3.3: The Bridge network: Creating an insulator so that our containers can communicate with each other (Docker network)

Creating a gateway so our containers can communicate with each other (docker network)

When you have multiple containers, the question quickly arises: How will my containers communicate with each other?

Docker provides a simple solution: networks, and in particular the bridge network.

The concept: an isolated network

A bridge network is like a small internal private network for your containers.

• Containers connected to the same network can communicate directly.
• By default,Docker creates a networkbridge called bridge, but it’s often better to create your own dedicated network for your projects.

Example of creating a network:

docker network create mon_reseau

• mon_reseau will be an isolated network
• Only containers connected to this network will be able to communicate with each other.

Launching containers on a network

docker run -d --name web --network mon_reseau nginx
docker run -d --name db --network mon_reseau mariadb

• The containerweb can now contactdb via its service name: db:3306
• No need to configure external ports for this internal communication.

Internal communication

• Containers on the same network see each other’s names as internal DNS entries.
• Example:

docker exec -it web ping db

• Here,web can pingdb directly, without going through fixed IP addresses.
• Docker handles internal name resolution automatically.

Multiple networks supported

You can connect a container to multiple networks if necessary:

docker network create reseau_front
docker network create reseau_backdocker run -d --name web --network reseau_front nginx
docker network connect reseau_back web

• web can now communicate with containers on front_network and back_network.
• Very useful for separating layers: front-end / back-end / database.

Other network types Docker

Docker offers several network types depending on your needs:

Network type	Main purpose
bridge	Isolated internal network, default for most projects
Host	Container shares the host’s network, no isolation
macvlan	Each container has its own IP address on the physical network
overlay	Multi-host networks, used withDockerSwarm

Check networks and containers

To list networks:

docker network ls

To inspect a network and view the connected containers:

docker network inspect mon_reseau

• You can then see the containers, their internal IPs, and the associated subnet.

Simplified visual diagram

      [ bridge network : mon_reseau ]
      ------------------------------
      |        |                     |
   web:80   db:3306                autre:5000
      |        |                     |
      ------------------------------
            Communication interne via noms

• All containers connected to the same network can communicate directly with each other
• External ports are not required for this internal communication.
• The network is isolated from the outside world, unless a port is mapped.

Useful commands for managing networks Docker

Here are the most useful commands for creating, inspecting, and cleaning up your networks:

List all networks

docker network ls

• DockerDisplays all existing networks on your machine.
• Example output:

NETWORK ID     NAME         DRIVER    SCOPE
a1b2c3d4e5f6   bridge       bridge    local
b2c3d4e5f6g7   mon_reseau   bridge    local

Inspect a network

docker network inspect mon_reseau

• Shows connected containers, their internal IPs, the subnet, etc.
• Very useful for debugging internal communication.

Create a custom network

docker network create mon_reseau

• Creates an isolated bridge network named mon_reseau.
• You can connect existing containers to this network:

docker network connect mon_reseau mon_conteneur

Disconnect a container from a network

docker network disconnect mon_reseau mon_conteneur

• Disconnects the container without stopping it.
• Useful if you want to reorganize your networks dynamically.

Delete a network

docker network rm mon_reseau

• Deletes the network (connected containers must be disconnected first).

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🔹 Note

This section on networksDockerhas been briefly covered to give you the essential basics.

• Some topics can be explored in greater depth through detailed tutorials on our website.
• Other concepts, such as advanced networks (macvlan, overlay, multi-host), will be covered in an intermediate courseDocker.

The goal here is to understand the general operation of bridge networks and internal communication, so you can safely deploy your first stacks.