connect to mongodb in docker from node app in AWS SAM

Question

I am getting errors connecting to mongodb running in a docker container from my Nodejs app running in AWS SAM (used to say "in my host").

I run mongodb like:

$ docker run --name mongo-myapp --rm -d -p 27018:27017 mongo

and I see the results:

$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                      NAMES
ab8248d17d2d        mongo               "docker-entrypoint.s…"   6 minutes ago       Up 6 minutes        0.0.0.0:27018->27017/tcp   mongo-myapp

~~I can successfully connect and insert data using clients running on my host like MongoDB Compass and Robo 3T Community Edition, specifying port 27018.~~

When I attempt to connect with this code running on my host, (not in a docker container):

const { MongoClient } = require('mongodb');
const mongoConnection = 'mongodb://127.0.0.1:27018';
MongoClient.connect(mongoConnection, (err, db) => {
    if (err) {
        console.error("Failed to connect to mongodb server", err);
        return reject(err);
    }
    console.log("Connected successfully to mongodb server");
    resolve(db);
});

I always see the error:

MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27018

I get the same error using another port with all steps, like 27017.

UPDATE

It turns out my code was not running on the host. It was running in another docker container. I did not realize AWS SAM would put my code into a docker container so I did not mention it in the original question.

Now I run my code with mocha test to make sure it will run on my host, and it connects to the mongo database with no problems.

When I launched a local server using AWS SAM's start-api, I had problems. Perhaps the solution will be to specify a network when starting the mongo container as well as the SAM environment.

@DavidMaze No, just Docker Desktop for Mac, like usual for any docker app. — cyrf, Jun 01 '19 at 18:44
Do you have another version of MongoDB or mongod running on the Mac? (besides the Docker image) — Kevin Prasanna R R, Jun 01 '19 at 19:09
@KevinPrasannaRR No, also I can access it with other clients running on my host. — cyrf, Jun 01 '19 at 19:12
@cyrf Did the [mongodb](https://www.npmjs.com/package/mongodb) npm package help? It seems to be working fine — Kevin Prasanna R R, Jun 01 '19 at 19:38
@KevinPrasannaRR I am using 'mongodb'. I'll update my post to show that. — cyrf, Jun 02 '19 at 13:51
@KevinPrasannaRR that is the error object's message value, I don't have a log. Also, I updated the question with to show AWS SAM was the culprit. — cyrf, Jun 02 '19 at 14:17
Oh good you were able to resolve it. Since natively the code you posted would have not given any problems. — Kevin Prasanna R R, Jun 02 '19 at 14:22

score 2 · Accepted Answer · answered Jun 03 '19 at 01:12

2

Now that the problem is known that the Nodejs code was running within a docker container created by AWS SAM, we can help the Nodejs code connect with Mongodb running in a separate docker container with a port exposed on the host with at least one solution:

Change the connection string to mongodb://host.docker.internal:27018 which helps the code in the container to use a service running on the host.

answered Jun 03 '19 at 01:12

cyrf

5,127
6
25
42

Can you explain a little more about this? What is `host.docker.internal`? – Borduhh Jul 28 '20 at 18:26
1

Found this on the Docker Docs: The host has a changing IP address (or none if you have no network access). From 18.03 onwards our recommendation is to connect to the special DNS name host.docker.internal, which resolves to the internal IP address used by the host. This is for development purpose and will not work in a production environment outside of Docker Desktop for Mac. The gateway is also reachable as gateway.docker.internal. – Borduhh Jul 28 '20 at 18:29

score 1 · Answer 2 · answered Jun 01 '19 at 19:23

Install the necessary dependency for mongodb in node.js https://www.npmjs.com/package/mongodb

const MongoClient = require('mongodb').MongoClient;

const url = "mongodb://localhost:27018/testdb";

MongoClient.connect(url, function(err, db) {
  if (err) throw err;
  console.log("Database created!");
  db.close();
});

score 1 · Answer 3 · answered Jun 01 '19 at 19:43

1

Since you are able to connect from other clients in the same host, I assume that the container is bound to specific external facing ip of the host.

Can you try connecting to the ip of the host instead of 127.0.0.1

Eg: mongodb://external-ip:27018

Though the mapping -p 27018:27017 should bind the port to all ips, you can enforce this by -p 0.0.0.0:27018:27017.

answered Jun 01 '19 at 19:43

Shirine

101
4

Understand, but specifying ip in code might help us conclude if it's a library issue or docker networking issue. – Shirine Jun 02 '19 at 14:07
I tried using 0.0.0.0 in the connection string in my code, but the error is the same. Also please notice I updated the question as I learned AWS SAM was the culprit. – cyrf Jun 02 '19 at 14:27

connect to mongodb in docker from node app in AWS SAM

3 Answers3