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Version: 1.5.0

Custom configs for containers

Problem definition​

A users has a docker image from which his software can be started. The image contains pre-compiled binaries with a default configuration. However, in many cases (robotics applications), the user's software needs to be started with different configuration each time. Configuration can be facilited by several mechanisms:

  • config files,
  • ROS launch files,
  • shell scripts,
  • additional files loaded in runtime.

These custom configuration files, which are handed to the software in runtime, need to be exposed to the container runing from the user's docker image.

Our solution​

We pack the configurations (shared data) in a dedicated transport image which is easily delivered to the robot. Then, during runtime, this image spawns a container in which the data is coppied to a shared docker volume. Then, the user's containers are started, all mounting the same shared docker volume and accessing the configuration data.

Packing shared data to a transport image​

The following minimalistic dockerfile coppies the shared_data subfolder in the transport docker image:

FROM alpine

COPY shared_data/ /etc/docker/shared_data/

CMD ["sh"]

Build the image using the following command. Select the appropriate tag and platform.

docker build build . --file Dockerfile --tag <shared_data_image_tag> --platform=linux/<my_platform>

Unloading the shared data from the transport image​

The following compose session shows the process of unloading the shared data. The user_program can then access the files in the shared docker volume.

volumes:

  shared_data:

services:

  # will copy session-specific data shared between containers from the shared_data container to a shared volume
  copy_shared_data:
    image: <shared_data_image_tag>
    volumes:
      - shared_data:/tmp/docker/shared_data:consistent
    tty: true
    command: sh -c "rm -rvf /tmp/docker/shared_data/*; mkdir -pv /tmp/docker/shared_data; cp -rv /etc/docker/shared_data/* /tmp/docker/shared_data/"

  user_program:
    image: <users_base_image>
    depends_on:
      - copy_shared_data
    volumes:
      - shared_data:/etc/docker/shared_data:consistent
    command: my_process /etc/docker/shared_data/config_file.txt