Docker-compose - Providing XML based configuration to docker container running spring boot standalone application

Question

I want to know how to configure a docker setup (docker-compose) in order to supply a configuration file which is consumed by my Spring boot application.

The configuration file is called services.xml which resides in the applications's /lib/conf directory. The file is deployed with the default configuration, however I want the file in host so that whenever I need to change the configuration, I should edit in host and the container would read the updated file.

The docker-compose.yml

version: '3.1'

services:

  my-app:
    image: my-app
    container_name: my-app
    # restart: always
    ports:
      - 8443:8443
    volumes:
      - ./my-app/conf:/opt/lib/my-app/lib/conf:rw

Expected results after running: docker-compose up

I expect this should create the directory, copy the default services.xml (along with all other files in /opt/lib/my-app/lib/conf) in container into this directory to make it available for me to edit.

Actual results After running docker-compose, it creates an empty directory inside the my-app directory. The my-app fails to read the services.xml file and app doesn't start (as it depends on this file).

Answer 1

I expect this should create the directory, copy the default services.xml (along with all other files in /opt/lib/my-app/lib/conf) in container into this directory to make it available for me to edit.

From you said above, if your aim is to let the contents in container be pop to host & let you have chance to modify them, then I suggest you to use named volumes . But, the folder in host will be managed by docker itself, so you need to find where they are located.

A minimal example for your reference:

docker-compose.yaml(In my example it located in the folder 77 ):

version: '3'
services:
  frontend:
    image: alpine
    command: "tail -f /dev/null"
    volumes:
      - my_data:/etc

volumes:
  my_data:

Start the service:

shubuntu1@shubuntu1:~/77$ docker-compose up -d
Creating network "77_default" with the default driver
Creating volume "77_my_data" with default driver
Creating 77_frontend_1 ... done

Check the location of named volume in host:

shubuntu1@shubuntu1:~/77$ docker ps
CONTAINER ID    IMAGE     COMMAND               CREATED             STATUS          PORTS     NAMES
6635aba545c9    alpine    "tail -f /dev/null"   14 minutes ago      Up 14 minutes             77_frontend_1
shubuntu1@shubuntu1:~/77$ docker inspect 77_frontend_1 | grep Source
            "Source": "/var/lib/docker/volumes/77_my_data/_data",

Check the content of original /etc/profile in container:

shubuntu1@shubuntu1:~/77$ docker exec 77_frontend_1 cat /etc/profile
export CHARSET=UTF-8
export LANG=C.UTF-8
export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
export PAGER=less
export PS1='\h:\w\$ '
umask 022

for script in /etc/profile.d/*.sh ; do
    if [ -r $script ] ; then
            . $script
    fi
done

Modify the script from host:

shubuntu1@shubuntu1:~/77$ sudo -s -H
root@shubuntu1:/home/shubuntu1/77# cd /var/lib/docker/volumes/77_my_data/_data
root@shubuntu1:/var/lib/docker/volumes/77_my_data/_data# echo 'echo "hello"' >> profile

Check again the /etc/profile in container after we made changes on host:

shubuntu1@shubuntu1:~/77$ docker exec 77_frontend_1 cat /etc/profile
export CHARSET=UTF-8
export LANG=C.UTF-8
export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
export PAGER=less
export PS1='\h:\w\$ '
umask 022

for script in /etc/profile.d/*.sh ; do
    if [ -r $script ] ; then
            . $script
    fi
done
echo "hello"

We can see echo "hello" which we add on host already be seen in container.