Mounted host file becomes a directory inside a docker container

Question

I mount a host file into a docker container, and the mounted file becomes a directory inside the container. That's how I run it:

$ docker run --name <containername> -it -d -v /home/core/account_config.py:/code/account_config.py <imagename>

Inside the container:

 # ls -la -rw-r--r--. 4 root root 0 Nov 6 10:25 __init__.py drwxr-xr-x. 2 root root 4096 Nov 6 10:59 account_config.py ....

The file (in the host file system) is still a perfectly ok python file.

The source code is added into /code during build. The corresponding line in my Dockerfile is:

ADD ./code /code

I want to be able to change the content of config file without rebuilding the image, so I want mount it later. What went wrong and how can I fix this?

@AdrianMouat your comment gave me an idea to report it as a bug. While preparing a bug report, I tried to replicate it in some minimal example, and figured out what went wrong. Thank you :) — t_tia
– t_tia, Commented Nov 6, 2015 at 14:02
Interesting, I didn't actually know it would do that if the directory doesn't exist on the host. Not sure I was much help, but I'm glad you got it sorted. — Adrian Mouat
– Adrian Mouat, Commented Nov 6, 2015 at 14:29

t_tia · Accepted Answer · 2015-11-06 13:59:58Z

As it happens with (almost) every weird issue, turned out that this one has a very simple solution.

The path to host file contained a typo, so the docker automatically created a directory in this path, and mounted it to the container.

carter · Accepted Answer · 2015-11-06 21:19:01Z

If you want to be able to modify a file on the host machine and have changes reflect within a container, you should mount the volume via -v HOST_PATH:CONTAINER_PATH when you run the container.

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