Docker Can't find kubernetes Config File

Question

I'm trying to containerize a python application, where I used the Kubernetes package. My Dockerfile is:

FROM python:3.10.6

ADD App_pod.py .
ADD config.yml ~/.kube/config

RUN pip3 install requests beautifulsoup4
RUN pip3 install kubernetes
RUN apt-get install -y ca-certificates curl

CMD ["python3","./App_pod.py"]

when I enter docker run -i -t run, it shows me the following error:

> Traceback (most recent call last):
> File "//./App_pod.py", line 9, in <module>
> config.load_kube_config()
> File "/usr/local/lib/python3.10/site-packages/kubernetes/config/kube_config.py", line 813, in load_kube_config
> loader = _get_kube_config_loader(
> File "/usr/local/lib/python3.10/site-packages/kubernetes/config/kube_config.py", line 770, in _get_kube_config_loader
> raise ConfigException(
> kubernetes.config.config_exception.ConfigException: Invalid kube-config file. No configuration found.

I tried to change the appearing error from raise exeption but it still shows me the same error, so I guess maybe it doesn't detect the changes I do.

I used ADD command to copy the config file to the specific path, but it still shows the same error. I also tried to mount the volume but it can't be mounted since there is no container yet, because it needs first the conf file to be created. Does anyone face this problem and know how to fix it?

Answer 1

A couple of issues:

• ~ has a special meaning on Linux; it is a shortcut to the user's home directory. I think ~ is not available for the destination path of a Dockerfile ADD (or COPY) command. You should use a specific path instead
• It's not advisable to include a file that includes credentials (such as a kubeconfig file) in a container. You should instead mount data such as this.
• You're renaming the file config.yml is the source but config is the destination which may be problematic.

You don't include the full Dockerfile so it's unclear what your FROM image is and you don't include the source of your App_pod.py file so it's unclear where it looks for the kubeconfig file, but...

1. Generalize your code's use of the kubeconfig file by providing it as an argument or using an environment variable. This way, the location is dynamic and the code can work when run outside of a container or within
2. Mount the file into the container when you run the container

Let's assume you change your code to accept a command-line argument for config.yml in the working directory, e.g.:

python3 App_pod.py ~/.kube/config

Then, when you run the container, you will need to mount the config.yml into the container and reference it. In the following, I'm using different source and destination folders to demonstrate the point:

docker run \
--interactive --tty --rm \
--volume=~/.kube/config:/somewhere/.kube/config \
your-container /somewhere/.kube/config

You can use ~ in the --volume flag because ~ is meaningful on your (Linux) host. The file is mapped to /somewhere/.kube/config in the container and so your Python file needs to point to the container location (!) when you invoke it.

Also, so that you may use command-line parameters, I encourage you to use ENTRYPOINT instead of CMD to run your Python program:

...
ENTRYPOINT ["python3","./App_pod.py"]