Docker Networking - Docker & DevOps Tutorial | TechLead

Docker Network Types

Docker provides several network drivers to control how containers communicate with each other and with the outside world.

Network Drivers

bridge: Default network — containers on the same bridge can communicate
host: Container uses the host's network directly (no isolation)
none: No networking — fully isolated container
overlay: Multi-host networking for Docker Swarm

Managing Networks

# List all networks
docker network ls

# Create a custom network
docker network create my-network

# Create with specific subnet
docker network create --subnet=172.20.0.0/16 my-network

# Inspect a network
docker network inspect my-network

# Remove a network
docker network rm my-network

# Remove all unused networks
docker network prune

Connecting Containers

Containers on the same user-defined bridge network can reach each other by container name — Docker provides built-in DNS resolution.

# Create a network for our app
docker network create app-network

# Run a database on the network
docker run -d \
  --name db \
  --network app-network \
  -e POSTGRES_PASSWORD=secret \
  postgres:16

# Run the app on the same network
docker run -d \
  --name api \
  --network app-network \
  -e DATABASE_URL=postgres://postgres:secret@db:5432/postgres \
  -p 3000:3000 \
  myapi:latest

# The api container can reach db by name "db"!

Port Mapping

# Map host port to container port
docker run -d -p 8080:80 nginx        # host:container

# Map multiple ports
docker run -d -p 80:80 -p 443:443 nginx

# Map to specific host interface
docker run -d -p 127.0.0.1:8080:80 nginx

# Map a range of ports
docker run -d -p 8000-8010:8000-8010 myapp

# Let Docker choose a random host port
docker run -d -p 80 nginx
docker port   # See assigned port

Practical Example: Full Stack App

# Create a shared network
docker network create fullstack

# Database
docker run -d \
  --name postgres \
  --network fullstack \
  -v pgdata:/var/lib/postgresql/data \
  -e POSTGRES_PASSWORD=secret \
  -e POSTGRES_DB=myapp \
  postgres:16

# Redis (for caching/sessions)
docker run -d \
  --name redis \
  --network fullstack \
  redis:7-alpine

# Backend API
docker run -d \
  --name api \
  --network fullstack \
  -e DATABASE_URL=postgres://postgres:secret@postgres:5432/myapp \
  -e REDIS_URL=redis://redis:6379 \
  -p 4000:4000 \
  myapi:latest

# Frontend
docker run -d \
  --name frontend \
  --network fullstack \
  -e API_URL=http://api:4000 \
  -p 3000:3000 \
  myfrontend:latest

Connect/Disconnect from Networks

# Connect a running container to a network
docker network connect app-network my-container

# Disconnect from a network
docker network disconnect app-network my-container

# A container can be on multiple networks
docker network connect frontend-network api
docker network connect backend-network api

Key Takeaways

✅ Always create custom networks — don't rely on the default bridge
✅ Containers on the same network communicate by name (DNS)
✅ Only expose ports to the host when external access is needed
✅ Use 127.0.0.1 binding for ports you want to keep local