问题
I'm using Bitnami mongodb instance deployed on Google Compute Engine.
I can connect to that mongodb instance through MongoDB clients from my personal computer using the External IP of MongoDB instance.
My app is an Angular2 app with Node.js backend. Following is the connection string format used in server.js
mongoose.connect('mongodb://<username>:<password>@<External IP>:27017/<dbname>');
When I host my app on localhost it can connect to mongodb instance on the cloud and access data without issues.
But, when the app is deployed on google app engine the app no longer connects to the mongodb. Following is the error.
MongoError: failed to connect to server [<External IP>:27017] on first connect
Can somebody suggest what is the root cause.
回答1:
App Engine instances are part of the same private internal network as Compute Engine instances. Your App Engine application can communicate with services hosted on Compute Engine within the same project without going through the public internet. In many cases, your application connects to the service using the instance's internal IP address without needing to assign the database an external, public IP address. If desired, you can assign a public IP address to allow the database to be accessed from outside of Google Cloud Platform.
Also, App Engine applications can connect to databases via public Ip if the database server and firewall are configured properly to accept connections. Your App Engine application connects to the database using the service's public IP address.
By default, mongodb daemon is listening on TCP port 27017. Therefore, you will need to add a firewall rule on Compute Engine firewall for this port and protocol. This can be done using Google Cloud console or using gcloud command tool:
gcloud compute firewall-rules create allow-mongodb --allow tcp:27017
来源：https://stackoverflow.com/questions/42187507/cannot-connect-to-mongodb-after-app-deploys-on-google-app-engine