Docker None Network

Introduction

When working with Docker containers, networking is a critical aspect that determines how containers communicate with each other and the outside world. Docker provides several built-in network drivers to address different networking requirements. One of these is the none network driver, which is sometimes overlooked but serves important use cases in containerized environments.

The none network driver creates containers with no external network interfaces. This might seem counterintuitive at first—why would you want a container with no network connectivity? However, there are specific scenarios where this level of isolation is exactly what you need.

In this guide, we'll explore the none network driver in depth, its characteristics, use cases, and limitations.

What is the None Network?

The none network is a special network type in Docker that provides maximum network isolation. When you attach a container to the none network:

• The container receives only a loopback interface (lo)
• No external network interface is created
• The container cannot communicate with other containers or the host
• No incoming or outgoing network connections are possible beyond the container itself

Here's a visual representation of the none network:

Creating a Container with the None Network

To create a container using the none network, you can use the --network=none flag with the docker run command:

bash

docker run --network=none -it ubuntu bash

Let's verify the network interfaces inside the container:

bash

# Inside the container
ip addr show

Output:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever

Notice that only the loopback interface (lo) is available. There are no eth0 or other network interfaces that would typically be present in a networked container.

Inspecting the None Network

Let's examine the none network using the Docker network inspection command:

bash

docker network inspect none

Output:

json

[
    {
        "Name": "none",
        "Id": "3d4821e424d1ac089b8f9a664331ff76adb172810f8a8a16e9ede0e2165fb963",
        "Created": "2023-03-15T14:27:46.285789277Z",
        "Scope": "local",
        "Driver": "null",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": []
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {},
        "Options": {},
        "Labels": {}
    }
]

Key things to notice:

• The driver is actually called null, though we refer to it as the none network
• There is no IP configuration ("Config": [] in the IPAM section)
• The network is not attachable, not internal, and not used for ingress

Use Cases for the None Network

1. Security-Critical Applications

For applications handling extremely sensitive data, the none network provides the highest level of network isolation. Since the container cannot communicate with anything outside itself, the attack surface from a network perspective is minimized.

bash

docker run --network=none -v /secure/data:/data secure-processor

2. CPU-Intensive Batch Processing

For containers that perform computational tasks without needing network access, the none network eliminates unnecessary overhead:

bash

docker run --network=none number-cruncher --input /data/input.dat --output /data/result.dat

3. Local Development and Testing

When developing applications that don't require network access or when you want to test application behavior in the absence of network connectivity:

bash

docker run --network=none -v $(pwd):/app my-app-test

4. Custom Network Namespaces

Advanced users might want to set up their own network namespace manually:

bash

# Run with none network
docker run --network=none -d --name custom-net-container alpine sleep infinity

# Get container PID
PID=$(docker inspect -f '{{.State.Pid}}' custom-net-container)

# Set up custom networking (example)
sudo ip link add eth0 type veth peer name veth0
sudo ip link set veth0 netns $PID
sudo nsenter -t $PID -n ip addr add 192.168.1.100/24 dev veth0
sudo nsenter -t $PID -n ip link set veth0 up

Testing Network Isolation

Let's verify that a container with the none network truly has no external connectivity:

bash

# Create a container with the none network
docker run --network=none --name isolation-test -d alpine sleep infinity

# Try to ping Google's DNS from inside the container
docker exec isolation-test ping -c 1 8.8.8.8

Output:

ping: sendto: Network unreachable

Trying to access the internet or any external resource will fail with a "Network unreachable" error, confirming the isolation.

Limitations and Considerations

When using the none network, be aware of these limitations:

1. Data Exchange: Since the container cannot connect to networks, you must use volume mounts to get data in and out of the container.

   bash

   docker run --network=none -v /host/path:/container/path my-isolated-app

2. No Docker DNS: DNS resolution services provided by Docker are not available.

3. Resource Access: The container cannot access external resources like databases, APIs, or package repositories.

4. Container Linking: Traditional Docker container linking won't work with the none network.

5. Health Checks: If your container relies on network-based health checks, you'll need alternative mechanisms.

6. Debugging Challenges: Debugging can be more difficult without network access to the container.

None Network vs. Host Network

It's worth comparing the none network with another special network type in Docker - the host network:

Feature	None Network	Host Network
Network isolation	Complete isolation	No isolation
Network interfaces	Only loopback (lo)	All host interfaces
Network performance	N/A (no network)	Native (no overhead)
Security	Highest network security	Lowest network security
Use cases	Batch processing, security-critical apps	High-performance networking
Command	--network=none	--network=host

Practical Example: Secure File Processing

Here's a practical example of using the none network for a container that needs to process sensitive files without network access:

bash

# Create directories for input and output
mkdir -p /secure/input /secure/output
echo "sensitive data" > /secure/input/data.txt

# Run a file processor with no network
docker run --network=none \
    -v /secure/input:/input:ro \
    -v /secure/output:/output \
    secure-file-processor \
    --input=/input/data.txt \
    --output=/output/processed.txt

In this example:

• The container has read-only access to the input directory
• It can write to the output directory
• It has no network access, preventing data exfiltration
• The :ro flag makes the input volume read-only for additional security

Summary

The Docker none network provides the highest level of network isolation for containers. By removing all external network interfaces and limiting the container to just a loopback interface, it creates a secure environment for running applications that don't need network connectivity.

Key takeaways:

• The none network provides maximum network isolation
• Containers on this network have only a loopback interface
• It's ideal for security-critical applications and CPU-intensive tasks
• Data exchange must happen through volume mounts
• The isolation brings limitations that must be considered in your application design

While not suitable for all use cases, the none network is a valuable tool in Docker's networking toolkit, especially for scenarios where security and isolation are paramount.

Additional Resources

To deepen your understanding of Docker networking:

• Explore other Docker network drivers: bridge, host, overlay, and macvlan
• Learn about Docker volume mounts for data exchange
• Study container security best practices
• Practice creating multi-container applications with different network configurations

Exercises

1. Create a container with the none network and verify it has no external network interfaces.
2. Write a simple application that processes a file locally and deploy it in a container with the none network.
3. Compare the resource usage between identical containers using the none network and the default bridge network.
4. Design a secure data processing pipeline using containers with the none network for the processing stage.
5. Implement a custom solution to get logs out of a container running with the none network.