A Docker network is a virtual network that enables communication between containers. It allows containers on the same network to reach each other using service or container names as hostnames, which is essential for applications like web apps connecting to databases. Docker provides default networks such as bridge, host, and none, but custom networks offer better control and isolation. To create a Docker network, use the command docker network create my_network, with optional flags like --subnet or --gateway for customization. Containers can be attached to a network at runtime with --network, or after starting with docker network connect. Best practices include avoiding the default bridge network, using container names instead of IPs for DNS resolution, and cleaning up unused networks with docker network prune. Multiple networks can be used simultaneously to manage access and isolation effectively.

When you're working with Docker, containers often need to talk to each other — whether it's a web app connecting to a database or multiple microservices coordinating. That’s where Docker networks come in. They’re how Docker enables communication between containers, and sometimes even with the outside world.

What Exactly Is a Docker Network?

A Docker network is a virtual network managed by Docker that allows containers to communicate with each other. Think of it like a private internal network just for your containers. By default, every container runs in its own isolated environment, but when they're on the same Docker network, they can reach each other using service names or container names as hostnames.

For example, if you have a web app container trying to connect to a database container, they can only do so if they are on the same network — otherwise, the web app won’t be able to resolve the database hostname.

Docker provides some default networks (like bridge, host, and none), but you’ll usually want to create custom ones for better control and isolation.

How to Create a Docker Network

Creating a Docker network is straightforward. You can use the docker network create command followed by a name:

docker network create my_network

This creates a new user-defined bridge network called my_network. Once created, you can attach containers to this network when you run them.

Here are a few options you might find useful:

• Use --driver to specify a different network driver if needed.
• Use --subnet and --ip-range to define custom IP ranges.
• Use --gateway to set a specific gateway.

But for most basic use cases, the default settings work just fine.

Attaching Containers to a Network

Once you’ve created a network, the next step is to connect containers to it. You can do this in two main ways:

• When starting a container, use the --network flag:

  docker run -d --name my_container --network my_network my_image

• Or connect an already running container using:

  docker network connect my_network existing_container

  After that, any other container on my_network will be able to reach my_container by its name.

  This becomes especially powerful when using Docker Compose, where services defined in the same compose file automatically share a default network unless specified otherwise.

  Common Use Cases and Tips

  One of the most common scenarios is setting up a network for a multi-container app — say, a frontend, backend, and database. All three can live on the same network, allowing them to communicate seamlessly without exposing unnecessary ports to the host machine.

  Some quick tips:

  • Avoid using the default bridge network for inter-container communication; user-defined networks provide better discovery and connectivity.
  • If containers aren’t communicating, double-check that they're on the same network.
  • Don't rely solely on IPs for communication — use container names instead, since Docker handles DNS resolution automatically on custom networks.
  • Clean up unused networks with docker network prune to keep things tidy.

  Also, remember that containers can be part of multiple networks at once. This lets you isolate sensitive services while still allowing shared access when needed.

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  That's the basics of Docker networking. It may seem minor, but getting your networks right makes managing containers much smoother.

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