Docker Networking Introduction

Containers are isolated, but real applications still need to communicate.

A web container may need to talk to a database container. Your browser may need to reach a containerized application. A container may need internet access to download packages or call an API.

Docker networking is the system that makes those connections possible.

What networking solves

Docker networking answers three common questions:

• How does my browser reach a container?
• How does one container talk to another container?
• How does a container reach the internet?

The answer depends on the network type and port mapping.

Container isolation

Each container gets its own network view. It can have its own IP address, routes, and network interfaces.

This isolation is useful because containers do not all fight over the same internal ports.

For example, two containers can both listen on port 80 internally, as long as the host exposes them on different ports:

docker run -d -p 8081:80 nginx
docker run -d -p 8082:80 nginx

Port mapping

Port mapping connects a host port to a container port:

docker run -p 8080:80 nginx

This means:

host port 8080 -> container port 80

Without port mapping, your container may be running perfectly but still not reachable from your browser.

Container-to-container communication

Containers can communicate through Docker networks.

Custom bridge networks are especially useful because containers can find each other by name.

docker network create app-network
docker run -d --name database --network app-network mysql
docker run -d --name api --network app-network my-api

Inside app-network, the API can reach the database using the container name database.

What to focus on first

Learn these ideas in order:

Written By: Shiva Srivastava