how to pass argument (file path) to python app in Docker

Question

I have a python application that is expecting first argument as file path. basically a configuration file.

This file it should get form volume/ mount in Docker

How to pass this:

. Snippets Python:

with open(sys.argv[1], 'r') as ymlfile:
    cfg = yaml.load(ymlfile)

Docker file

COPY install.py /wiki/install.py
CMD [ "python", "/wiki/install.py", "/config/config.yml"]

Run image command

sudo docker run -v /config:/home/example/config/ app-wiki

I am expecting config.yml file available at /home/example/config/ will be copied in /config dir and inside Docker file it will be available

but its not working this way.

Where I am going wrong?

Answer 1

The way docker CMD works is you need to make sure that the file is copied into the correct location with correct permissions.

Example:

RUN mkdir -p /config
RUN mkdir -p /wiki
ADD cp <your-location> /config/config.yml
ADD install.py /wiki/install.py
CMD [ "python", "/wiki/install.py", "/config/config.yml"]

Also, docker will keep the same permissions that you have in your local directory. So, make sure you have correct permission set on both files.

Answer 2

The issue is that you have got the direction wrong. The format is <hostpath>:<containerpath>

Below

sudo docker run -v /config:/home/example/config/ app-wiki

should be

sudo docker run -v /home/example/config/:/config app-wiki

Doing the config present in /home/example/config/ will be available in container at /config folder

Edit-1

Added a bit of more explanation to clear you doubts.

COPY install.py /wiki/install.py
CMD [ "python", "/wiki/install.py", "/config/config.yml"]

When you run the above image it will expect a config to be available at /config/config.yml .

Now if you have a folder on your host /home/tarun/wikiconfig which has a config.yml file then you run the container using

sudo docker run -v /home/tarun/wikiconfig:/config app-wiki

If the name of the config.yml file is different in your wikiconfig folder, then you will mount the file to config.yml

sudo docker run -v /home/tarun/wikiconfig/myconfig.yml:/config/config.yml app-wiki

Both would override the config you added when you build the Dockerfile, because when you a mount a folder or file from host, anything with the same path inside container is no more accessible to the image