Docker Networking

Docker networking allows containers to communicate with each other, external services, and the host machine.

When building real-world applications, containers rarely operate alone. A typical setup might include:

• A frontend application
• A backend API
• A database server

These services need a reliable way to communicate, and Docker networks provide that functionality.

Understanding Docker Networks

A Docker network is a virtual network that containers can join.

Containers connected to the same network can communicate using container names rather than IP addresses.

For example:

frontend
    │
    ▼
backend
    │
    ▼
database

The backend can connect to the database using:

database:5432

instead of:

localhost:5432

This works because Docker provides automatic DNS resolution for containers on the same network.

Viewing Existing Networks

To list all available Docker networks:

docker network ls

Example output:

NETWORK ID     NAME      DRIVER
abc123         bridge    bridge
def456         host      host
ghi789         none      null

Default Network Types

Docker ships with several built-in network drivers.

Bridge Network

The default network used by most containers.

Container A
      │
      ▼
Bridge Network
      ▲
      │
Container B

Containers on the same bridge network can communicate with each other.

Host Network

Containers share the host machine's network stack.

docker run --network host nginx

This removes network isolation and is generally used only in specific scenarios.

None Network

Disables networking entirely.

docker run --network none nginx

The container cannot communicate with external systems or other containers.

Creating a Custom Network

Custom networks are recommended for multi-container applications.

Create a network:

docker network create app-network

Verify it was created:

docker network ls

Running Containers on a Network

Start a PostgreSQL container:

docker run -d \
  --name database \
  --network app-network \
  postgres

Start an API container on the same network:

docker run -d \
  --name backend \
  --network app-network \
  my-api

Both containers can now communicate directly.

The backend can reach PostgreSQL using:

database:5432

Inspecting a Network

To view detailed information about a network:

docker network inspect app-network

This command displays:

• Connected containers
• Network settings
• Subnets
• Gateway information

Connecting Existing Containers

You can attach an existing container to a network.

docker network connect app-network backend

To disconnect it:

docker network disconnect app-network backend

Removing a Network

Delete an unused network:

docker network rm app-network

Docker will prevent removal if active containers are still connected.

Best Practices

Use Custom Networks

Avoid placing all containers on the default bridge network.

Custom networks provide:

• Better isolation
• Cleaner service discovery
• Easier troubleshooting

Use Container Names

Prefer:

database:5432

Instead of:

172.17.0.2:5432

Container names remain stable while IP addresses can change.

Separate Applications

Create dedicated networks for each application stack.

Example:

frontend-network
backend-network
monitoring-network

This improves security and organization.

Summary

Docker networks enable containers to communicate securely and efficiently.

Key takeaways:

• Containers communicate through networks.
• Docker provides built-in DNS resolution.
• Custom networks are recommended for production workloads.
• Container names should be used instead of IP addresses.
• Multi-container applications depend heavily on Docker networking.