Connecting to MongoDB in Docker from external app - node.js

Question

Is it possible to connect to a docker container running a MongoDB image from an external nodejs application running locally? I've tried connecting via localhost:27017. Here's the docker compose file I'm using:
version: '3'
services:
mongodb:
image: 'bitnami/mongodb:3.6.8'
ports:
- "27017:27017"
environment:
- MONGODB_ROOT_PASSWORD=$MONGODB_ROOT_PASSWORD
- MONGODB_USERNAME=$MONGODB_USERNAME
- MONGODB_PASSWORD=$MONGODB_PASSWORD
- MONGODB_DATABASE=$MONGODB_DATABASE
volumes:
- /data/db:/bitnami
I try connecting to it with the following url with no luck:
mongodb://${process.env.MONGODB_USERNAME}:${process.env.MONGODB_PASSWORD}#localhost:27017
EDIT: Connecting via mongodb://localhost:27017 works, but the authentication url errors out. I printed out the result of this string and there's nothing particularly wrong with it. I verified that the username and password match the users inside mongo in the docker container.
app.listen(port, () => {
console.log(`Example app listening on port ${port}!`);
const url = (() => {
if(process.env.MONGODB_USERNAME && process.env.MONGODB_PASSWORD) {
return `mongodb://${process.env.MONGODB_USERNAME}:${process.env.MONGODB_PASSWORD}#localhost:27017/`;
}
console.log('could not find environment vars for mongodb');
})();
MongoClient.connect(url, (err, client) => {
if(err) {
console.log('DB connection error');
} else {
console.log("Connected successfully to server");
client.close();
}
});
});

Answer 1

If the external nodejs application is also running in a docker container then you need to link the containers. Here is an example of a docker run cmd that links containers. I added environment variables to illustrate what host name and port you would use from inside the container.
docker run -d -it -e DEST_PORT=27017 -e DEST_HOST='mongodb' --link mongodb external-application:latest

Answer 2

It's important to always check the result of docker logs <container-name> --tail 25 -f. From my point of view, I think it is an issue related to permissions on this directory '/bitnami/mongodb'. Check out sameersbn comment how to fix this permission issue.
I'll assume it's the compose specification then. Try the following configuration
environment:
MONGODB_ROOT_PASSWORD:$MONGODB_ROOT_PASSWORD
MONGODB_USERNAME:$MONGODB_USERNAME
MONGODB_PASSWORD:$MONGODB_PASSWORD
MONGODB_DATABASE:$MONGODB_DATABASE
volumes:
- '/data/db:/data/db'

Answer 3

The issue turned out to be that I had changed the password in MONGODB_PASSWORD (it had an # in it so I thought it would have interfered with the string parsing, so I consequently changed it). The problem is, when the container restarts it references the same volume (as it should), so the users were never updated and as a result I was logging in with the wrong credentials.