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Docker provides default networks, but for complex applications, custom networks are key. They offer better isolation and controlled communication between your services.

Think of them as private virtual LANs just for your containers, giving you more control over how they interact.

When you run a container without specifying a network, it usually attaches to the bridge network by default. This allows containers to talk to each other and the host.

• Bridge: Default, isolated.
• Host: Container shares host's network stack.
• None: Isolated, no network access.

While useful, the default bridge network can be limiting for multi-service applications.

To create a custom network, you use the docker network create command. The most common type is a bridge network, which acts like a virtual switch.

It provides better isolation and easier service discovery by name for containers connected to it.

You can connect a new container to a custom network right when you start it using the --network flag. This is the most common way to get your services talking from the start.

Containers on the same custom bridge network can communicate with each other using their container names as hostnames.

Let's create a custom network and run an Nginx web server on it. We'll publish port 8080 to access it from our host.

First, create the network, then run the container:

What if you have a container already running and want to connect it to a new custom network? You can use the docker network connect command.

This is useful when you want to dynamically add a container to a network without restarting it.

Let's say you have a simple Alpine container running. We'll connect it to our previously created my_web_network to allow it to communicate with my_nginx.

First, run a container, then connect it:

To understand what's happening inside your networks, use docker network inspect. This command shows detailed information, including connected containers and their IP addresses.

It's crucial for debugging network issues and verifying connections.

When containers are no longer needed on a network, you can disconnect them. When a network is no longer in use, it's good practice to remove it to keep your Docker environment tidy.

• docker network disconnect [network] [container]
• docker network rm [network_name]

Remember to stop and remove all connected containers before removing a network.

In this lesson, you learned how to create and manage custom Docker networks. These networks provide essential isolation and allow your containers to communicate securely by name.

• Used docker network create to make custom networks.
• Connected containers with --network or docker network connect.
• Inspected networks using docker network inspect.
• Cleaned up with docker network disconnect and docker network rm.

Mastering custom networks is vital for building robust multi-container applications.