User defined bridge on Docker network

A user-defined bridge network in Docker provides enhanced networking capabilities compared to the default bridge network. It allows containers to communicate using container names instead of IP addresses, offers better isolation, and provides more flexible network management options.

Advantages of User-Defined Bridge Networks

User-defined bridge networks offer several key benefits over default bridge networks:

• Name-based communication − Containers can access each other using names or aliases instead of IP addresses

• Better isolation − Only containers within the same user-defined network can communicate with each other

• Dynamic connectivity − Containers can be connected or disconnected from networks without stopping them

• Automatic port exposure − All ports are exposed between containers in the network but not to the external world

• Configurable network settings − Custom subnet ranges, gateway addresses, and DNS settings

Creating and Using User-Defined Bridge Networks

Step 1: Create a Bridge Network

Create a user-defined bridge network using the following command:

sudo docker network create --driver bridge my-alpine-net

This command returns the network ID of the newly created network.

Step 2: List Networks

Verify that the network has been created successfully:

sudo docker network ls

You will see the my-alpine-net network listed with the bridge driver and local scope.

Step 3: Inspect the Network

Examine the network configuration:

sudo docker network inspect my-alpine-net

Initially, the network will show no containers associated with it.

Step 4: Create Test Containers

Create three Alpine containers with different network configurations:

# Container connected to default bridge network
sudo docker run -dit --name my-alpine-01 alpine ash

# Container connected to user-defined network
sudo docker run -dit --name my-alpine-02 --network my-alpine-net alpine ash

# Container connected to both networks
sudo docker run -dit --name my-alpine-03 alpine ash
sudo docker network connect my-alpine-net my-alpine-03

Step 5: Inspect Network Associations

Check which containers are connected to each network:

sudo docker network inspect my-alpine-net
sudo docker network inspect bridge

Communication Examples

User-Defined Network Communication

Containers in the user-defined network can communicate using names:

# From my-alpine-02 container
sudo docker attach my-alpine-02
ping -c 3 my-alpine-03

This command succeeds because both containers are in the my-alpine-net network.

Default Bridge Network Communication

Containers in the default bridge network require IP addresses:

# From my-alpine-03 container
sudo docker attach my-alpine-03
ping -c 3 172.17.0.2

This works using the IP address of my-alpine-01, but name-based communication fails:

# This will fail
sudo docker attach my-alpine-01
ping -c 3 my-alpine-03

Network Isolation

Comparison

Conclusion

User-defined bridge networks provide superior networking capabilities compared to default bridge networks. They enable name-based communication, better isolation, and dynamic network management, making them the preferred choice for multi-container applications requiring reliable inter-container communication.