx-xxx-xxx.eu-central-1.compute.amazonaws.com:27017/dbname");

db.on('error', err => {
    console.log('Mongoose default connection error:', err);
    db.close();
});

db.once('open', () => {
    console.log(`Mongoose default connection open`);
});

但它一直在告诉我这个错误:

Mongoose default connection error: { MongoError: failed to connect to server [xxx] on first
 connect [MongoError: connect ETIMEDOUT xxx:27017]
    at Pool.<anonymous> (/Users/jmisiti/hm-landing/node_modules/mongodb-core/lib/topologies/server.js:336:35)
    at emitOne (events.js:115:13)
    at Pool.emit (events.js:210:7)
    at Connection.<anonymous> (/Users/jmisiti/hm-landing/node_modules/mongodb-core/lib/connection/pool.js:280:12)
    at Object.onceWrapper (events.js:318:30)
    at emitTwo (events.js:125:13)
    at Connection.emit (events.js:213:7)
    at Socket.<anonymous> (/Users/jmisiti/hm-landing/node_modules/mongodb-core/lib/connection/connection.js:189:49)
    at Object.onceWrapper (events.js:316:30)
    at emitOne (events.js:115:13)
    at Socket.emit (events.js:210:7)
    at emitErrorNT (internal/streams/destroy.js:62:8)
    at _combinedTickCallback (internal/process/next_tick.js:102:11)

    at process._tickCallback (internal/process/next_tick.js:161:9)
  name: 'MongoError',
  message: 'failed to connect to server [xxx] on first connect [MongoError: connect ETIMEDO
UT xxx:27017]' }

我的连接字符串是百分之百确定的工作。我的mongoose版本与我的mongodb版本配合得很好。有什么想法吗?:)

PS:27017上的端口已打开,并且已经有一个aws实例在使用我的mongodb。所以我相信这是可行的。