Add veth to your Docker container or connect your containers with veths in one step

Let me introduce you an ultimate BASH script for easily extend a running Docker container with a new veth interface or creates more veths for more containers and connect them!

There is also a script that simply creates a network namespace for your running container on your host to use ip netns commands.

Get (into) it

$ git clone https://github.com/cslev/add_veth_to_docker

$ cd add_veth_to_docker

Usage

$ sudo ./add_veth2container <container_name> <veth_name_at_host> <veth_name_in_container>

Note

<container_name> is not the image name, as you can have multiple containers running the same image. If you do not provide any name for your running container during the init phase, Docker automatically assigns one to it.

To specify an own name to your container use --name <my_container> argument when starting the container.

If your container is already running, you can distille the output of docker ps command to figure out what is the name of the corresponding container.

What it does

• checks whether the veth pair and the container you want to connect the veth pair to is up and running
• binds a pointer to the container's namespace in the root namespace to enable the usage of ip netns
• creates a veth pair with the required names and binds the latter end of it to the container
• brings up each end of the veth pair that becomes ready to use immediately
• cleans up the mess in case of an error during the process

What it denitiely does not do

• pre-installs any requirements (e.g., net-tools, docker)
• boots up your container
• do any further things with freshly made interfaces (e.g., connect to internet/hypervisor switch)

Example output

$ sudo ./add_veth2container.sh admiring_mahavira veth_root veth_container
Checking whether container admiring_mahavira is running...[OK]
admiring_mahavira is found and up and running

Getting PID of the running container admiring_mahavira: [OK] (24617)

Creating /var/run/netns/ directory...[OK]

Create a symlink admiring_mahavira in /var/run/netns/ pointing to /proc/24617/ns/net...[OK]

Create veth pair veth_root -- veth_container...[OK]

Bringing up veth_container...
[OK]

Bringing up veth_root...
[OK]

Add veth_container to container admiring_mahavira...[OK]

Bring up manually the interface in the container as well...[OK]

Possible errors and their outputs

Interface you wanted to create already exists:

$ sudo ./add_veth2container.sh admiring_mahavira veth_root veth_container
There is an interface called veth_root...

Please use another name or remove manually by:
	$ sudo ip link del veth_root

Container does not exist or is not up and running

$ sudo ./add_veth2container.sh macskas_macska veth_roota veth_container
Checking whether container macskas_macska is running...[FAILURE]
macskas_macska is not running
Use sudo docker ps -a to find out more on your own

[FAILED]


Cleaning up...
Removing symlink (if created)...[OK]

Removing veth pair (if created)...[OK]

Connecting multiple containers with vets (connect_containers_veth.sh)

A slightly modified version of the script has been added to the repository, which not just creates a veth pair and adds one of the ends to a container, but the other end can be added to another container. Use if some networking is intended to be used between containers without involving the 'hypervisor' layer. Note that IP address management still needs to be done from the host machine via ip netns exec ... commands

Usage

$ sudo ./connect_containers_veth.sh <container_name1> <container_name2> <veth_name_in_container1> <veth_name_in_container2>

Basic ip netns creation for a running container (create_namespace4container.sh)

Another snippet from the main script has been extracted to do smaller things :) This script only creates an ip netns namespace for the container but nothing more. This way one can do the further things on his/her own, e.g., adding a physical interface to the container.

$ sudo ./create_namespace4container.sh <container_name>