How to mount a single file in a volume
The way that worked for me is to use a bind
mount
version: "3.7"
services:
app:
image: app:latest
volumes:
- type: bind
source: ./sourceFile.yaml
target: /location/targetFile.yaml
Thanks mike breed for the answer over at: Mount single file from volume using docker-compose
You need to use the "long syntax" to express a bind
mount using the volumes
key: https://docs.docker.com/compose/compose-file/compose-file-v3/#long-syntax-3
TL;DR/Notice:
If you experience a directory being created in place of the file you are trying to mount, you have probably failed to supply a valid and absolute path. This is a common mistake with a silent and confusing failure mode.
File volumes are done this way in docker (absolute path example (can use env variables), and you need to mention the file name) :
volumes:
- /src/docker/myapp/upload:/var/www/html/upload
- /src/docker/myapp/upload/config.php:/var/www/html/config.php
You can also do:
volumes:
- ${PWD}/upload:/var/www/html/upload
- ${PWD}/upload/config.php:/var/www/html/config.php
If you fire the docker-compose from /src/docker/myapp
folder
Use mount (--mount
) instead volume (-v
)
More info: https://docs.docker.com/storage/bind-mounts/
Example:
Ensure /tmp/a.txt exists on docker host
docker run -it --mount type=bind,source=/tmp/a.txt,target=/root/a.txt alpine sh
I had been suffering from a similar issue. I was trying to import my config file to my container so that I can fix it every time I need without re-building the image.
I mean I thought the below command would map $(pwd)/config.py
from Docker host to /root/app/config.py
into the container as a file.
docker run -v $(pwd)/config.py:/root/app/config.py my_docker_image
However, it always created a directory named config.py
, not a file.
while looking for clue, I found the reason(from here)
If you use -v or --volume to bind-mount a file or directory that does not yet exist on the Docker host, -v will create the endpoint for you. It is always created as a directory.
Therefore, it is always created as a directory because my docker host does not have $(pwd)/config.py
.
Even if I create config.py in docker host.
$(pwd)/config.py
just overwirte /root/app/config.py
not exporting /root/app/config.py
.