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.

Answer 1

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:

1. 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.