Networks & Ports

#Networks & Ports

After this lesson you'll know:

• how containers communicate with each other
• what port mapping means
• how to create custom networks

#Container Communication

Containers are isolated by default. To talk to each other, they need networks.

# Default networks
docker network ls
# bridge, host, none

#Port Mapping

# Host:Port → Container:Port
docker run -p 8080:80 nginx
# Visit http://localhost:8080

# Multiple ports
docker run -p 8080:80 -p 443:443 nginx

#Custom Networks

The cleanest approach: create your own network where containers find each other by name.

# Create a network
docker network create my-net

# Start containers in the network
docker run -d --name web --network my-net nginx
docker run -it --network my-net alpine sh

# Now you can reach the web container simply as "web"
/ # ping web

#Important Commands

docker network ls                      # All networks
docker network inspect bridge           # Network details
docker network connect my-net web       # Connect a container later
docker network disconnect my-net web    # Disconnect

#✋ Try it out

• Create a network testnet, start an Alpine container in it, install curl, start Nginx in the same network as web and curl http://web from the Alpine container
• docker run -d --name api -p 4000:80 nginx — which port on the host? (4000), which port in the container? (80)

#📌 Summary

• Containers in the same network find each other by name
• Port mapping: -p HOST_PORT:CONTAINER_PORT
• docker network create for custom networks