Container Communication: Configuring Docker Networks

Docker containers are isolated by default. To allow containers to communicate with each other securely, Docker uses Networks.

1. Network Drivers Reference

• Bridge (Default): Creates a private internal network on your host machine. Containers on the same bridge network can communicate, while remaining isolated from external networks.
• Host: Removes isolation between the container and the host machine. The container shares the host's network namespace directly.
• None: Disables all networking for the container.

2. Setting Up Container Communication

To connect a web application container to a database container:

Step 1: Create a Custom Bridge Network

Do not use the default bridge network, as it does not support automatic container name resolution (DNS):

# Create network named 'app-net'
docker network create app-net

Step 2: Run the Database Container

Run your database container on the custom network:

docker run -d --name database-server --network app-net postgres

Step 3: Run the Web Application Container

Run your application container on the same network:

docker run -d --name api-server --network app-net -p 3000:3000 my-api-image

Because both containers are on app-net, the application container can connect to the database container using its name as the hostname: database-server (for example, postgres://database-server:5432).

3. Managing Networks via CLI

Use these commands to manage networks:

# List all active networks
docker network ls

# Inspect network configurations and connected containers
docker network inspect app-net

# Disconnect a container from a network
docker network disconnect app-net api-server