🛳️ Docker Series: Episode 7 — Docker Networking: How Containers Talk Behind the Scenes

This content originally appeared on DEV Community and was authored by Yash Sonawane

“Ever wondered how your frontend talks to your backend inside Docker? Or how multiple containers magically connect like best friends at a tech meetup? In this episode, we dive into Docker networking — simply and visually.”

Why Docker Networking Matters

In real-world apps, you don’t just run a single container.
You often run:

• A frontend (React, Vue, etc.)
• A backend (Node, Django, etc.)
• A database (MongoDB, Postgres, etc.)

These containers need to talk to each other, securely and efficiently.
Docker’s networking system makes this possible.

Types of Docker Networks

For most use cases (especially Docker Compose), Bridge is what you need.

Default Bridge Network

When you run containers without specifying a network:

docker run -d --name nginx nginx

Docker connects them to the bridge network. But by default, containers can’t talk to each other by name here.

You’d have to use IPs — not ideal. So let’s fix that.

Create a Custom Bridge Network

docker network create my-network

Now, run containers and attach them:

docker run -d --name backend --network my-network my-backend-image

docker run -d --name frontend --network my-network my-frontend-image

Now frontend can reach backend using its container name as hostname.
Example: http://backend:5000

Real Example: Node App + MongoDB

# Create custom network
docker network create dev-net

# Run MongoDB
docker run -d \
  --name mongo \
  --network dev-net \
  mongo

# Run Node app connected to mongo
docker run -d \
  --name app \
  --network dev-net \
  my-node-app

Inside my-node-app, you can now connect to Mongo using:

mongodb://mongo:27017

Inspecting Networks

List networks:

docker network ls

Inspect a network:

docker network inspect my-network

Port Mapping (Host Container)

Want to access your app in the browser?

docker run -d -p 8080:3000 my-app

This maps:

• Port 3000 inside the container
• To port 8080 on your machine

Visit: http://localhost:8080

Key Takeaways

• Use custom bridge networks to let containers talk by name
• Use --network when running multi-container apps
• Inspect networks to understand connections

Up Next: Docker Compose — One YAML to Rule Them All

In Episode 8, we’ll cover:

• How to run multi-container apps with one command
• Docker Compose file structure
• Real-world project with frontend + backend + DB

Over to You

Have you tried connecting containers via network yet?
Was the custom bridge easier than expected?

Comment below with your Docker networking wins or pain points!

If this episode made container networking click for you, share it with your dev buddy or team.

Next: “Docker Compose — Build Multi-Container Apps Like a Boss”

This content originally appeared on DEV Community and was authored by Yash Sonawane