How to map a docker containers directory to the host with docker-compose?

问题

Given following docker-compose.yml setup:

version: '3.7'

services:
  reverse:
    container_name: nginx-reverse-proxy
    hostname: nginx-reverse-proxy
    image: nginx:stable
    ports:
      - 80:80
      - 433:433
    volumes:
      - type: bind
        source: ./config
        target: /etc/nginx
        consistency: consistent

Results in ./config the folder beeing mapped to the container nginx-reverse-proxy and therefore in an empty /etc/nginx directory on the container.

As stated in my question the goal is to see the content, the container (from the image) creates, and make it visible to the host at ./config.

My current search constantly results in how to map directoy from host to container (which i do not want).

Any hints/solutions are appreciated. Thanks!

My current solution is ugly: I created the container with docker and copied the files from /etc/nginx to ./config. Removing the container and using the docker-compose up works and nginx starts because the needed files are already on the host.

Edit: The folder is not present at creation. Docker compese is creating the folder as stated in the docs.

回答1:

Reading from: Dockers Volume Page

Volumes have several advantages over bind mounts:

New volumes can have their content pre-populated by a container.

So a simple docker-compose (inside a folder called nginx):

version: "3.7"
volumes:
  xmpl:

services:
  testnginx:
    image: nginx:stable
    volumes:
      - xmpl:/etc/nginx

Will yield all the files on the host system via:

$ docker-compose up
$ docker inspect nginx_xmpl
...
"Mountpoint": "/var/lib/docker/volumes/nginx_xmpl/_data"

And you can then view the files on the host:

# ls /var/lib/docker/volumes/nginx_xmpl/_data                               
  conf.d       fastcgi_params koi-utf    koi-win  
  mime.types   modules        nginx.conf scgi_params    
  uwsgi_params win-utf

And finally to use it from ./config:

# ln -s /var/lib/docker/volumes/nginx_xmpl/_data ./config
# ls config
  conf.d       fastcgi_params koi-utf    koi-win  
  mime.types   modules        nginx.conf scgi_params    
  uwsgi_params win-utf

回答2:

From what I understood, you want a way to transfer the files from your docker container to the host using docker-compose file. You should try changing the volumes as follows :

volumes:
      - /path/to/folder/on/container:/host/folder/path

As a reference you should look at an already answered question which looked similar to yours: https://stackoverflow.com/a/53930043/12485228

I hope it helps.

回答3:

Generally, it is not possible since containers are just "runnable images" and stored like a batch of zip files in the fs. On run event, they are flattened to a "folder" where Linux core does a chroot and starts processes using this root.

OPTIONALLY you can at the end of the process map some paths from the host OS to some paths in the chrooted folder, but not the way back. When Docker makes the mapping, it replaces path completely, so all the existing files in the path will "hidden" from the image fs and "replaced" by the mapped host path.

I think you want to take a look at "default files configuration" for a path in an image. There are two ways from my point of view:

Start a container with mapped path to another directory and when your container starts just copy the required folder contents using the container shell to the mapped folder. Example: let's map /export to the host's ./exported-configs and when container starts go into the running container using docker exec {.... extra params and docker ps id} bash and run something like cp -R /etc/nginx /export/nginx-configs.
export the whole image filesystem using https://docs.docker.com/engine/reference/commandline/export/ and take a look at the interesting image configuration and so it.

Both ways are working, usually, I do the first one if I need any folders from the image.

Good luck!

回答4:

Well, you shouldn't do the mapping the way you do it, cause as you said it's ugly. The most convenient and hassle-free way to do it is like so:

version: '3.7'

    services:
      reverse:
        container_name: nginx-reverse-proxy
        hostname: nginx-reverse-proxy
        image: nginx:stable
        ports:
          - 80:80
          - 433:433
        volumes:
          - ./nginx-conf/myapp/nginx.conf:/etc/nginx/nginx.conf
          - ./nginx-conf/myapp/sites-enabled:/etc/nginx/sites-enabled


    volumes:
      nginx-conf:
    networks:
      myapp-net:
        driver: bridge

The location /etc/nginx contains also other files, (mime.types and fastcgi_params for instance) which will not exist if you map the host directory ./config, unless of course, you copy them to the host instead, but that's not a pretty solution.

Above, i just mapped a local nginx.conf file, located in /nginx/myapp folder to /etx/nginx/nginx.conf and a local sites-enabled folder to /etc/nginx/sites-enabled folder in the container.

You would be better off by keeping things as simple as possible because docker is already complicated by nature.

回答5:

Not really possible. Docker volumes are mounted into the container. Does not work the other way around. Possible alternative here: https://stackoverflow.com/a/41914917/5586914

来源：https://stackoverflow.com/questions/59159241/how-to-map-a-docker-containers-directory-to-the-host-with-docker-compose

标签

Docker

docker-compose