Docker Networks: Connecting Containers with Ease

I was trying to get a web app and a database to talk last week.

The web app kept timing out, and I was clueless. Turns out, I’d forgotten to put both containers on the same network.

Docker networks make it easy for containers to find each other without messing up with IP addresses.

Your 5-Minute Win

The Problem
Containers on different networks can’t see each other. Even if they’re on the same host, they need to be on the same network to communicate.

The Solution
Put both on the same user-defined network and use service names as hostnames.

Step 1: Create a network:

docker network create my-app-net

This creates a private network for your containers.

Step 2: Run your database:

docker run -d --name db --network my-app-net mysql

The --network flag connects the container to the new network.

Step 3: Run your web app:

docker run -d --name webapp --network my-app-net busybox ping mysql

Now the web app (busybox) pings the database (mysql) by name.

You can use docker compose to have similar result.

services:
  webapp:
    image: busybox
    command: ["ping", "redis"]
    networks:
      - app-network

  redis:
    image: "redis:alpine"
    networks:
      - app-network

networks:
  app-network:
    driver: bridge

The Breakdown:

docker-compose.yml defines two services (webapp and redis).
Both are connected to the app-network (a custom bridge network).
The webapp pings redis by its service name, not its IP.

Why It Works:

Docker’s built-in DNS lets containers resolve each other’s names. No IPs, no config.

The Result:

Your app now talks to the database smoothly. No more IP changes or port fights.

The DevOps Radar

Docker Networking Overview

https://docs.docker.com/engine/network/

The official docs explain how networks isolate and connect containers. Perfect for troubleshooting.

Docker Network Overlay vs Bridge - Ultimate Difference

https://devtodevops.com/blog/docker-network-overlay-vs-bridge/

Diagrams and simple examples make complex concepts feel approachable.

Tool of the Week

Command: docker network inspect <network_name>
This is your network’s X-ray. It shows IP ranges, connected containers, and even the driver used. Use it to debug why containers aren’t talking.

Over to You

When would you choose to use the host network driver instead of the default bridge network, and what trade-offs would you be making?