Docker Network

Before we proceed to MongoDB, there is an important concept we need to learn — Docker Network.

Currently, when we have containers on our host system, each container has its own ports. These containers cannot interact with each other without going through some port.

But when we set up MongoDB and Mongo Express for our Node.js application, we want both their containers to interact with each other without any port limitations.

For this purpose, we set up something called a Docker Network.

Docker has the ability to create isolated networks — if we put two containers inside the same network, they can interact with each other directly without needing any port, localhost, or anything else.

Docker Network Commands

See All Docker Networks

docker network ls

Create a New Network

docker network create mongo-network

Now we can set up both our containers inside this common network so they can interact with each other without any port.

Why Use Docker Networks?

Setting Up MongoDB and Mongo Express Containers

Setting Up MongoDB Container

docker run -d \
  -p 27017:27017 \
  --name mongo \
  --network mongo-network \
  -e MONGO_INITDB_ROOT_USERNAME=admin \
  -e MONGO_INITDB_ROOT_PASSWORD=qwerty \
  mongo

Since the image is not available locally, Docker will first fetch it.

After downloading all layers, our container is successfully running.

Verify MongoDB Container

docker ps

This verifies that the mongo container is running.

Setting Up Mongo Express Container

docker run -d \
  -p 8081:8081 \
  --name mongo-express \
  --network mongo-network \
  -e ME_CONFIG_MONGODB_ADMINUSERNAME=admin \
  -e ME_CONFIG_MONGODB_ADMINPASSWORD=qwerty \
  -e ME_CONFIG_MONGODB_URL=mongodb://admin:qwerty@mongo:27017/ \
  mongo-express

Important

In the ME_CONFIG_MONGODB_URL, the @mongo part refers to the name of the MongoDB container.

mongodb://admin:qwerty@mongo:27017/

If you named your MongoDB container something different, use that container name instead.

Since both containers are inside the same Docker network, Mongo Express can communicate directly with MongoDB using the container name.

Verify Both Containers

docker ps

Now we have two running containers.

Accessing Mongo Express

Visit:

http://localhost:8081

in your browser.

If a sign-in option appears, Mongo Express is working successfully.

Default Credentials

After signing in, you will see the default MongoDB database setup.

Here we can see that:

• mongo container → runs the actual MongoDB database.
• mongo-express container → provides the graphical user interface to view and manage that database.

Creating Our Database

Create a new database called:

college-db

Inside it, create a collection called:

users

We can also add a new document:

{
  "email": "john@yahoo.in",
  "username": "JohnDoe",
  "password": "secret"
}

Testing the Connection

Now let's test whether our MongoDB database is connected to our Node.js application.

Send a GET request to:

localhost:5050/get-users

The output shows our document.

This means the same document we added through Mongo Express is now visible through our Node.js application.

We did not install MongoDB on our local system, yet our Node.js application was able to connect to the MongoDB database running inside the Docker container.

End-to-End Flow

User
  |
  v
Node.js App (Port 5050)
  |
  v
MongoDB Container (mongo)
  ^
  |
Mongo Express (Port 8081)

1. User sends a request to the Node.js application.
2. Node.js communicates with the MongoDB container.
3. Data is stored or retrieved from the college-db database.
4. Mongo Express allows us to view and manage the same data through the browser.

Testing with POST Request

We can also test with a POST request from the application's home page.

Steps

1. Open the application UI.
2. Create a new account.
3. Check Mongo Express for the newly added document.
4. Send a GET request to:

localhost:5050/get-users

1. Verify that the new user data is returned.

This confirms that:

• The Node.js application is connected successfully.
• MongoDB is running inside a Docker container.
• Mongo Express can manage the database visually.
• All components are communicating correctly through the Docker network.