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Docker networking allows containers to communicate with each other and the outside world. When you install Docker, it automatically creates three default networks.
You can view the default networks using docker network ls:
The default bridge network is considered legacy and has drawbacks (like no automatic DNS resolution between containers). For production, you should always create user-defined bridge networks.
# Create a new network
docker network create my-custom-network
Now, you can attach multiple containers to this network. Crucially, containers on a user-defined network can resolve each other by their container name!
# Start a database container on the network
docker run -d --name my-db --network my-custom-network postgres
# Start a web app container on the same network
docker run -d --name my-web --network my-custom-network my-web-image
Inside the my-web container, you can now connect to the database using the hostname my-db instead of an IP address.
By default, containers cannot be accessed from the host machine or the outside world. You must explicitly publish ports using the -p flag.
docker run -p 8080:80 nginx
This maps port 8080 on your host machine to port 80 inside the container.
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