I can connect to a google cloud deployed mongoDB from localhost but not from the same app when deploying on the app engine

问题

My app is written in React and Express using Mongoose for the db. I deployed a bitnami mongoDB instance on google compute engine. Now I'm trying to deploy the server on the App engine. When I run my app locally it connects fine to the db (I can add stuff and see it). But when I do an npm start in the google cloud shell is get this error:

'failed to connect to server [35.196.182.249:27017] on first connect [MongoError: connection 0 to 35.196.182.249:27017 timed out]' }
(node:1310) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): MongoError: failed to connect to server [35.196.182.249:27017] on first connect [MongoError: connection 0 to 35.196.182.249:27017 timed out]

Here is my code to connect:

mongoose.connect(process.env.MONGODB_URI,{
    useMongoClient: true
}).catch(function(err){
    console.log(err)
});

where MONGODB_URI=mongodb://root:password@XX.XXX.XXX.XXX:27017, password is the password I got from the compute engine, and XX.XXX.XXX.XXX is the external IP provided by the compute engine. I use the same URI when connecting locally and in the google cloud shell but it only connects from localhost. I tried hardcoding in the URI too and it didn't work. Any ideas?

来源：https://stackoverflow.com/questions/45601970/i-can-connect-to-a-google-cloud-deployed-mongodb-from-localhost-but-not-from-the