Docker Networking

By default, containers are isolated from each other and from the host network. Docker's networking model lets you control precisely how containers communicate — with each other, with the host, and with the outside world.

Docker Network Drivers

Docker supports several network drivers:

• bridge — the default for standalone containers; creates an isolated private network on the host
• host — removes network isolation; the container shares the host's network stack directly
• none — disables all networking; useful for batch jobs that need no network access
• overlay — connects containers across multiple Docker hosts (used with Docker Swarm)

The Default Bridge Network

When you run a container without specifying a network, it attaches to the default bridge network. Containers on the default bridge can reach each other by IP address but not by name.

# Inspect the default bridge network
docker network inspect bridge

# See a container's IP address
docker inspect --format '{{.NetworkSettings.IPAddress}}' my-container

User-Defined Bridge Networks

User-defined bridge networks are superior to the default bridge because they provide automatic DNS resolution — containers can reach each other by container name, not just by IP.

# Create a user-defined bridge network
docker network create my-network

# Run two containers on the same network
docker run -d --name backend --network my-network my-backend-image
docker run -d --name frontend --network my-network my-frontend-image

# The frontend container can reach the backend by name:
# http://backend:8080
# No need to look up IP addresses

# List networks
docker network ls

# Remove a network
docker network rm my-network

Port Publishing

Containers have their own internal network; to reach a service from outside you must publish a port. This maps a port on the host to a port inside the container.

# Publish port 80 inside the container to port 8080 on the host
docker run -d -p 8080:80 nginx

# Bind to a specific host interface (localhost only)
docker run -d -p 127.0.0.1:8080:80 nginx

# Publish to a random available host port
docker run -d -p 80 nginx

# See which host port was assigned
docker port <container-name> 80

Connecting Containers in Practice

A typical web application has a frontend service, a backend API, and a database. Each runs in its own container. With a user-defined network, they can communicate by name:

docker network create app-network